Total Hip Arthroplasty: Wear Behaviour of Different Articulations

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Total Hip Arthroplasty

Karl Knahr Editor

Total Hip Arthroplasty Wear Behaviour of Diﬀerent Articulations

Editor Prof. Dr. Karl Knahr Orthopaedic Hospital Vienna-Speising Vienna Austria

ISBN 978-3-642-27360-5 e-ISBN 978-3-642-27361-2 DOI 10.1007/978-3-642-27361-2 Springer Heidelberg New York Dordrecht London Library of Congress Control Number: 2012934742 © EFORT 2012 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, speciﬁcally the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microﬁlms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. Exempted from this legal reservation are brief excerpts in connection with reviews or scholarly analysis or material supplied speciﬁcally for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Duplication of this publication or parts thereof is permitted only under the provisions of the Copyright Law of the Publisher’s location, in its current version, and permission for use must always be obtained from Springer. Permissions for use may be obtained through RightsLink at the Copyright Clearance Center. Violations are liable to prosecution under the respective Copyright Law. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply , even in the absence of a speciﬁc statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein. Printed on acid-free paper Springer is part of Springer-Verlag Berlin Heidelberg (www.springer.com)

Preface

There are four important criteria essential for a successful implant to achieve long-term stability and function: material, design, ﬁxation of the prosthesis and wear of the articulation. Stability is achieved by ﬁxation with bone cement or cementless press-ﬁt using different designs of stems and cups. There are hundreds of implants on the market, all of them offering excellent results when used. In contrast to the numerous implant designs, there are only three materials available to support the demands of long-term function: polyethylene, metal and ceramics. Wear of these articulating materials is one of the most important factors for successful long-term results in total hip arthroplasty. In the early days of total hip arthroplasty, a metal head articulating with a conventional polyethylene cup was the gold standard. Unfortunately in many cases wear debris after longterm function resulted in osteolysis around the implant with subsequent loosening. Consequently, new materials and new options of combinations between cup and stem were introduced. Hard-on-hard bearings (metal-on-metal, ceramic-on-ceramic) became more and more popular, but their popularity was compromised by allergic reaction of metal, pseudotumours, fracture or squeaking of the articulating material. Consequently implant companies focused on development activities to overcome the shortcomings of their products. Conventional polyethylene was improved by high cross-linking techniques and furthermore by adding vitamin K. Pure aluminium oxide ceramic was improved by introducing ceramic composite implants. The Tribology Day at the 12th EFORT Congress in Copenhagen focused on all these new products and their effectiveness in clinical use. Polyethylene topics cover the analysis of influence of vitamin E-blended cross-linked polyethylene in in vitro wear testing as well as in long-term clinical use. Metal-on-metal articulations are recently faced with loss of reputation due to allergic reactions and pseudotumours, especially in large-diameter head implants. Retrieval analyses and clinical survival papers address these issues. Fracture and squeaking are the main concerns with ceramic-on-ceramic articulations. Their frequency and clinical relevance are discussed and long-term results presented. The authors of this book contributions hope that their chapters will meet your expectations and give a better insight to a still on-going improvement of wear reduction in total hip arthroplasty. K. Knahr

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Contents

Part I

Introduction

1 Tribology of Hip Prostheses, Wear Performance and Reliability, Effect of Materials and Head Size ..................................................................... John Fisher 2 How to Treat Failures Related to Articulation ................................................. Luigi Zagra, Luca Bianchi, and Roberto Giacometti Ceroni Part II

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Polyethylene Articulations

3 Oxidation Prevention with Vitamin E in a HXLPE Isoelastic Monoblock Pressﬁt Cup: Preliminary Results ................................................. Martin Beck, Daniel Delfosse, Reto Lerf, Roland Becker, Gary French, Lutz Hollmann, Karl Knahr, Helmy Naeder, Eric Meijer, Philipp Rehbein, Joseph Baines, Vincent Steenmeijer, and Arthur de Gast 4 In Vitro Wear Testing of Conventional Versus Sequentially Cross-Linked Polyethylene Liners in Combination with Different Sizes of Ceramic Femoral Heads ....................................................... Carmen Zietz, Andreas Fritsche, Lars Middelborg, Wolfram Mittelmeier, and Rainer Bader 5 Characterisation of Vitamin E–Blended UHMWPE for Higher In Vivo Performance in Orthopaedic Arthroplasty ......................................... Luigi Costa, Marco Regis, Pierangiola Bracco, Luca Giorgini, and Simonetta Fusi 6 Long-Term Reduction of Wear and Osteolysis with Cross-Linked PE? 13-Year Follow-up of a Prospectively Randomized Comparison with Conventional PE .................................................................................................. Bernd Grimm, Alphons Tonino, and Ide Christiaan Heyligers

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Contents

Part III 7

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Metal-on-Metal Bearings in Hip Surgery: The London Implant Retrieval Centre Experience ............................................................................ John Skinner, Alister Hart, and Ashley Matthies Total Hip Arthroplasty with a Large-Diameter Metal-on-Metal Cup (Durom) and a Standard Stem: Short-Term Results ............................ Panayiotis Christoﬁlopoulos, Anne Lübbeke, Charles Berton, Alexandre Lädermann, Martin Berli, Constantinos Roussos, Alexis Bonvin, Robin Peter, and Pierre Hoffmeyer

Immunological Adverse Reaction Associated with Low Carbide Content Metal-on-Metal Bearings in a Contemporary Cementless Total Hip Arthroplasty ..................................................................................... Panagiotis Korovessis, Thomas Repantis, Panagiotis Aroukatos, and Maria Repanti

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Fracture and Squeaking in Ceramic-on-Ceramic Bearings: Is It Really a Concern? ..................................................................................... Alexandra Pokorny and Karl Knahr Long-Term Stability of Ceramic Composite in Total Hip Arthroplasty ...... Bernard Masson and Meinhard Kuntz

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Ceramic-on-Ceramic Bearings in Hip Arthroplasty: A Clinical Review .............................................................................................. James M. Buchanan

Part V

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Ceramic Articulations

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Polyethylene Wear in Metal-Backed Cups: A Retrospective Analysis of 200 Uncemented Prostheses ................................ 99 WWalter van der Weegen, Shennah Austen, Thea Sijbesma, and Henk J. Hoekstra

Part IV 11

Metal Articulations

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Miscellaneous

Study of a Titanium Dual-Mobility Socket with a Mean Follow-up of 18 Years.......................................................................................................... Remy Philippot, B. Boyer, and F. Farizon

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ECiMa™ for Low Wear, Optimal Mechanical Properties and Oxidation Resistance of Hip Bearings............................................................................... Alison Traynor, David Simpson, and Simon Collins

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Index ...........................................................................................................................

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Part I Introduction

Tribology of Hip Prostheses, Wear Performance and Reliability, Effect of Materials and Head Size

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John Fisher

1.1 Introduction Wear and adverse reactions to wear particles remain a concern, particularly with young and active patients with long life expectancies [12, 13]. There is considerable interest in the clinical use of improved bearing materials such as cross-linked polyethylene, metal on metal, ceramic on ceramic and ceramic on metal [6]. In addition to reducing wear, there is also clinical interest in using larger head sizes to improve stability and range of motion [6]. However, in polyethylene bearings, a larger head size can lead to increased wear [8, 16]. Most previous research work has studied the wear performance of bearings under a standard set of walking conditions with components correctly positioned. Indeed, with improvements in bearing technology, the wear under standard walking conditions has reduced to low levels, and this has encouraged the use of diameter larger heads. However, in addition, it has become increasingly important to consider the wear under a much wider range of conditions and variations which may be introduced by different activities, by individual patients or the surgery (such as component position). Under a broader and more realistic set of conditions, the wear in some bearings may increase dramatically, and this may increase failure and reduce reliability [24]. In this short review, the wear performance of different bearing materials and different head sizes is considered under standard walking conditions. In addition, the tribological performance under conditions which may cause extremely high wear rates and reduce reliability and increase failure are also considered.

J. Fisher, CBE, FREng, FIMECHE, FIPEM, CEng, CSci Institute of Medical and Biological Engineering, University of Leeds, Leeds, LS2 9JT, UK e-mail: [email protected] K. Knahr (ed.), Total Hip Arthroplasty, DOI 10.1007/978-3-642-27361-2_1, © 2012 EFORT

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1.2 Polyethylene Bearings Under standard walking conditions, the wear rate of conventional size 28 mm metal on polyethylene bearings was between 30 and 40 mm3/million cycles, and these bearings can reach the cumulative threshold for osteolysis of 500 mm3 in 10–15 years [2, 4]. The wear was reduced to 25 mm3/million cycles with ceramic on polyethylene bearings [22]. Wear rate was doubled with size 36 mm heads compared to size 28 mm heads [16]. With metal heads on cross-linked polyethylene, the wear rate was substantially reduced to between 5 and 10 mm3/million cycles with size 28 mm and size 36 mm heads, respectively [8]. Thirty-six-mm ceramic femoral heads on cross-linked polyethylene reduced the wear rate to 5 mm3/million cycles [9]. In the only published study of the effect of adverse conditions of loading of the femoral head on the rim of the polyethylene cup, the wear rate did not increase [22]. Clinical studies of cross-linked polyethylene bearings have been reported for follow-ups of between 5 and 9 years and have not yet shown signiﬁcant wear debrisinduced osteolysis. Additionally, there have been only a few reported failures of crosslinked polyethylene due to adverse conditions.

1.3 Metal-on-Metal Bearings Under standard walking conditions, metal-on-metal bearings have shown low wear rates, typically less than 1 mm3/million cycles [14, 21]. Increasing the head size from 28 to 36 mm has reduced the wear rates, but a further increase in head size above 36 mm only reduced the initial bedding in wear and did not reduce the long-term steady-state wear [14]. Metal wear particles cause toxicity and produce tissue necrosis [3, 10]. Under adverse conditions of the loading of the femoral head on the rim of the cup, either due to rotational malposition of the cup or translational malposition of the head or cup, the wear rate of metal-on-metal bearings increased dramatically by between 10- and 100-fold, and this may lead to high clinical ion levels, adverse tissue reactions and failure [15, 21, 24]. The substantial increase in wear rates of metal bearings found under adverse conditions is a potential cause of early clinical failure and reduced reliability [7].

1.4 Ceramic-on-Metal Bearings The differential hardness ceramic-on-metal bearing was developed to reduce wear compared to metal-on-metal bearings. Under standard walking conditions, the wear of ceramicon-metal bearings was at least tenfold lower than metal-on metal-bearings [5]. Size 36 mm bearings had lower wear than size 28 mm bearings [23]. The wear particles produced were predominantly nanometre metallic particles [3]. Clinical studies have shown a reduction in metal ion levels in ceramic-on-metal bearings compared to metal-on-metal bearings

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[23]. Under adverse conditions of loading of the head on the rim of the cup, the wear of ceramic on metal was less than 1 mm3/million cycles substantially less than for metal-onmetal bearings under adverse conditions, indicating that ceramic on metal is a more robust and reliable bearing combination than metal on metal [23].

1.5 Ceramic-on-Ceramic Bearings Biolox Forte alumina ceramic-on-ceramic bearings and Biolox Delta alumina matrix composite bearings showed extremely low wear rates under standard walking conditions [1, 18–20]. Under standard walking conditions, there was little effect of head size on wear rates. Ceramic debris has been shown to be less toxic than metal debris [10] and less inﬂammatory than polyethylene debris [11]. Under adverse conditions of translational malposition and the head loading on the rim of the cup, the wear rates increased [17]. Under head rim loading conditions, the wear rate for alumina ceramic on ceramic increased to greater than 1 mm3/million cycles [18], but for alumina matrix composite, the increase was less with a wear rate of less than 1 mm3/million cycles [1, 20].

1.6 Discussion During the 1990s, conventional polyethylene bearings produced extensive wear debrisinduced failure and osteolysis in hip joint replacements [12, 13]. Under normal walking conditions, cross-linked polyethylene, metal-on-metal, ceramic-on-metal and ceramic-onceramic bearings all have substantially reduced wear rates compared to conventional polyethylene, and under standard walking conditions, these bearings are likely to deliver good clinical outcome over the ﬁrst 15–20 years’ clinical use. In this respect, these bearing material developments have substantially addressed the challenge of short- and mediumterm wear debris-induced osteolysis seen in the 1990s with conventional polyethylene. Long-term clinical studies over 20 years follow-up will be needed to determine any differences in survivorship for these bearings under normal walking conditions. However, it is now necessary to focus on the reliability of the different bearings under adverse conditions, such as with head loading on the rim of cup, which can occur due to variations in activities, variations in individual patients and variations in surgery. In this regard, there may well be signiﬁcant differences between the different types of bearing materials under adverse conditions. In particular, the metal-on-metal bearings have shown a substantial increase in wear under rim loading conditions, and coupled with the reactivity of metal wear particles, this may cause failures in a number of patients. The ceramic-on-metal and ceramic-on-ceramic bearings are predicted to tolerate these adverse conditions better. We have produced bearing solutions which perform well under standard walking conditions. It is now important for us to focus further research efforts on wear and tribology under a range of different adverse conditions and attempt to further improve reliability and further reduce the currently small number of failures seen under adverse conditions.

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Acknowledgements JF is an NIHR senior investigator. His research is funded by NIHR LMBRU Leeds Musculoskeletal Biomedical Research Unit, through Centre of Excellence in Medical Engineering funded by Wellcome Trust and EPSRC WT 088908/z/09/z, through the Innovation and Knowledge Centre in Regenerative Therapies and Devices funded by EPSRC, BBSRC and TSB and through Orthopaedic Research UK, by the NIH and by ERC.

References 1. Al-Hajjar M, Leslie IJ, Tipper J, Williams S, Fisher J, Jennings LM (2010) Effect of cup inclination angle during microseparation and rim loading on the wear of BIOLOX® delta ceramicon-ceramic total hip replacement. J Biomed Mater Res B Appl Biomater 95:263–268 2. Barbour PSM, Stone MH, Fisher J (2000) A hip joint simulator study using new and physiologically scratched femoral heads with ultra-high molecular weight polyethylene acetabular cups. Proc Inst Mech Eng H 214H:569–576 3. Brown C, Williams S, Tipper JL, Fisher J, Ingham E (2007) Characterisation of wear particles produced by metal on metal and ceramic on metal hip prostheses under standard and microseparation simulation. J Mater Sci Mater Med 18(5):819–827 4. Endo M, Tipper JL, Barton DC, Stone MH, Ingham E, Fisher J (2002) Comparison of wear, wear debris and functional biological activity of moderately crosslinked and non-crosslinked polyethylene in hip prostheses. Proc Inst Mech Eng H 216H:111–122 5. Firkins PJ, Tipper JL, Ingham E, Stone MH, Farrar R, Fisher J (2001) A novel low wearing differential hardness, ceramic-on-metal hip joint prostheses. J Biomech 34:1291–1298 6. Fisher J, Jin Z, Tipper J, Stone M, Ingham E (2006) Tribology of alternative bearings. Clin Orthop Relat Res 453:25–34 7. Fisher J (2011) Bioengineering reasons for the failure of metal on metal hip prostheses. J Bone Joint Surg Br 93B:1001–1005 8. Galvin AL, Tipper JL, Jennings LM, Stone MH, Jin ZM, Ingham E, Fisher J (2007) Wear and biological activity of highly crosslinked polyethylene in the hip under low serum protein concentrations. Proc Inst Mech Eng H 221H:1–10 9. Galvin AL, Jennings LM, Tipper JL, Ingham E, Fisher J (2010) Wear and creep of highly crosslinked polyethylene against cobalt chrome and ceramic femoral heads. Proc Inst Mech Eng H 224H:1175–1183 10. Germain MA, Hatton A, Williams S, Matthews JB, Stone MH, Fisher J, Ingham E (2003) Comparison of the cytotoxicity of clinically relevant cobalt-chromium and alumina ceramic wear particles in vitro. Biomaterials 24:469–479 11. Hatton A, Nevelos JE, Matthew JB, Fisher J, Ingham E (2003) Effects of clinically relevant alumina ceramic wear particles on TNF-a production by human peripheral blood mononuclear phagocytes. Biomaterials 24:1193–1204 12. Ingham E, Fisher J (2000) Biological reactions to wear debris in total joint replacement. Proc Inst Mech Eng H 214 H:21–37 13. Ingham E, Fisher J (2005) The role of macrophages in osteolysis of total joint replacement. Biomaterials 26:1271–1286 14. Leslie I, Williams S, Brown C, Isaac G, Jin Z, Ingham E, Fisher J (2008) Effect of bearing size on the long-term wear, wear debris, and ion levels of large diameter metal-on-metal hip replacements-an in vitro study. J Biomed Mater Res B Appl Biomater 87:163–172 15. Leslie IJ, Williams S, Isaac G, Ingham E, Fisher J (2009) High cup angle and microseparation increase the wear of hip surface replacements. Clin Orthop Relat Res 467:2259–2265 16. Liu F, Galvin A, Jin Z, Fisher J (2011) A new formulation for the prediction of polyethylene wear in artiﬁcial hip joints. Proc Inst Mech Eng 225H:16–24 17. Nevelos J, Ingham E, Doyle C, Streicher R, Nevelos A, Walter W, Fisher J (2000) Microseparation of the centers of alumina-alumna artiﬁcial hip joints during simulator testing produces clinically relevant wear and patterns. J Arthroplasty 15:793–795

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18. Nevelos JE, Ingham E, Doyle C, Nevelos AB, Fisher J (2001) The inﬂuence of acetabular cup angle on the wear of “BIOLOX forte” alumina ceramic bearing couples in a hip joint simulator. J Mater Sci Mater Med 12:141–144 19. Stewart T, Tipper JL, Streicher R, Ingham E, Fisher J (2001) Long-term wear or HIPed alumina on alumina bearings for THR under microseparation conditions. J Mater Sci Mater Med 12:1053–1056 20. Stewart TD, Tipper JL, Insley G, Streicher RM, Ingham E, Fisher J (2003) Long-term wear of ceramic matrix composite materials for hip prostheses under severe swing phase microseparation. J Biomed Mater Res B Appl Biomater 66B:567–573 21. Williams S, Jalai-Vahid D, Brockett CL, Jin Z, Stone MH, Ingham E, Fisher J (2006) Effect of swing phase load on metal-on-metal hip lubrication, friction and wear. J Biomech 39(12):2274–2281 22. Williams S, Butterﬁeld M, Stewart T, Ingham E, Stone MH, Fisher J (2003) Wear and deformation of ceramic-on-polyethylene total hip replacements with joint laxity and swing phase microseparation. Proc Inst Mech Eng H 217H:147–153 23. Williams S, Schepers A, Isaac G, Hardaker C, Ingham E, van der Jagt D, Breckon A, Fisher J (2007) Ceramic-on-metal hip arthroplasties a comparative in vitro and in vivo study. Clin Orthop Relat Res 465:23–32 24. Williams S, Leslie I, Isaac G, Jin Z, Ingham E, Fisher J (2008) Tribology and wear of metalon-metal hip prostheses: inﬂuence of cup angle and head position. United States. J Bone Joint Surg Am 90(3):111–117

How to Treat Failures Related to Articulation

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Luigi Zagra, Luca Bianchi, and Roberto Giacometti Ceroni

2.1 Introduction Wear is the major reason of late failure of total hip arthroplasties [10, 14, 19] as the debris can lead to osteolysis and implant loosening [6–32]. Progressive osteolysis can produce loss of bone, implant failure, and difﬁculties in revision due to bone deﬁciency. All the problems of wear, debris, and loosening arose ﬁrst with polyethylene (PE). The best “treatment” is to prevent failures related to articulation by employing low wear bearing surfaces and monitoring the patients. As a matter of fact, the main problem is not the osteolysis by itself but the progression of osteolysis leading to major bone defects. This progression is not linear but can be exponential (Fig. 2.1), particularly in metal-backed cups due to a stress-shielding phenomenon that has been demonstrated in some studies which have evaluated the bone remodeling around press-ﬁt cups [23, 26]. This area of bone reabsorption can be an easy way where osteolysis progresses. To avoid major damages, patients with joint arthroplasties should be monitored in periodical follow-ups both clinically and radiologically, and in case of progression of osteolysis, they should be revised early (Fig. 2.2). The monitoring of the patients is very important as a ﬁrst radiological sign of osteolysis appears. Anyway, the key point of prevention of failures remains the use of materials with high wear resistance. This is the reason justifying the employment of hard bearings in young patients and of new types of PE, thus reducing wear, but of course it is necessary not to increase other complications related to these materials. It is well known that every coupling has advantages but also its own disadvantages. Standard PE was associated with major wear and osteolysis, even if the problem mainly occurred as a consequence of the sterilization process. In fact, in many cases, the failures were due to the oxidation of PE related to gamma-radiation sterilization in air [21]. There is evidence in the literature [22], and we have personally the same experience, that standard PE, sterilized in ethylene oxide,

L. Zagra (*) • L. Bianchi • R.G. Ceroni Hip department: Istituto Ortopedico Galeazzi IRCCS, Milan, Italy e-mail: [email protected] K. Knahr (ed.), Total Hip Arthroplasty, DOI 10.1007/978-3-642-27361-2_2, © 2012 EFORT

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Fig. 2.1 (a) Male, 50 years old, ceramic 32-mm heads on standard PE showing progression of osteolysis. (b) Clear osteolysis and eccentricity of the head is already visible. (c) In 2 years catastrophic wear

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Fig. 2.2 (a) Female, 62 years old, 7 years postop ceramic 28-mm head on standard PE. The cup is vertical, the head is eccentric; revision was unfortunately not suggested. (b) Four years later, balloon sign and huge metallosis. (c) The ceramic head destroyed the liner and the metal back

shows excellent clinical long-term results. Cross-linked PE (X-PE) is associated with less wear, but the smaller particles produced could potentially be cause of major osteolysis. Breakage of the X-PE liners has been described especially in steep cups with elevated rims [11, 29]. Ceramic on ceramic is the tribology which has demonstrated the lowest wear rate both in experimental and in clinical studies. Moreover, ceramic is biologically inert, so it is the material with the highest biocompatibility, but breakage and noises can occur [1, 5, 15, 18]. Metal on metal has showed a very low wear, but a lot of tissue reactions have been described especially with the introduction of big metal heads. The so-called ARMD (Adverse Reaction to Metal Debris) includes several metal-on-metal effects: ALVAL

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(Aseptic Lymphocyte Dominated Vasculitis Associated Lesions), high ion blood levels, osteolysis, and pseudotumors, and it is a reason of major concern nowadays [3, 4, 24, 31], even if authors have showed good clinical results [7, 27]. Each material with its own properties has its own advantages and disadvantages, and every implant can fail for tribology reasons. The question is: what to do in case of failure? The answer to this question has the aim of helping the orthopedic surgeon in the decision making in case of hip revision, giving some practical suggestions for everyday practice.

2.2 Revision Options The key points for treatment in case of failure that must be considered are: • To identify the origin of the problem in order to avoid to repeat the failure • To verify the implant stability • To evaluate if there is any malposition of the components (particularly relevant is the orientation of the cup) • To optimize the coupling to reduce wear • To restore, when possible, the anatomy of the hip (the center of rotation and the offset) and the bone stock • To treat in the best way the soft tissue damages • To treat and to avoid any impingement Surgical options are: • Liner and/or head exchange in a stable implant • Revision of the cup of the stem of both The aim is to move toward a coupling with a lower wear with a surgery less invasive as possible. On this way, out of the infected cases, there are different decision-making factors that must be considered: • Implant stability: if one of the components is not stable, of course, it must be revised, but sometimes in case of tribology failures, the surgeon has also to replace stable implants which do not work properly or are damaged. Techniques and instrumentations for implant removal should be available in the operating room. • Position of the components: if there is a clear malposition, the replacement of the liner is not enough and the component must be reimplanted in a correct position. The cup orientation remains “crucial”. Vertical or worse both vertical and anteverted cups have to be revised. This cup position can lead to edge loading which causes stripe wear and eventually massive wear also with hard bearings. Malposition can be also the reason of impingement between the neck of the stem and the rim of the cup which is a cause of metal wear, but it is also the mechanism of fracture of the ceramic liner [5, 25]. Also microseparation can lead to rapid wear; insufﬁcient tension of abductors muscles or lack of offset can be the causes [16]. • Implant modularity and availability of the components: in the preoperative planning, the information regarding the prosthesis that has to be revised should be known. Implants of any possible useful standard of all the parts should be available in the operating room at the time of the operation.

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• Damage of the components: if there are major damages of the cup or of the stem at the level of the locking mechanism, they have to be revised even if stable. A ceramic liner cannot be used in a bore of the metal back, thus avoiding a fracture. In these cases, the only salvage procedure can be to cement a PE liner inside the metal back in older patients [13]. A ceramic head, even if of the revision type, but also a metal head cannot be employed if there is a gross damage of the adaptor cone and the stem has to be removed. • Bone stock: the restoration of the bone stock is part of the revision surgery and can, of course, enhance the life of the prosthesis. There are different techniques both in the acetabular and in the femoral side that the surgeon has to know. Revising the different types of coupling, the surgeon can choose among several options, and there are various suggestions for the tribology of the new implant.

2.2.1 Revision of PE It is better to employ X-PE liners or ceramic-on-ceramic coupling in the younger patients, paying attention in avoiding malpositioning. Standard PE “correctly” sterilized can be employed in older patients. In less active patients with stable cups, it can be simpler and bone preserving to cement a liner or better a PE cup in the metal back [13]. In this case, it is advisable to remove the screws or the plugs, when present, and to drill in the holes of the cup in order to improve the locking mechanism of the cement. Then, the metal back should be accurately dried. When a liner is employed instead of a PE cup, it can be scratched if the back is too smooth, and antibiotic-loaded cement is suggested. The head should be changed if possible, especially in case of metal head. The exchange is mandatory in case of damage of the head. If there are no major damages of the adaptor cone, revision ceramic heads or metal heads should be used. Bone graft should be employed in case of acetabular and femoral defects. If the cup and the stem are stable and in correct position and the liner and the head are modular and available, the replacement of the liner and of the head is enough, improving the tribology if possible. If the cup and/or the stem are not stable, they obviously should be revised. X-PE or ceramic-on-ceramic are suggested as bearing surfaces. Bone graft, revision technique, and eventually revision implant may be necessary. If the cup and the stem are stable but malpositioned or there is no possibility of improving the tribology in younger patients, they should be revised: at least the cup together with the head exchange. It is rarely necessary in this case to revise both. The stem has to be changed alone if severely damaged and/or monoblock (without modular head or neck). Cemented stems can be recemented [17, 33] with the cement-within-cement technique in older patients. All the difﬁculties linked to the removal of a cemented or uncemented stable stem can occur. If the cup and the stem are stable and correctly oriented but damaged or nonmodular, they must be revised, improving the tribology. Cup and stem removal and revision techniques are necessary again. In older patients a new liner can be cemented in the stable metal back.

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2.2.2 Revision of Metal on Metal It can be advisable to employ ceramic on X-PE or ceramic on ceramic in the younger patients, again paying attention to malpositioning. Moreover, every metal is different from the other, and they cannot absolutely be mixed from one company to the other. Of course, in case of clear adverse reactions to metal debris, a further metal tribology should be avoided particularly in case of suspected allergy. The surgery procedure has to be aggressive in these cases, removing as much inﬂammatory soft tissues and metallosis as possible. Otherwise, poor outcome has been described [9]. If the stem is stable, the cup is revised and the head is exchanged, better with a ceramic on X-PE or ceramic on ceramic in young patients in addition to the soft tissue treatment. If the stem is not stable or damaged, it has to be revised of course, together with the cup, moving to X-PE or ceramic in case of doubt of ARMD. Again, soft tissue aggressive treatment and revision techniques may be necessary. In case of problems linked to resurfacing such as neck fracture, a conversion to a total hip arthroplasty is usually performed with large metal heads [2]. It is possible when the cup is stable, well oriented and not damaged, and with no signs of ARMD.

2.2.3 Revision of Ceramic on Ceramic In case of aseptic loosening of ceramic on ceramic, X-PE or ceramic can be employed again in young patients. If the ceramic is certainly not broken also metal heads can be used. If the cup is not stable it is revised and a revision ceramic head or a metal head is employed on the stable stem. In a stable cup, a new ceramic liner can be employed if there is the absolute certainty that the metal back is not damaged and if it is correctly positioned. Otherwise, a PE liner is advisable or a revision of the cup should be performed. This same concept is applied in case of squeaking even if moving to a different coupling (X-PE on metal or X-PE on ceramic) is suggested to avoid the risk of recurrence. The main problem with ceramic is in case of breakage, which nowadays can happen mostly to the liner [30]. With hard bearings, orientation is crucial, and ceramic bearing, such as in case of metal on metal, is not forgiving. The mechanics of fracture [5] shows that poor coverage, as it occurs in vertical and anteverted cups, causes edge loading in the upper part of the liner and neck impingement in the inferior rim of the cup. Neck impingement leads to subdislocation and to consequent very small contact on the upper rim, provoking ceramic grain detachment with third body wear and crack propagation with ceramic breakage. Not only the orientation but also the screws can be risky in case of protrusion in the metal back [15]. This is the reason why, with stable press-ﬁt cups, it is suggest to avoid the use of additional screws if not strictly necessary. Moreover, ceramic must be handled with care: any damage of the metal back in the acetabular side and of the adaptor cone of the stem must be avoided. During the liner insertion, attention has to be paid in avoiding

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jamming of the liner in a wrong position. All these even small defects can lead to a ceramic breakage. In case of breakage, an urgent revision must be performed (it is an emergency!) as to avoid the progression of damages. All the visible fragments have to be removed; the soft tissue debridement must be “aggressive” (of the capsule, of the bursa, etc.), adding plenty of washing out. If there is a major damage of the metal back or the cup is malpositioned, it must be revised. If there is a real major damage of the cone of the stem, it must be revised too. In case of minor damage of a well-oriented metal back, a PE liner suitable for the cup can be employed and a revision ceramic head should be employed. Some Authors [28] have reported good results with very aggressive soft tissue removal and metal-on-PE employment, but also catastrophic results have been described as a consequence of massive wear and metallosis of the metal head [8, 20]. Ceramic on ceramic has been suggested in such cases [12, 30]. Even a minimal damage of the shell cannot be tolerated inserting a new ceramic liner. In this situation a revision of the cup is mandatory. Moreover, small residual ceramic fragments can act as third body. PE on ceramic could be the best option or at least the less worse, as in this case the small ceramic fragments are pushed and embedded into the PE liner and the abrasion of the ceramic head is minimal.

2.3 Conclusion Troubles with materials of THA teaches that there is not an ideal solution for every case in tribology and that the surgeon must select the proper indication for each patient considering age, level of activity, bone quality, local anatomy, and risk factors. The correct component position and orientation is critical for each coupling, but for hard bearings, it is less forgiving. This means that, out of the choice of the materials, a proper surgical technique and implant position remain crucial. The correct orientation can be a reason of concern for using approaches or surgical techniques that can be at risk of more difﬁcult positioning such as minimal invasive surgery. From this point of view, the surgeon must take an overall view of pros and cons when introducing new techniques and new materials. Patients need periodical X-rays and clinical evaluation. Monitoring of the cases is an advantage for the clinical outcome of the patient that can be revised early, thus preventing progression of osteolysis, worsening of tribology problems, and major bone defects. But it is also an advantage for the health systems, thus avoiding further more complicated revisions with more expensive devices, more expensive hospitalization, and expensive bone allografts. The surgeon has to take care on the standard X-rays of the appearance and particularly of the progression of osteolysis; of the head position, which should be not eccentric; and of the state of the components. In case of doubt, the CT scan can be helpful for evaluating the integrity of the components of the prosthesis and the position of the head (Fig. 2.3). In rare cases, MR or US for studying soft tissue reactions around the implant can be indicated. The clinical appearance of new noises coming from the articulation is anyway a reason of major concern and must be carefully investigated.

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a

15

b

c

Fig. 2.3 (a) Female, 58 years old, ceramic-on-ceramic coupling with an old sandwich PE liner. (b) Twelve years later, appearance in the X-ray of a new radiological sign suspected for ceramic breakage. (c) CT scan conﬁrms the breakage. The red arrows indicate ceramic fragments

Early revision improving the tribology can prevent catastrophic complications such as loosening or bone loss. It should be considered also in asymptomatic, healthy, and active patients in case of progression of wear and of osteolysis. In these cases, the surgeon should balance advantages and disadvantages of further surgeries avoiding ineffective waiting but also too much aggressive treatments. During the revision, well-ﬁxed implants should be maintained and revised only if strictly necessary such as in case of damaged or malpositioned nonmodular components. The proper tribology should be chosen depending on the patient. Hard low wear-bearing surfaces are indicated for younger and active patients, but also for patients that have shown subjective tendency toward major osteolytic reaction with the previous implant [32]. In any case, the surgeon should not faith only on tribology, but ﬁrst of all in the surgical technique avoiding malposition and impingement, which are two of the main causes of implant failure. Moreover, during revision surgery, the anatomy (mainly center of rotation and offset) and bone stock should be restored when possible. Any malposition that can have a clinical or tribology effect should be corrected and the implant revised. In very severe cases, when risks of instability or of impingement linked to the difﬁculty of reconstructive

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surgery still persist, hard bearings should be employed carefully in order to avoid a failure related to the materials.

References 1. Allain J, Roudot-Thoraval F, Delecrin J, Anract P, Migaud H, Goutallier D (2003) Revision total hip arthroplasty performed after fracture of a ceramic femoral head. A multicenter survivorship study. J Bone Joint Surg Am 85-A(5):825–830 2. Ball ST, Le Duff MJ, Amstutz HC (2007) Early results of conversion of a failed femoral component in hip resurfacing arthroplasty. J Bone Joint Surg Am 89(4):735–741 3. Browne JA, Bechtold CD, Berry DJ, Hanssen AD, Lewallen DG (2010) Failed metal-on-metal hip arthroplasties: a spectrum of clinical presentations and operative ﬁndings. Clin Orthop Relat Res 468(9):2313–2320 4. Clayton RA, Beggs I, Salter DM, Grant MH, Patton JT, Porter DE (2008) Inﬂammatory pseudotumor associated with femoral nerve palsy following metal-on-metal resurfacing of the hip. J Bone Joint Surg Am 90(9):1988–1993 5. Dalla Pria P, Zagra L, Esopi P, Masoni D (2010) Breakage and noises in ceramic on ceramic couplings. Eur Orthop Traumatol 1:53–59 6. Emms NW, Stockley I, Hamer AJ, Wilkinson JM (2010) Long-term outcome of a cementless, hemispherical, press-ﬁt acetabular component: survivorship analysis and dose–response relationship to linear polyethylene wear. J Bone Joint Surg Br 92(6):856–861 7. Girard J, Bocquet D, Autissier G, Fouilleron N, Fron D, Migaud H (2010) Metal-on-metal hip arthroplasty in patients thirty years of age or younger. J Bone Joint Surg Am 92(14):2419–2426 8. Gozzini GA, Schmid C, Dalla Pria P (2002) Massive wear in CoCrMo head following the fracture of an alumina head. Hip Int 12:37–42 9. Grammatopoulos G, Pandit H, Kwon Y-M, Gundle R, McLardy-Smith P, Beard DJ, Murray DW, Gill HS (2009) Hip resurfacings revised for inﬂammatory pseudotumor have a poor outcome. J Bone Joint Surg Br 91-B:1019–1024 10. Huo MH, Brown BS (2003) What’s new in hip arthroplasty. J Bone Joint Surg Am 85-A(9):1852–1864 11. Jacobs CA, Christensen CP, Greenwald AS, McKellop H (2007) Clinical performance of highly cross-linked polyethylenes in total hip arthroplasty. J Bone Joint Surg Am 89(12):2779–2786 12. Kempf I, Semlitsch M (1990) Massive wear of a steel ball head by ceramic fragments in the polyethylene acetabular cup after revision of a total hip prosthesis with fractured ceramic ball. Arch Orthop Trauma Surg 109(5):284–287 13. Khanuja HS, Aggarwal A, Hungerford MW, Hungerford DS, Jones LC, Mont MA (2010) Cementing polyethylene liners into non-modular acetabular components in revision total hip arthroplasty. J Orthop Surg 18(2):184–188 14. Learmonth ID (2003) Biocompatibility: a biomechanical and biological concept in total hip replacement. Surgeon 1(1):1–8 15. Lee SC, Jung KA, Nam CH, Kim TH, Ahn NK, Hwang SH (2010) Acetabular screw headinduced ceramic acetabular liner fracture in cementless ceramic-on-ceramic total hip arthroplasty. Orthopedics 33(5). doi:10.3928/01477447-20100329-30 16. Leslie IJ, Williams S, Isaac G, Ingham E, Fisher J (2009) High cup angle and microseparation increase the wear of hip surface replacements. Clin Orthop Relat Res 467(9):2259–2265 17. Lieberman JR, Moeckel BH, Evans BG, Salvati EA, Ranawat CS (1993) Cement-withincement revision hip arthroplasty. J Bone Joint Surg 75 B:869–871 18. Lusty PJ, Watson A, Tuke MA, Walter WL, Walter WK, Zicat B (2007) Wear and acetabular component orientation in third generation alumina-on-alumina ceramic bearings: an analysis of 33 retrievals [corrected]. J Bone Joint Surg Br 89(9):1158–1164

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19. Mäkelä KT, Eskelinen A, Pulkkinen P, Paavolainen P, Remes V (2011) Results of 3,668 primary total hip replacements for primary osteoarthritis in patients under the age of 55 years. Acta Orthop 82(5):521–529 20. Matziolis G, Perka C, Disch A (2003) Massive metallosis after revision of a fractured ceramic head onto a metal head. Arch Orthop Trauma Surg 123(1):48–50 21. McKellop HA, Campbell P, Park SH, Schmalzried TP, Grigoris P, Amstutz HC, Sarmiento A (1995) The origin of submicron polyethylene wear debris in total hip arthroplasty. Clin Orthop Relat Res 311:3–20 22. McKellop HA, Shen FW, Lu B, Campbell P, Salovey R (2000) Effect of sterilization method and other modiﬁcations on the wear resistance of acetabular cups made of ultra-high molecular weight polyethylene. A hip-simulator study. J Bone Joint Surg Am 82-A(12):1708–1725 23. Mueller LA, Voelk M, Kress A, Pitto RP, Schmidt R (2007) An ABJS best paper: progressive cancellous and cortical bone remodeling after press-ﬁt cup ﬁxation: a 3-year followup. Clin Orthop Relat Res 463:213–220 24. Murray DW, Grammatopoulos G, Gundle R, Gibbons CL, Whitwell D, Taylor A, Glyn-Jones S, Pandit HG, Ostlere S, Gill HS, Athanasou N, McLardy-Smith P (2011) Hip resurfacing and pseudotumour. Hip Int 21(3):279–283 25. Onda K, Nagoya S, Kaya M, Yamashita T (2008) Cup-neck impingement due to the malposition of the implant as a possible mechanism for metallosis in metal-on-metal total hip arthroplasty. Orthopedics 31(4):396 26. Pitto RP, Bhargava A, Pandit S, Walker C, Munro JT (2008) Quantitative CT-assisted osteodensitometry of femoral adaptive bone remodelling after uncemented total hip arthroplasty. Int Orthop 32(5):589–595 27. Saito S, Ishii T, Mori S, Hosaka K, Ootaki M, Tokuhashi Y (2010) Long-term results of metasul metal-on-metal total hip arthroplasty. Orthopedics 11;3(8):3 28. Sharma V, Ranawat AS, Rasquinha VJ, Weiskopf J, Howard H, Ranawat CS (2010) Revision total hip arthroplasty for ceramic head fracture: a long-term follow-up. J Arthroplasty 25(3):342–347 29. Tower SS, Currier JH, Currier BH, Lyford KA, Van Citters DW, Mayor MB (2007) Rim cracking of the cross-linked longevity polyethylene acetabular liner after total hip arthroplasty. J Bone Joint Surg Am 89(10):2212–2217 30. Traina F, Tassinari E, De Fine M, Bordini B, Toni A (2011) Revision of a ceramic hip for fractured ceramic components. J Bone Joint Surg Am 93(24):1471–1479. 31. Willert HG (2005) Metal-on-metal bearings and hypersensitivity in patients with artiﬁcial hip joints. A clinical and histomorphological study. J Bone Joint Surg Am 87(1):28–36 32. Willert HG, Bertram H, Buchhorn GH (1990) Osteolysis in alloarthroplasty of the hip. The role of ultra-high molecular weight polyethylene wear particles. Clin Orthop Relat Res 258:95–107 33. Young J, Vallamshetla VR, Lawrence T (2008) The polished tri-tapered stem for cement-incement revision hip arthroplasty, a reliable and reproducible technique? Hip Int 18(4):272–277

Part II Polyethylene Articulations

Oxidation Prevention with Vitamin E in a HXLPE Isoelastic Monoblock Pressfit Cup: Preliminary Results

3

Martin Beck, Daniel Delfosse, Reto Lerf, Roland Becker, Gary French, Lutz Hollmann, Karl Knahr, Helmy Naeder, Eric Meijer, Philipp Rehbein, Joseph Baines, Vincent Steenmeijer, and Arthur de Gast

M. Beck (*) Clinic for Orthopaedic Surgery, Luzerner Kantonsspital, Lucerne, Switzerland e-mail: [email protected]

H. Naeder Orthopaedic Department, Bürgerspital Solothurn, Solothurn, Switzerland

D. Delfosse (*) • R. Lerf Innovation Group, Mathys Ltd Bettlach, Bettlach, Switzerland e-mail: [email protected]

E. Meijer Orthopaedic Department, Ziekenhuis Amstelland, Amstelveen, The Netherlands

R. Becker Orthopàdic und Unfallchirwgic, Städtisches Klinikum Brandenburg GmbH, Brandenburg, Germany

P. Rehbein Orthopaedic Department, St. Josefs-Hospital, Wiesbaden, Germany

G. French Orthopaedic Department, Ormiston Orthopaedics, Manukau, New Zealand

J. Baines Orthopaedic Department, Golden Jubilee National Hospital, Clydebank, Scotland

L. Hollmann Orthopaedic Department, Streekziekenhuis Koningin Beatrix, Winterswijk, The Netherlands

V. Steenmeijer Orthopaedic Department, Ziekenhuis Bronovo, Den Haag, The Netherlands

K. Knahr Orthopaedic Department, Orthopädisches Spital Speising GmbH, Vienna, Austria

A. de Gast Orthopaedic Department, Diakonessenhuis Utrecht/Zeist, Utrecht, The Netherlands

K. Knahr (ed.), Total Hip Arthroplasty, DOI 10.1007/978-3-642-27361-2_3, © 2012 EFORT

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3.1 Introduction With increasing life expectancy and activity of patients, prosthetic bearing with very low wear rates are getting more and more important. Although ceramic-on-ceramic bearings offer the least discernible wear rate this advantage is to some extent reduced by the danger of a rare but devastating fracture of the ceramic liner or head and the occurrence of squeaking [1–3]. Metal-on-metal bearings have an increasingly bad reputation due to adverse reaction to metal wear and ions, especially when used with large-diameter heads [4–7]. Therefore, it is of major interest to further improve polyethylene in order to decrease wear and increase the lifetime of such an implant. The lifetime of ultra-high molecular weight polyethylene (UHMWPE) implants are limited by wear and oxidative degeneration. Accelerated PE wear, delamination and in rare cases even component fractures are consequences of the embrittlement of the PE due to oxidation. Wear-produced particles are in general biologically active and may induce osteolysis. As threshold of PE wear rate, below which osteolysis is rarely observed, is postulated to be less than 0.1 mm/year [8]. Thus, improving the clinical behaviour of UHMWPE means reduction of wear particles. Highly cross-linked polyethylene (HXLPE) has shown low wear in hip simulator tests. These results lend hope that the particle generation may lie below the threshold that leads to osteolysis. Clinically, meta-analyses and mid-term results up to 10 years are available now [9, 10], and these show a consistent reduction of wear by a factor of two to eight times compared to standard UHMWPE. There is, however, still some concern due to loss of material toughness and in vivo oxidation [11]. In order to improve the materials’ properties for wear and longevity, a new generation of crosslinked polyethylene was developed that is protected against oxidation by a small amount of an antioxidant, alpha-tocopherol, commonly known as vitamin E [12–14]. The ﬁrst two vitamin-doped HXLPE materials were clinically introduced for hip arthroplasty in 2007 as E1-poly (Biomet Inc, Warsaw, IN) and in September 2009, as an isoelastic soft-bearing cup, the RM Pressﬁt vitamys (Mathys Ltd Bettlach, Switzerland; Fig. 3.1). But so far, no clinical results have been reported in the peer-reviewed literature. The introduction of a new implant material is not without risk, as too many incidences in the past have shown. Despite apparently good preclinical test results, some materials failed in clinical practice with detrimental outcomes for the patient. In order to reach a higher level of safety, a new approach for the preclinical testing has been taken. A series of worst-case scenarios were developed and tested accordingly to answer questions such as: What will happen to the material over a long implantation time, e.g. 20 or more years? With the ﬁrst implantation of the RM Pressﬁt vitamys cup, a prospective, multi-centre study was initiated. This paper is the ﬁrst to report on the clinical performance of vitamin E-blended HXLPE hip implants.

3.2 Material and Methods The vitamys material was made in-house at Mathys Ltd Bettlach by a proprietary manufacturing process (Patents WO0049079 and EP1161489) using GUR 1020 powder from Ticona GmbH, Kelsterbach/Germany and alpha-tocopherol (vitamin E) in Ph EUR quality

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Fig. 3.1 The RM Pressfit vitamys cup

from Merck KGaA, Darmstadt/Germany; 0.1 wt.-% of vitamin E was added before crosslinking at 100 (±10) kGy by gamma-irradiation. The ﬁnal sterilisation step was done with gas plasma. For comparison, standard UHMWPE material and implants were included. These are cut out of sintered GUR 1020 plates, machined to their ﬁnal shape and gamma-sterilised in inert atmosphere at 30 kGy. Accelerated ageing of UHMWPE and vitamys materials was performed according to ASTM 2003-02 in pressurised oxygen at elevated temperature. Therefore, the samples were placed in a Membar pure pressure vessel 304SS (Membar pure, Germany) without contact of the relevant surfaces to other samples or the wall. The pressure vessel was ﬁlled with 100% oxygen. The accelerated ageing was done at 5 at oxygen and 70°C according to the ASTM 2003-02 standard procedure. The time a sample spends in accelerated ageing can be translated to an approximate time of in vivo oxidative loading [15]. Fourteen days of accelerated ageing corresponds to 10 years in vivo; 60 days amount to more than 40 years in vivo.

3.2.1 Mechanical Testing The mechanical properties were assessed by tensile testing of UHMWPE and vitamys material, both in pristine and artiﬁcially aged condition. Tests were carried out with a

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Zwick materials testing machine 1474 UBM (Zwick GmbH & Co. KG, Ulm, Germany), using tensile testing specimens according to DIN 53594, type S3A and ASTN D638, type IV. Preloading was set to 1 MPa, loading speed to 100 mm/min. Yield strength (YS), ultimate tensile strength (UTS) and elongation at break (EAB) were recorded for a minimum of ﬁve test specimens per condition.

3.2.2 Hip Simulator Testing Testing according to ISO 14242-1 was conducted in a servo-hydraulic six-station hip simulator (Endolab, Thansau/Rosenheim and Germany) at a temperature of 37 ± 1°C. All tests were run for 3 million cycles, corresponding to the requirement of ISO 14242, based on N = 3 tests per condition. The test ﬂuid of this study was based on bovine serum (newborn calf serum, New Zealand, GIBCO Invitrogen Corporation, Lot 8097790) diluted with deionised water. The ﬂuid was not prepared according to ISO 14242-1 but followed the recipe of Endolab. A protein concentration of 30 g/l instead of the 17–19 g/l suggested in the ISO standard was selected because the synovial ﬂuid of artiﬁcial hip joints was shown to contain protein concentrations between 20 and 40 g/l, with an average at around 30 g/l [16, 17]. Sodium azide and 3 g/l EDTA were added to inhibit bacterial growth and to bind metallic ions. To remove bacteria from the test ﬂuid, it was passed through 0.2-mm ﬁlters. Test and reference samples were pre-soaked in the testing liquid at 37°C for 7 days. Two days before starting the hip simulation, the test samples were embedded with the chosen inclination (between 30° and 65°). The load and motion simulate the conditions while walking. The same load proﬁle was applied onto the reference samples, but no motion was applied. After each 500,000 cycles, the testing chamber was taken apart and cleaned, and the inlays were cleaned and conditioned according to the recommendations of ISO 14242-2 before weighing with an accuracy of 0.01 mg (Mettler Toledo AX205, Greifensee, Switzerland). The wear of each inlay was calculated taking the difference before and after the wear test and corrected for the amount of soaking of the reference sample: After weighing, the reassembled testing chambers were ﬁlled with fresh test ﬂuid and installed in another measuring station of the hip simulator.

3.2.2.1 Materials Used Heads: 28-mm metallic heads made of CoCr alloy and 28- and 36-mm ceramic heads made of alumina (Bionit, Mathys Ltd Bettlach, Switzerland) were employed in the tests reported here. For the artiﬁcially aged materials, 28-mm CoCr heads were used. Cups: Inlays for the seleXys cup size 50/EE (Mathys Ltd Bettlach, Switzerland) and test samples corresponding to the RM Pressﬁt cup size 52 (Mathys Ltd Bettlach, Switzerland), but manufactured without Ti-particle coating, were used. Both types of cup samples were available in UHMWPE and vitamys. The UHMWPE was manufactured from GUR 1020 plates and sterilised under absence of oxygen with 25- to 38-kGy gamma-irradiation.

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3.2.3 Clinical Documentation With the ﬁrst RM Pressﬁt vitamys implantation, a prospective multi-centre study started. Surgeries were carried out in ten European and one New Zealand clinics. The ﬁrst patient was operated in September 2009; patient recruitment is still ongoing. So far, 553 cases (528 patients) with 25 bilateral cases are included; 60% are female patients. The average age at surgery was 68.0 years (range, 19.0–93.1), with a mean BMI of 27.3 kg/m2 (14.6– 46.9). The patients are clinically and radiologically followed up after 6–12 weeks; 6, 12 and 24 months; and thereafter for long-term results. Standardised documentation of surgery and postoperative follow-up is performed. The study data is collected on the MEMdoc (University of Berne, Switzerland) online database. The most frequent diagnosis for total hip replacement was primary osteoarthrosis (83.5%); 8.5% were treated for secondary osteoarthrosis, 2.9% for avascular necrosis of the femoral head, 2.5% for femoral neck fracture, 1.6% for congenital dysplasia and 1% for other indications. Slightly more patients needed a total hip replacement on the right hip (52.3%). The most common surgical approach was the posterolateral approach (38.9%); in 22.4%, a transgluteal; in 21.7%, an anterior; and in 17.0%, an anterolateral approach was done. One third of the approaches were labelled minimally invasive. In only ﬁve cases (1%), additional screw ﬁxation of the cup was necessary to achieve a sufﬁcient primary ﬁxation. The RM Pressﬁt vitamys cup is available for articulation with 28-, 32- and 36-mm femoral head diameters. The smallest cup with a 36-mm femoral head has an outer diameter of 52 mm. This size was the most frequently used with 22% of all cases. A 36-mm head was implanted in 60% of the cases; a 32-mm, in 28%; and a 28-mm, in 12%. Of all surgeries, 97.5% were done using a ceramic femoral head.

3.3 Results 3.3.1 Mechanical Properties Table 3.1 shows the results of tensile testing. It is apparent that despite the cross-linking process for the vitamys material, there is no signiﬁcant difference between the standard UHMWPE and vitamys in terms of yield strength (YS), ultimate tensile strength (UTS) and elongation at break (EAB). The vitamys material fulﬁls the mechanical requirements for UHMWPE type 1 according to the ISO standard 5834-2:2006. Moreover, even after accelerated testing for 60 days, the mechanical properties remain high. The EAB even shows an increase with ageing. This is in complete contrast to the aged UHMWPE samples. They could not be tested due to their brittleness because the specimens failed already during the set-up of the tensile test. Figure 3.2 visualises the difference in brittleness after accelerated ageing for the tested materials.

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Table 3.1 Mechanical properties of UHMWPE and vitamys obtained by tensile testing YS (MPa)

UTS (MPa)

EAB (%)

UHMWPE gamma-sterilised, 23.9 ± 0.3 unaged

40.6 ± 6.9

456 ± 113

UHMWPE gamma-sterilised, n.a. aged 29 days

n.a.

n.a.

Vitamys, irradiated at 100 kGy, unaged

22.8 ± 0.4

39.3 ± 5.5

391 ± 80

Vitamys, irradiated at 100 kGy, aged 60 days

23.9 ± 0.3

40.4 ± 4.4

509 ± 58

ISO 5834-2:2006, requirements for type 1

³21.0

³35.0

³300

Fig. 3.2 Appearance of gamma-sterilised UHMWPE (left) and vitamys (right) after accelerated ageing for 29 days, respectively 60 days (corresponding to 20 years, respectively 40 years in vivo) and tensile testing. The brittle nature of the aged UHMWPE samples is shown in contrast to the highly plastic deformation of the aged vitamys samples

3.3.2 Wear Rates

3.3.2.1 Influence of the Degree of Cross-Linking The wear rates are extremely sensitive to the degree of cross-linking, i.e. the amount of gamma-irradiation used, up to a dose of around 100 kGy after which the decrease of wear rates tapers off. This is shown in Fig. 3.3 where the standard (also called “moderately cross-linked”) UHMWPE can be found at an irradiation dose of 30 kGy used for sterilisation. Materials treated with higher amounts of gamma-irradiation are coined “highly crosslinked polyethylene” (HXLPE). The vitamys material is treated with a dose of 100-kGy

Oxidation Prevention with Vitamin E in a HXLPE Isoelastic Monoblock Pressﬁt Cup

Fig. 3.3 Wear rate as a function of gamma-irradiation dose for two different head diameters. The standard UHMWPE is gammasterilised with a dose of 30 kGy, whereas vitamys is cross-linked with a dose of 100 kGy

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50 Wear rate [mg/Mcycle]

3

Head size 36 mm

40

Head size 28 mm 30 20 10 0 0

20

60 40 80 Cross-linking dose [kGy]

100

120

gamma-irradiation. The wear rate of this vitamin-doped HXLPE was found to be at least seven times lower than the wear rate of gamma-sterilised standard UHMWPE.

3.3.2.2 Influence of the Head Material and Diameter Using a ceramic head instead of a CoCr head did not alter the wear rate measured in the hip simulator tests for UHMWPE and vitamys. Increasing the diameter of the ball heads, however, leads to a signiﬁcant raise in wear rates of gamma-irradiated UHMWPE as measured in the hip simulator test (Fig. 3.3). The difference in wear rate seen with moderately cross-linked UHMWPE disappears when higher levels of cross-linking are reached. For the vitamys material, a 36-mm head results in a wear rate that is as the same low level as with a 28-mm head.

3.3.2.3 Influence of the Accelerated Ageing The high sensitivity of gamma-sterilised UHMWPE to oxidation is depicted clearly when comparing hip simulator wear rates of unaged and aged UHMWPE (Fig. 3.4). The wear rate is increased nearly tenfold after 29 days of artiﬁcial ageing according to ASTM 200302 (due to the rapid head penetration, the test had to be stopped after three million cycles). Again, the vitamys material showed a completely different and much more benign behaviour compared to the UHMWPE material. Even when vitamys was aged for periods up to 60 days, the wear rates remained at the same low level.

3.3.3 Clinical Follow-up A number of intra- and early postoperative complications were noted. In one patient, the cup tilted during reduction of the hip. The cup was repositioned in correct position and the hip reduced without cup tilting. During hospital stay, however, the cup tilted again. It was re-orientated and ﬁxed with two additional screws 3 days after primary

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M. Beck et al. Wear rate (mg/Mcycle) 350 300 250 200 150 100 50 0 UHMWPE unaged

UHMWPE aged 29 d

vitamys unaged

vitamys aged 60 d

Fig. 3.4 Comparison of the wear rate of UHMWPE and vitamys in unaged condition and after artiﬁcial ageing for 29 days, respectively 60 days (corresponding to 20 years, respectively 40 years in vivo)

Fig. 3.5 Comparison of the preoperative values and at 1-year follow-up

10

pre-op 1-year FU

8 6 4 2 0 VAS satisfaction

VAS rest pain

VAS load pain

HHS (/10)

implantation. At 1-year follow-up, the cup showed stable radiographic integration, and the patient is satisﬁed and without pain. During hospital stay, one patient sustained a posterior hip dislocation, treated with a closed reduction; one patient sustained a femur fracture ﬁxed with a wire, and two patients had fractures of the greater trochanter. So far a total of 658 postoperative examinations were performed; a 1-year follow-up is available for 164 cases. Four patients deceased during follow-up; two patients missed the planned examination for personal reasons, and one patient could not be contacted. All patients showed stable implant ﬁxation during the last follow-up performed. There was no sign of early loosening of the cup. During follow-up, one isolated stem revision had to be performed after a periprosthetic fracture 20 days postoperative. Two weeks postoperatively, one patient sustained a hip dislocation, which spontaneously reduced. On a visual analogue scale (VAS), the satisfaction improved from preoperative 2.9 (range, 0.0–10.0) to 9.3 (0.0–10.0) one year after surgery (Fig. 3.5). The VAS for rest and load pain improved from preoperative 4.2 (0.0–10.0) to 0.3 (0.0–7.0) and from 7.1 (0.0–10.0) to 0.6 (0.0–7.0) one year postoperative, respectively. Before surgery, the mean HHS was 55.0 points (4.0–95.0); 6–12 weeks after surgery, it increased to 88.3 points (38.0–100.0), and after 1 year, to 95.9 points (50.0–100.0). Preoperatively, the

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Oxidation Prevention with Vitamin E in a HXLPE Isoelastic Monoblock Pressﬁt Cup

29

mean ﬂexion was 83.5° (0.0–130.0); after 6–12 weeks, 93.2° (10.0–120.0) and 98.2° (50.0–130.0) 1 year after surgery.

3.4 Discussion 3.4.1 Mechanical Properties The protection of UHMWPE by small additions of vitamin E has two beneﬁcial effects on the mechanical properties. Firstly, the re-melting process that is necessary for ﬁrstgeneration HXLPE can be avoided and with it the inherent decrease in toughness. Vitamin E-blended material, when processed carefully, exhibits similar mechanical properties to gamma-irradiated UHMWPE. Secondly, the high oxidation resistance of vitamin E-blended materials has the beneﬁt that the mechanical properties remain at the same level as the pristine material even after decades of shelf life or in vitro implantation time. The implant will neither turn brittle nor fragile over its life span.

3.4.2 Wear Rates The wear rate of the vitamin-doped HXLPE was found to be at least seven times lower than the wear rate of standard gamma-sterilised UHMWPE. Contrary to UHMWPE, the wear rate of vitamys remained at a constant low level when different ball head materials and head sizes were employed or even after the polymer was subjected to accelerated ageing equivalent to more than 40 years in vivo. These results give faith in the novel material because it seems to be very robust against any form of oxidative attack that may occur during shelf life or in vivo. The wear rate of vitamys is therefore predicted to remain at the same low level over its lifetime inside a patient. The rapid increase of wear rate with artiﬁcial ageing of the gamma-sterilised UHMWPE appears quite extreme and warrants further investigation. It may well be that the artiﬁcial ageing protocol according to ASTM 2003-02 simulates a condition that is more severe than effectively experienced during shelf life or in vivo. But the results clearly demonstrate the risk that over time, a non-protected UHMWPE may become more and more brittle, and when this happens, accelerating wear rates are inevitable.

3.4.3 Clinical Follow-up The principles of this type of monoblock cup with its isoelastic property and the thin Ti-particle coating is a well-documented and proven concept. Excellent long-term survival rates of the RM Classic cup have been published; survival rates with acetabular revision

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for aseptic loosening as endpoint were 98% after 14 years and 94% after 20 years [18, 19]. In both studies, a notable number of cups had to be revised between 14 and 16 years after implantation due to the radiographic appearance of eccentric wear and osteolysis. It is important to note, however, that these events did not result in cup loosening. At the time of revision, these cups were stably anchored – an indication of the excellent osseointegration of the Ti-particle coating. For cups articulating with ceramic heads, a lower wear rate and a signiﬁcantly higher survival rate was consistently found when compared to cups articulating with metal heads. For patients with congenital dysplasia, the RM Classic cup survival rate after 20 years was 100% [20]. The RM Pressﬁt vitamys cup has two main advantages over the RM Classic or the RM Pressﬁt cup with standard UHMWPE: a better wear resistance due to the use of a HXLPE material and a lower risk of dislocation due to the possibility to employ larger heads. The increased wear resistance should theoretically lead to less osteolysis and therefore to a better long-term outcome. On the other hand, a larger head increases range of motion, decreases the risk of dislocations and hence may lead to a better short-term outcome. It is interesting to note that the distribution of head sizes changed indeed signiﬁcantly from the RM Pressﬁt cup with standard UHMWPE. The smallest RM Pressﬁt vitamys cup size available with a 36-mm ball head is used more often than the Gaussian distribution would indicate. It therefore seems that at least a number of surgeons aim to lower the dislocation risk by employing larger head sizes than previously possible, thus even sacriﬁcing some of the acetabular bone stock. The ﬁndings of the present study are very promising. So far, with the exception of one early failure during hospital stay, no further cup revision or major cup-related complication was reported. All cups show stable integration on radiographs. There is now some patience required to prove the durability of this novel material and to show a signiﬁcant improvement over the mid- and long-term results of the existing elastic cups with standard UHMWPE.

3.5 Conclusions The protection of HXLPE with vitamin E leads to excellent oxidation resistance. It has a number of important beneﬁts for the material properties, most importantly the effective prevention of any loss of toughness over the entire life span of the implant. It can therefore be assumed that an implant made of vitamin E-blended HXLPE will not only have a very low wear rate initially but retain its mechanical and tribological properties over periods of 40 years or more. An elastic cup such as the RM Pressﬁt vitamys includes interesting and unique features such as high elasticity (no stress shielding) and high ageing and wear resistance combined with clinically proven biological anchorage – making it theoretically extremely suitable for the young and active patient. Its ﬁrst clinical results are encouraging, but of course much longer clinical follow-up is needed.

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References 1. Stafford GH, Islam SU, Witt JD (2011) Early to mid-term results of ceramic-on-ceramic total hip replacement: analysis of bearing-surface-related complications. J Bone Joint Surg Br 93(8):1017–1020 2. Affatato S, Traina F, Toni A (2011) Microseparation and stripe wear in alumina-on-alumina hip implants. Int J Artif Organs 34(6):506–512 3. Stanat SJ, Capozzi JD (2011) Squeaking in third- and fourth-generation ceramic-on-ceramic total hip arthroplasty, meta-analysis and systematic review. J Arthroplasty [Epub ahead of print] doi: 10.1016/j.arth.2011.04.031 4. Aroukatos P, Repanti M, Repantis T et al (2010) Immunologic adverse reaction associated with low-carbide metal-on-metal bearings in total hip arthroplasty. Clin Orthop Relat Res 468(8):2135–2142 5. Catelas I, Wimmer MA (2011) New insights into wear and biological effects of metal-on-metal bearings. J Bone Joint Surg Am 93(Suppl 2):76–83 6. Langton DJ, Jameson SS, Joyce TJ et al (2010) Early failure of metal-on-metal bearings in hip resurfacing and large-diameter total hip replacement: a consequence of excess wear. J Bone Joint Surg Br 92(1):38–46 7. Langton DJ, Jameson SS, Joyce TJ et al (2011) Accelerating failure rate of the ASR total hip replacement. J Bone Joint Surg Br 93(8):1011–1016 8. Dumbleton JH, Manley MT, Edidin AA (2002) A literature review of the association between wear rate and osteolysis in total hip arthroplasty. J Arthroplasty 17(5):649–661 9. Kurtz SM, Gawel HA, Patel JD (2011) History and systematic review of wear and osteolysis outcomes for ﬁrst-generation highly crosslinked polyethylene. Clin Orthop Relat Res 469(8):2262–2277 10. Kuzyk PRT, Saccone M, Sprague S et al (2011) Cross-linked versus conventional polyethylene for total hip replacement. J Bone Joint Surg Br 93(5):593–600 11. Currier BH, Van Citters DW, Currier JH et al (2010) In vivo oxidation in remelted highly cross-linked retrievals. J Bone Joint Surg Am 92(14):2409–2418 12. Lerf R, Zurbrügg D, Delfosse D (2010) Use of vitamin E to protect cross-linked UHMWPE from oxidation. Biomaterials 31(13):3643–3648 13. Oral E, Moratoglu OK (2011) Vitamin E diffused, highly crosslinked UHMWPE – a review. Int Orthop 35(2):215–223 14. Bracco P, Oral E (2011) Vitamin E-stabilized UHMWPE for total joint implants – a review. Clin Orthop Relat Res 469(8):2286–2293 15. Zurbrügg D, Abt NA (2003) Comparison between in vivo aging, shelf and accelerated aging of UHMWPE based on the theory of oxidation kinetics. Poster at 18th European conference on biomaterials, Stuttgart, 1–4 Oct 2003 16. Noordin S, Schmalzried TP, Campbell P et al (1997) Synovial ﬂuid from patients with prosthetic joint arthroplasty: protein concentration and in vivo wear of polyethylene. In: Transactions of the 43rd annual meeting of the Orthopaedic Research Society, San Francisco, 1997, vol 22, p 769 17. Saari H, Santavirta S, Nordstrom D et al (1993) Hyaluronate in total hip replacement. J Rheumatol 20(1):87–90 18. Pakvis D, Biemond L, van Hellemondt G et al (2010) A cementless elastic monoblock socket in young patients: a ten to 18-year clinical and radiological follow-up. Int Orthop 35(10):1445–1451 19. Ihle M, Mai S, Pﬂuger D et al (2008) The results of the titanium-coated RM acetabular component at 20 years: a long-term follow-up of an uncemented primary total hip replacement. J Bone Joint Surg Br 90(10):1284–1290 20. Ihle M, Mai S, Siebert WE (2010) Treatment for acetabular dysplasia using the uncemented RM acetabular component – a 20 year follow-up. Hip Int 20(1):94–101

In Vitro Wear Testing of Conventional Versus Sequentially Cross-Linked Polyethylene Liners in Combination with Diﬀerent Sizes of Ceramic Femoral Heads

4

Carmen Zietz, Andreas Fritsche, Lars Middelborg, Wolfram Mittelmeier, and Rainer Bader

4.1 Introduction The prevalent cause of implant failure after total hip replacement (THR) is aseptic loosening caused by wear debris, i.e. mainly particles from ultra-high molecular weight polyethylene (UHMWPE) [9, 15, 25]. Bone resorption at the implant adjacent area occurs due to the access of these particles to the periprosthetic tissue where they lead to inﬂammatory reactions [8, 23]. Therefore, improvement of the wear behaviour of the articulating bearing and reduction of wear debris between the UHMWPE liner and the femoral head is essential for increased life expectancy of artiﬁcial hip joints. Cross-linking of the UHMWPE material is one attempt to reduce wear particle release at the articulating surface [11]. For several years, various cross-linked polyethylene (X-PE) materials have been used in THR [36]. Different in vitro simulator tests demonstrate the wear reduction using X-PE [20], and ﬁrst clinical outcome studies show promising results [7, 21, 28, 35]. Beside wear, dislocation and impingement are serious problems in THR. The use of larger femoral head sizes can decrease these risks by an improved range of motion in comparison to smaller head size [6, 12]. However, the increasing diameter of femoral head is associated with an increased wear rate [29, 30, 38]. Hence, by using X-PE, the application

C. Zietz (*) • A. Fritsche • L. Middelborg • W. Mittelmeier • R. Bader Department of Orthopaedics, University of Rostock, Doberaner Str. 142, Rostock D-18057, Germany e-mail: [email protected] K. Knahr (ed.), Total Hip Arthroplasty, DOI 10.1007/978-3-642-27361-2_4, © 2012 EFORT

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of larger femoral heads could be possible without increased wear rates [31]. Furthermore, the lower thickness of the X-PE liner has to be examined critically because of the derogation of mechanical properties caused by cross-linking [2, 10, 22]. The aim of the present experimental study was to evaluate and to compare the wear of conventional UHMWPE (C-UHMWPE) and sequentially X-PE acetabular liners in combination with different ceramic femoral head sizes.

4.2 Materials and Methods The C-UHMWPE liners were made of ram-extruded GUR 1050 resin, packed in a nitrogen atmosphere and gamma irradiated at 3 MRad for sterilisation (N2Vac, Stryker GmbH & Co. KG, Duisburg, Germany) [32]. The sequentially cross-linked (X3™) liners were made of compression-moulded GUR 1020 resin sheets which were irradiated with 3 MRad followed by annealing the sheets below the melt temperature. The irradiation and annealing process were repeated three times alternately. After machining, the implants (X3™, Stryker GmbH & Co. KG, Duisburg, Germany) were gas plasma sterilised [17]. Wear testing was performed for ﬁve million (Mio.) load cycles using three C-UHMWPE liners (N2Vac) and three sequentially cross-linked X3™ liners combined with 28-mm alumina ceramic ball heads (BIOLOX®forte, CeramTec AG, Plochingen, Germany) and Trident® PSL acetabular cups (Stryker GmbH & Co. KG, Duisburg, Germany). Furthermore, in total six X3™ liners, three with an internal diameter of 36 mm and three with 44 mm were combined with the corresponding alumina ceramic heads (BIOLOX®forte, CeramTec AG, Plochingen, Germany). For the liners, a wall thickness of >9, 5.9 and 3.8 mm resulted for 28, 36 and 44 mm femoral heads, respectively. The used liners and femoral heads are shown in Fig. 4.1. A six-station hip wear simulator according to ISO 14242-1 (EndoLab GmbH, Rosenheim, Germany) was used to carry out standard wear tests. Additionally, two loaded reference stations were used to control liquid absorption of the UHMWPE liners. The wear tests were conducted in temperature- and ﬂuid level-controlled test chambers at 37 ± 2°C for 5 Mio. load cycles at a frequency of 1 Hz. Axial load and angles (ﬂexion, adduction, rotation) of the specimens inside the hip simulator were conformed to ISO 14242-1 as recommended kinematics for the hip joint. The specimens were changed periodically between the six running stations each 0.5 Mio. cycles. Calf serum (PAA Laboratories GmbH, Pasching, Austria) with a protein concentration of 20 g/l was used as lubricant for the tests. Sodium acid (NaN3) and ethylenediamine tetraacetic acid (EDTA) were added to prevent microbiological contamination and calcium phosphate precipitation, respectively. Every 0.5 Mio. cycles, the lubricant was changed and the wear of the liners was determined gravimetrically using a high-precision balance (Sartorius ME235S, Sartorius AG, Göttingen, Germany) up to 5 Mio. cycles. Statistical signiﬁcance between groups was calculated with ONEWAY ANOVA (Post Hoc LSD) using SPSS 15.0 for Windows (SPSS Inc., Chicago, USA). Data were presented as mean value ± standard deviation and a probability value of p < 0.05 was considered signiﬁcant.

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Polyethylene Head size

N2Vac, X3TM

X3TM

28 mm

36 mm

X3TM 44 mm

Fig. 4.1 Test specimens: acetabular liner out of conventional UHMWPE (N2Vac) and sequentially cross-linked UHMWPE liner (X3™), alumina ceramic femoral heads (28, 36 and 44 mm)

4.3 Results Wear of the C-UHMWPE liners (N2Vac) with 28-mm head was the highest of all analysed test specimens (p £ 0.001) after 5 Mio. load cycles; all N2Vac liners showed considerable wear marks at the articulating areas. Wear of X3™ liners in combination with 28-mm alumina ceramic heads was not detectable gravimetrically, though wear marks were found marginally at the end of the tests. Compared to the sequentially X-PE liner (X3™) with 28-mm inner diameter, wear was signiﬁcantly higher at groups with 36 mm (p = 0.004) and 44 mm (p £ 0.001) head sizes. Up to 2.5 Mio. load cycles wear was similar for both X3™ liners with 36 and 44 mm. However, the wear rate increased for the liners with 44 mm during the following 2.5 Mio. load cycles resulting in slightly higher wear after 5 Mio. load cycles compared to the 36 mm (p = 0.07). Both sizes showed marginal wear marks at the liners at the end of the study. The data of the detected wear of the investigated test specimens is shown in Fig. 4.2. The average gravimetrical wear rates of the C-UHMWPE (N2Vac) liners combined with 28-mm alumina ceramic heads amounted to 12.6 ± 0.8 mg/ million cycles. The average gravimetrical wear rates of the X3™ liners in combination with 36- and 44-mm alumina ceramic heads only amounted to 2.0 ± 0.5 mg/million cycles and 3.1 ± 0.3 mg/million cycles, respectively.

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N2Vac-Al2O3, 28 mm X3-AI2O3, 28 mm X3-AI2O3, 36 mm X3-AI2O3, 44 mm

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Wear [mg]

50

x

x

x x x x

40 x 30

x

20

x x

10 0 −10 0

0.5

1.0

1.5

2.0 2.5 3.0 Cycles [Mio.]

3.5

4.0

4.5

5.0

Fig. 4.2 The average gravimetric wear of conventional UHMWPE acetabular liner (N2Vac) combined with 28 mm and sequentially cross-linked PE liner (X3™) combined with 28, 36 and 44 mm out of alumina ceramic femoral heads after 5 million cycles of gait simulation

4.4 Discussion The reduction of wear with X-PE has been determined in several simulator studies [1, 16, 20]. These encouraging results could lead to a lower risk of aseptic loosening and longer life expectancies of THR. First clinical outcome studies with X-PE showed promising results [13, 21, 28, 37] including the investigated sequentially cross-linked polyethylene X3™ [7]. The advantages of larger femoral heads are known [6, 12]; however, most clinical studies describe 28-mm femoral heads combined with X-PE. While another simulator study determined no increased wear of X-PE with larger femoral heads [34], our present study showed an increase of wear with larger heads despite sequential cross-linking of the polyethylene. Indeed 36- and 44-mm heads generate signiﬁcantly lower wear using sequentially X-PE liners compared to the C-UHMWPE liners with 28-mm heads, but the wear was signiﬁcantly higher than in case of 28-mm alumina heads combined with sequential X-PE. Hence, an increase of wear with larger heads was observed despite cross-linking, though wear rates are by far lower than those of C-UHMWPE. These results are also conﬁrmed clinically [24, 29, 30, 38]. Beside the advantages of wear reduction, clinical failures of X-PE acetabular liners have been reported [14, 19, 33, 39, 40]. All of them were caused by unfavourable implant position which resulted mainly in rim fracture of the acetabular liner. Thin X-PE liner wall

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thickness and use of large femoral heads could facilitate these failures. Furthermore, cross-linking the polyethylene, in order to obtain lower wear rates, compromises the mechanical properties, such as ductility and fracture toughness [3, 4, 10, 22]. Therefore, the implant position and implant design as well as adequate wall thickness of X-PE acetabular liners have to be considered carefully, especially for very thin-walled liners such as used within this study, i.e. a wall thickness of only 3.8 mm. The advantages of large femoral heads should not be comprised with reduced mechanical safety of the polyethylene liner. Indeed, the simulator studies showed decreased wear rates for X-PE in standard wear tests, but these tests are limited to reproduce the in vivo situation and do not consider the reasons for the above-mentioned failures. Different aggressive (worst case) wear tests have been performed with X-PE. For instance, X-PE showed decreased wear rates in combination with scratched femoral heads [1] and third-body wear particles [5] compared to C-UHMWPE. However, simulator tests under impingement conditions with X-PE [26] revealed higher wear rates as standard wear tests and demonstrated the weakness of X-PE. More such aggressive wear tests should be performed close to the in vivo situation for better understanding of clinical failures in order to improve existing and to develop new polyethylene materials with decreased in vivo wear rate. This could reduce clinical failures in the future. Furthermore, the biological activity of the wear particles from X-PE has to be clariﬁed. Until now, the inﬂammatory response of these particles are not entirely clear. While smaller particles are generated with X-PE compared to UHMWPE, the biological reaction to these particles could be higher [18, 27]. However, this effect could possibly be negligible by the signiﬁcant lower number of released particles [27]. Hence, the number, size and inﬂammatory consequences of the produced particles in this study, i.e. standard N2Vac polyethylene and X3™ particles, should be investigated in further studies.

4.5 Conclusion The purpose of this experimental study was to evaluate the effect of femoral head size for THR on C-UHMWPE and sequentially X-PE liners. The wear simulator tests showed that the wear rate of UHMWPE liner with small heads (28 mm) decreased signiﬁcantly by cross-linking the PE. The amount of wear for X-PE increased slightly with larger head size (i.e. from 36 to 44 mm) despite cross-linking but is still reduced to a fraction of the wear generated by C-UHMWPE with a 28-mm head. Hence, the advantages of larger femoral head diameters can be exploited by the use of sequentially X-PE which showed superior wear behaviour. However, the biological activity of the particles from sequentially X-PE has to be clariﬁed. Moreover, the thin wall thickness of the liner combined with the cross-linked polyethylene should be regarded with caution because of the reduced mechanical properties. The simulator tests cannot reproduce the worst-case situations in vivo completely, and possible fractures of thin liners cannot be ruled out so far.

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References 1. Affatato S, Bersaglia G, Rocchi M, Taddei P, Fagnano C, Toni A (2005) Wear behaviour of cross-linked polyethylene assessed in vitro under severe conditions. Biomaterials 26: 3259–3267 2. Baker DA, Bellare A, Pruitt L (2003) The effects of degree of crosslinking on the fatigue crack initiation and propagation resistance of orthopedic-grade polyethylene. J Biomed Mater Res A 66:146–154 3. Baker DA, Hastings RS, Pruitt L (1999) Study of fatigue resistance of chemical and radiation crosslinked medical grade ultrahigh molecular weight polyethylene. J Biomed Mater Res 46:573–581 4. Bradford L, Baker D, Ries MD, Pruitt LA (2004) Fatigue crack propagation resistance of highly crosslinked polyethylene. Clin Orthop Relat Res 429:68–72 5. Bragdon CR, Jasty M, Muratoglu OK, O’Connor DO, Harris WH (2003) Third-body wear of highly cross-linked polyethylene in a hip simulator. J Arthroplasty 18:553–561 6. Burroughs BR, Hallstrom B, Golladay GJ, Hoeffel D, Harris WH (2005) Range of motion and stability in total hip arthroplasty with 28-, 32-, 38-, and 44-mm femoral head sizes. J Arthroplasty 20:11–19 7. Campbell DG, Field JR, Callary SA (2010) Second-generation highly cross-linked X3 polyethylene wear: a preliminary radiostereometric analysis study. Clin Orthop Relat Res 468:2704–2709 8. Catelas I, Wimmer MA, Utzschneider S (2011) Polyethylene and metal wear particles: characteristics and biological effects. Semin Immunopathol 33:257–271 9. Clohisy JC, Calvert G, Tull F, McDonald D, Maloney WJ (2004) Reasons for revision hip surgery: a retrospective review. Clin Orthop Relat Res 429:188–192 10. Cole JC, Lemons JE, Eberhardt AW (2002) Gamma irradiation alters fatigue-crack behavior and fracture toughness in 1900H and GUR 1050 UHMWPE. J Biomed Mater Res 63: 559–566 11. Collier JP, Currier BH, Kennedy FE, Currier JH, Timmins GS, Jackson SK et al (2003) Comparison of cross-linked polyethylene materials for orthopaedic applications. Clin Orthop Relat Res 414:289–304 12. Crowninshield RD, Maloney WJ, Wentz DH, Humphrey SM, Blanchard CR (2004) Biomechanics of large femoral heads: what they do and don’t do. Clin Orthop Relat Res 429:102–107 13. Digas G, Karrholm J, Thanner J, Herberts P (2007) 5-year experience of highly cross-linked polyethylene in cemented and uncemented sockets: two randomized studies using radiostereometric analysis. Acta Orthop 78:746–754 14. Duffy GP, Wannomae KK, Rowell SL, Muratoglu OK (2009) Fracture of a cross-linked polyethylene liner due to impingement. J Arthroplasty 24:158–159 15. Dumbleton JH, Manley MT, Edidin AA (2002) A literature review of the association between wear rate and osteolysis in total hip arthroplasty. J Arthroplasty 17:649–661 16. Endo M, Tipper JL, Barton DC, Stone MH, Ingham E, Fisher J (2002) Comparison of wear, wear debris and functional biological activity of moderately crosslinked and non-crosslinked polyethylenes in hip prostheses. Proc Inst Mech Eng H 216:111–122 17. Essner A, Schmidig G, Herrera L, Yau SS, Wang A, Dumbleton JH et al (2005) Hip wear performance of a next generation cross-linked and annealed polyethylene. Poster no. 0830, 51st annual meeting of the Orthopaedic Research Society, Washington DC 18. Fisher J, McEwen HM, Tipper JL, Galvin AL, Ingram J, Kamali A et al (2004) Wear, debris, and biologic activity of cross-linked polyethylene in the knee: beneﬁts and potential concerns. Clin Orthop Relat Res 428:114–119 19. Furmanski J, Anderson M, Bal S, Greenwald AS, Halley D, Penenberg B et al (2009) Clinical fracture of cross-linked UHMWPE acetabular liners. Biomaterials 30:5572–5582 20. Geerdink CH, Grimm B, Ramakrishnan R, Rondhuis J, Verburg AJ, Tonino AJ (2006) Crosslinked polyethylene compared to conventional polyethylene in total hip replacement: pre-clinical evaluation, in-vitro testing and prospective clinical follow-up study. Acta Orthop 77:719–725

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21. Geerdink CH, Grimm B, Vencken W, Heyligers IC, Tonino AJ (2009) Cross-linked compared with historical polyethylene in THA: an 8-year clinical study. Clin Orthop Relat Res 467: 979–984 22. Gencur SJ, Rimnac CM, Kurtz SM (2006) Fatigue crack propagation resistance of virgin and highly crosslinked, thermally treated ultra-high molecular weight polyethylene. Biomaterials 27:1550–1557 23. Gibon E, Ma T, Ren PG, Fritton K, Biswal S, Yao Z et al (2011) Selective inhibition of the MCP-1-CCR2 ligand-receptor axis decreases systemic trafﬁcking of macrophages in the presence of UHMWPE particles. J Orthop Res. doi:10.1002/jor.21548 24. Hammerberg EM, Wan Z, Dastane M, Dorr LD (2010) Wear and range of motion of different femoral head sizes. J Arthroplasty 25:839–843 25. Harris WH (2001) Wear and periprosthetic osteolysis: the problem. Clin Orthop Relat Res 393:66–70 26. Holley KG, Furman BD, Babalola OM, Lipman JD, Padgett DE, Wright TM (2005) Impingement of acetabular cups in a hip simulator: comparison of highly cross-linked and conventional polyethylene. J Arthroplasty 20:77–86 27. Illgen RL, Forsythe TM, Pike JW, Laurent MP, Blanchard CR (2008) Highly crosslinked vs conventional polyethylene particles – an in vitro comparison of biologic activities. J Arthroplasty 23:721–731 28. Knahr K, Pospischill M, Kottig P, Schneider W, Plenk H Jr (2007) Retrieval analyses of highly cross-linked polyethylene acetabular liners four and ﬁve years after implantation. J Bone Joint Surg Br 89:1036–1041 29. Lachiewicz PF, Heckman DS, Soileau ES, Mangla J, Martell JM (2009) Femoral head size and wear of highly cross-linked polyethylene at 5 to 8 years. Clin Orthop Relat Res 467: 3290–3296 30. Livermore J, Ilstrup D, Morrey B (1990) Effect of femoral head size on wear of the polyethylene acetabular component. J Bone Joint Surg Am 72:518–528 31. Maloney WJ (2003) Orthopaedic crossﬁre – larger femoral heads: a triumph of hope over reason! In opposition. J Arthroplasty 18:85–87 32. Markel DC, Mendelson SD, Yudelev M, Essner A, Yau SS, Wang A (2008) The effect of neutron radiation on conventional and highly cross-linked ultrahigh-molecular-weight polyethylene wear. J Arthroplasty 23:732–735 33. Moore KD, Beck PR, Petersen DW, Cuckler JM, Lemons JE, Eberhardt AW (2008) Early failure of a cross-linked polyethylene acetabular liner. A case report. J Bone Joint Surg Am 90:2499–2504 34. Muratoglu OK, Bragdon CR, O’Connor D, Perinchief RS, Estok DM, Jasty M et al (2001) Larger diameter femoral heads used in conjunction with a highly cross-linked ultra-high molecular weight polyethylene: a new concept. J Arthroplasty 16:24–30 35. Orradre BI, Romero R, Brun M, Lopez Blasco JJ (2011) Cross-linked ultra-high-molecular weight polyethylene liner and ceramic femoral head in total hip arthroplasty: a prospective study at 5 years follow-up. Arch Orthop Trauma Surg 131:1711–1716 36. Ries MD, Pruitt L (2005) Effect of cross-linking on the microstructure and mechanical properties of ultra-high molecular weight polyethylene. Clin Orthop Relat Res 440:149–156 37. Shia DS, Clohisy JC, Schinsky MF, Martell JM, Maloney WJ (2009) THA with highly crosslinked polyethylene in patients 50 years or younger. Clin Orthop Relat Res 467:2059–2065 38. Tarasevicius S, Robertsson O, Kesteris U, Kalesinskas RJ, Wingstrand H (2008) Effect of femoral head size on polyethylene wear and synovitis after total hip arthroplasty: a sonographic and radiographic study of 39 patients. Acta Orthop 79:489–493 39. Tower SS, Currier JH, Currier BH, Lyford KA, Van Citters DW, Mayor MB (2007) Rim cracking of the cross-linked longevity polyethylene acetabular liner after total hip arthroplasty. J Bone Joint Surg Am 89:2212–2217 40. Waewsawangwong W, Goodman SB (2012) Unexpected failure of highly cross-linked polyethylene acetabular liner. J Arthroplasty 27:323e1–323e4

Characterisation of Vitamin E–Blended UHMWPE for Higher In Vivo Performance in Orthopaedic Arthroplasty

5

Luigi Costa, Marco Regis, Pierangiola Bracco, Luca Giorgini, and Simonetta Fusi

5.1 Introduction Wear is one of the most limiting factors for the UHMWPE use in orthopaedic implants [19]. The development of a new generation of UHMWPEs has therefore to overcome this problem: reducing wear particle generation that causes osteolysis. It was found that g-irradiation (initially introduced as a sterilisation practice) enhanced the UHMWPE wear resistance but introduced chain scission and subsequent oxidation [7, 14, 15, 26]. In order to eliminate the problem, post-irradiation heat treatments were introduced, like annealing or remelting, that allowed the residual free radicals to recombine [5, 24] but at the same time lowered signiﬁcantly the mechanical properties of the polymer, especially fatigue strength [17]. Thus, the ﬁndings so far were not able to enhance the UHMWPE wear resistance without decreasing other essential properties for its duration in orthopaedic purposes. The state of the art is a cross-linked UHMWPE, irradiated and subsequently annealed/remelted.

L. Costa (*) • P. Bracco IFM Chemistry Department, Torino University, Via P. Giuria 7, 10125 Torino, Italy e-mail: [email protected] M. Regis • S. Fusi R&D Department, LimaCorporate SpA, Via Nazionale 52, 33038 Villanova di San Daniele, Udine, Italy L. Giorgini Hip Division, LimaCorporate SpA, Via Nazionale 52, 33038 Villanova di San Daniele, Udine, Italy K. Knahr (ed.), Total Hip Arthroplasty, DOI 10.1007/978-3-642-27361-2_5, © 2012 EFORT

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Moreover, recent studies demonstrated how in vivo mechanical stress and oxidation are correlated [34] and highlighted the need to ﬁnd a solution to protect the UHMWPE from in vivo oxidation phenomena. The future development of the material has therefore to be found in stabilising and preventing the oxidation occurrence. Recently, a method to develop an oxidation-resistant UHMWPE was the additivation with vitamin E (a-tocopherol). The role of the additive is to react with free radicals in the UHMWPE, preventing them to combinate with oxygen thus avoiding chain scission reactions and the subsequent UHMWPE degradation [9, 12, 13, 30]. There are two methods for incorporating vitamin E in the UHMWPE. One is blending vitamin E with UHMWPE powder before consolidation, while the other is diffusing vitamin E into UHMWPE [27, 28, 31]. The ﬁrst method leads to a better vitamin E distribution inside the polymer but decreases the cross-linking efﬁciency by the reaction between vitamin E and the newly formed macroradicals [29, 32, 33]. Therefore, the vitamin E concentration and the radiation dose have to be optimised in order to create a cross-linked and oxidation-resistant UHMWPE. The vitamin E diffusion into the polymer after irradiation instead does not inﬂuence the crosslinking efﬁciency, since vitamin E is not present during irradiation, but let the material remain unprotected from g-rays, and a homogenesation step is required to uniform as much as possible the vitamin E concentration throughout the material [8, 30]. This said, the international standards regulating the use of UHMWPE in orthopaedic applications do not foresee the use of additives, although at the same time, there is a standard providing indications for a blended UHMWPE [3, 4]. Further, several studies indicate alternative additivations as an optimal solution for enhancing UHMWPE properties. Among all these possibilities and prescriptions, there is the need of a better understanding of which is the best additivation choice, and particularly vitamin E additivation, despite being promising, has to be accurately veriﬁed since the role of a-tocopherol in the interaction with human tissues and its effect on the mechanical and tribological properties has to be fully understood yet [25]. The aim of this study is to fully characterise a possible additivation solution, an irradiated vitamin E–blended UHMWPE, and to compare the results of the characterisation with the correspondent results on a state-of-the-art non-additivated irradiated and remelted UHMWPE.

5.2 Materials and Methods The samples at our disposal were taken from a UHMWPE sheet (1,000 × 500 × 60 mm) produced from blended GUR 1020 resin and 98.6% pure a-tocopherol by Orthoplastics (Bacup, UK). The total amount of blended vitamin E was 0.1% wt. The material was cut in 60 × 60 × 40-mm blocks and then b-irradiated (75 kGy) to induce cross-linking of the polymer chains. The reference material was a GUR 1050, irradiated and remelted standard UHMWPE (UHMWPE X-Lima, LimaCorporate, Villanova di S. Daniele, Italy) of the same shape and size. The irradiation process for the two different materials was the same as well. Specimens were machined in the desired shape by LimaCorporate. A full list of the samples used is illustrated in Table 5.1.

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Table 5.1 Sample at disposal for this study Sample 60 × 60 × 40 mm block

n 1

Material GUR 1050 UHMWPE irradiated and remelted

Test DSC

60 × 60 × 40 mm block

1

DSC

60 × 60 × 40 mm block 60 × 60 × 40 mm block

1

60 × 60 × 40 mm block 60 × 60 × 40 mm block

1

60 × 60 × 40 mm block 60 × 60 × 40 mm block

5

60 × 60 × 40 mm block

8

60 × 60 × 40 mm block

1

Acetabular liner

6

Acetabular liner

6

GUR 1020 UHMWPE + vitamin E irradiated GUR 1050 UHMWPE irradiated and remelted GUR 1020 UHMWPE + vitamin E irradiated GUR 1050 UHMWPE irradiated and remelted GUR 1020 UHMWPE + vitamin E irradiated GUR 1050 UHMWPE irradiated and remelted GUR 1020 UHMWPE + vitamin E irradiated GUR 1020 UHMWPE + vitamin E irradiated GUR 1020 UHMWPE + vitamin E irradiated GUR 1050 UHMWPE irradiated and remelted GUR 1020 UHMWPE + vitamin E irradiated

1

1

5

Area Chemicophysicomechanical characterisation

FTIR FTIR

Oxidative stability Oxidative stability

Tensile test Tensile test

In vitro tests

Biocompatibility evaluation

In vivo tests

Wear simulation

Tribological assessment

Wear simulation

Tests performed regarded both mechanical-tribological properties and interaction with cells, thus biocompatibility. As it can be seen from Table 5.1, tests can be divided in three groups: chemico-physico-mechanical characterisation, biocompatibility and wear assessment.

5.2.1 Chemico-Physico-Mechanical Characterisation DSC measurements have been conducted to evaluate the crystallinity of the samples by using a Perkin-Elmer DSC6 differential scanning calorimeter. The test was carried out heating the samples from 30°C to 200°C at 10°/min and cooling down to 30°C at the same rate. The passages were repeated twice in order to clear the thermal history of the material and determine the percentage of the crystalline phase. During heating, an inert nitrogen

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ambient was maintained. Crystallinity percentage was calculated after the second heating by the ratio between the DH measured value and the DH standard value (293 J/g) [6, 18]. A Reicher-Jung POLYCUT S microtome was used (cutting speed 4 cm/s) to obtain thin slices (~150-mm thickness) from the blocks for FTIR analysis. FTIR spectroscopy was performed to determine the vitamin E percentage throughout the specimen’s thickness and to evaluate the oxidation level of the samples before and after the oxidative stability test. Spottedand line-scan measurements (transmission mode, 16 scans at 4 cm−1 resolution for each point, auto-focus every tenth scan, 1 scan every 100 mm) were collected using a Perkin-Elmer SPECTRUM SPOTLIGHT 300 auto-image microscope. The spot dimension of the FTIR aperture was 100 × 100 mm. All spectra were normalised at 2,020 cm−1, and all the wavelengths of the main oxidation products absorptions were investigated [11], as well as the peak values typical of vitamin E and trans-vinylene [10], to determine the amount of additive and the double bond presence due to the irradiation treatment on cross-linked samples. FTIR measurements have been repeated before and after the oxidative stability test, carried out on the thin slices in a ventilated even at 90˚C [9]. The mechanical characterisation consisted in the preparation of dog-bone specimens for tensile testing and elastic modulus determination from the UHMWPE blocks by machining operations. Tests were carried out following ISO 527 and ASTM D638 (ASTM [2, 21]). The number of samples was ten for each material.

5.2.2 Biocompatibility In Vitro and In Vivo Studies The biocompatibility tests were performed only on additivated UHMWPE, following ISO 10993 prescriptions [23]. A full detailed list of tests and conditions is reported in Table 5.2. Specimens were prepared by machining starting from blocks. After machining, samples were cleaned with a multiple-step automatic cleaning system, Pluritank 70 (Novatec, S. Martino di Lupari, Italy) in differentiated passages of ultrasonic washing, rinsing and ﬁnal drying and sterilised (EtO) to remove all the residuals from the sample preparation. The same procedure was followed for every sample. All biocompatibility tests except cytotoxicity have been carried out at MDT laboratories (MDT, Ochsenhausen, Germany). Cytotoxicity was performed in Biolab laboratories (Euroﬁns-Biolab, Vimodrone, Italy). All the biocompatibility tests were made in good laboratory practice (GLP) conditions.

5.2.3 Wear Test The purpose of the wear test was to determine the wear behaviour of the blended UHMWPE in a hip joint made with the Delta system geometry (LimaCorporate, Villanova di S. Daniele, Italy) and compare it with the same test results on the non-additivated material. The selected coupling for the test was Ø36 mm liners vs. Ø36 mm CoCrMo femoral heads

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Table 5.2 Biocompatibility tests and specimens Specimens Ø20 mm h1,5-mm disks

n 25

Ø20 mm h1,5-mm disks

30

Ø20 mm h1,5-mm disks

30

Ø20 mm h1,5-mm disks

30

Ø20 mm h1,5-mm disks

30

Ø3 mm h10 mm cylinders

15

Material GUR 1020 UHMWPE + vitamin E irradiated GUR 1020 UHMWPE + vitamin E irradiated GUR 1020 UHMWPE + vitamin E irradiated GUR 1020 UHMWPE + vitamin E irradiated GUR 1020 UHMWPE + vitamin E irradiated GUR 1020 UHMWPE + vitamin E irradiated

Test Cytotoxicity

ISO ref. 10993-5

Genotoxicity

10993-3

Intra-cutaneous reactivity

10993-10

Acute systemic toxicity

10993-11

Maximisation

10993-10

Implant

10993-6

for the vitamin E–blended UHMWPE and Ø28 mm liners vs. Ø28 mm CoCrMo femoral heads for non-additivated material. Since it has been demonstrated that higher wear occurs for larger diameter bearings [20], this test has evaluated a worst-case scenario for the vitamin E–blended UHMWPE, comparing the results to a standard coupling of the reference material. Wear tests have been carried out following the ISO 14242 standard [22] by using a servo hydraulic six-station hip simulator (EndoLab, Rosenheim, Germany). Test parameters were set accordingly to the ISO standard, and the liners were oriented in the correct anatomic position so as to apply the resulting hip joint load directly to the liner-cup system. In this way, the force vector was constant with respect to the cup and varied with respect to the head. EDTA has been added to the serum to bind the calcium, and patricin (50 mg/l) has been added to retard bacteria-induced degradation. The composition of the serum was therefore the following: 18.82 g/l protein content, 1.86 g/l EDTA content and 10.0 ml/l patricin. Cleaning procedure before weight measurements was done by alternate steps of rinsing in deionised water, vibrating 10 min in deionised water and ultrasonic cleaning agent, with a ﬁnal 5-min soak in isopropanol and drying in a vacuum chamber (0.133 mbar) for 30 min. All mass measurements have been made using a high-precision balance (Sartorius CP225D). Specimens have been removed from the hip simulator station at 500 000 cycle one million cycles and one million cycles intervals thereafter to determine the mass loss and to evaluate the contact area optically. Serum has been replaced every 500 k cycles. The specimens have been changed periodically between different stations. At the end of the test, optical microscope images of the liners bearing surfaces were taken to evaluate the bearing surface morphology of the material after ﬁve million cycles in different areas. A map of the liner areas investigated with the microscope is reported in Fig. 5.1.

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Fig. 5.1 Positions of areas investigated by optical microscope after the wear test on the liner bearing surface (left) and on the femoral head bearing surface (right)

Superior

Superior

E

E A

A Anterior

B

D

C

Cu p

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B Anterior

D

all

B C

5.3 Results 5.3.1 Chemico-Physico-Mechanical Properties The results of DSC measurements are 46 ± 2% and 45 ± 2% for the non-additivated and the vitamin E–blended UHMWPEs, respectively. Crystallinity percentage for the two different materials is thus similar, also considering that the percentage error of the tests is 2%. FTIR results on the microtomed samples performed before the accelerated ageing test reported that non-additivated material, as well as vitamin E–blended UHMWPE, have negligible oxidation values throughout their entire cross section (Fig. 5.2). FTIR measurements indicate that no oxidation product presence could be retrieved in the line-scan spectra, showing that the external surface, as well as the bulk material, was not subjected to degradation due to the production process or the machining and sample preparation. It can be noted that, in correspondence of the external edges of the thin ﬁlms at 0 and 30–35,000-mm thickness, a certain presence of esters and ketones was detected. Esters presence is due to the microtome cut of the blocks for the preparation of thin ﬁlm samples necessary for IR analysis, as reported in literature [16], and ketones, due to the external surface oxidation of the blocks caused by the elapsed time between irradiation and post-irradiation remelting. However, the surface oxidation is not considered to be critical because machining operations will remove the oxidised material away from the blocks to obtain the ﬁnal geometry of the desired component. A representative image of the 1,600–2,100 cm−1 region of the IR spectra scanned during the accelerated ageing test, at regular intervals of approximately 50 h, is shown in Fig. 5.3. As said, oxidation level was evaluated not considering esters peak (1,740 cm−1) so as not to introduce measurement deviations by microtoming.

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a 0.15

Absorbance

0.1

0.05 35,000 30,000 25,000 20,000 15,000 Depth 10,000 (microns) 5,000

0

2,100

2,000

1,900

1,800

1,700

1,600

Wavenumber (cm−1)

b 0.15

Absorbance

0.1

0.05 25,000 20,000 15,000 10,000 Depth 5,000 (microns)

0 0 2,100

2,000

1,900

1,800

1,700

1,600

Wavenumber (cm−1)

Fig. 5.2 Line scan of non-additivated UHMWPE (a) and vitamin E–blended UHMWPE (b) samples

It is possible to notice that the amount of oxidation level, in terms of oxidation product peak height, occurs for both non-additivated UHMWPE and vitamin E–blended material, but while the non-additivated irradiated and remelted UHMWPE samples exhibit an oxidation level of 0.1 after 797 h in oxidative ambient, the vitamin E–added UHMWPE, despite the absence of a post-irradiation treatment, begins to get oxidised after 1,893 h, and with minimum oxidation levels, around 0.025, that is two orders of magnitude less than the observed oxidation of the reference material.

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a 0.4

Absorbance

0.3

0.2

0.1

0 2,100

2,000

1,900

1,800

1,700

1,600

Wavenumber (cm−1)

b 0.4

0.3

Absorbance

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0.2

0.1

0

2,100

2,000

1,900 1,800 Wavenumber (cm−1)

1,700

1,600

Fig. 5.3 IR spectra during accelerated ageing test for non-additivated UHMWPE (a) and vitamin E–blended UHMWPE (b)

The trend of the oxidation products quantitative amount, in terms of ketones concentration, conﬁrmed these indications (Fig. 5.4). The oxidation level of the non-additivated material becomes detectable (0.01) after 700 h, and the oxidation products amount rises rapidly, with an exponential trend, while

5

Oxidation trend

0.1 Ketones concentration [mol/l]

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GUR 1050 UHMWPE irradiated+remelted GUR 1020 UHMWPE + Vitamin E irradiated

0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 0

200

400

600

800

1,000 1,200 Time [h]

1,400

1,600

1,800

2,000

Fig. 5.4 Oxidation products quantitative amount for non-additivated and vitamin E–blended UHMWPEs in terms of ketones concentration Vitamin E concentration

Absorbance at 1210 cm−1

0.002 0.00175 0.0015 0.00125 0.001 0.00075 0.0005 0.00025 0 0

5,000

10,000

15,000 20,000 Thickness [micron]

25,000

30,000

Fig. 5.5 Vitamin E presence throughout the sample thickness

the oxidation level of the vitamin E–blended material reaches only a small detectable oxidation level, not comparable to the beginning of the oxidation of non-additivated UHMWPE (0.002), after a considerably higher time (2,000 h), with no sign of an exponential trend of the phenomenon. The vitamin E concentration in the cross section was calculated by examining the peak area at 1,210 cm−1. A concentration proﬁle showing the quantitative amount of the additive throughout the sample thickness was then calculated (Fig. 5.5). Vitamin E concentration was calculated by evaluating the molar concentration and volume. It resulted that the amount of additive was constant across the entire sample thickness, and it was around 0.095% wt, that is in comparable quantities to what was indicated by the supplier.

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Table 5.3 Mechanical characteristics of the tested materials Material GUR 1050 UHMWPE irradiated and remelted GUR 1020 UHMWPE + vitamin E irradiated

Stress [MPa]

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E [GPa] 1.1

sy [MPa] 19

s* [MPa] 33

e [%] 305

1.8

25

43

350

Stress−strain curve

50 45 40 35 30 25 20 15 10 5 0

UHMWPE irradiated+remelted UHMWPE irradiated+vit E 0

50

100

200 150 Strain [%]

250

300

350

Fig. 5.6 Stress–strain curve for non-additivated UHMWPE and vitamin E–blended UHMWPE

Data regarding tensile test are reported in Table 5.3. As it is possible to appreciate, there are some differences between the stress–strain data (Fig. 5.6). This is partly due to the difference in the starting GUR resin, 1050 for the nonadditivated UHMWPE, and 1020 for the vitamin E–blended material, and partly because of the remelting phase performed on the standard UHMWPE to avoid the free radical presence in the material. The elastic moduli were calculated mathematically, following the indications in the reference standards and individuating the slope of the stress–strain curves elastic part. Also for these values, the results were similar between the two UHMWPEs, with some variations due to the starting powders and the presence of a post-irradiation treatment for the non-additivated material.

5.3.2 In Vitro and In Vivo Results The biocompatibility assessment of the vitamin E–blended UHMWPE gave negative results on all the in vitro tests performed. The material was shown to be not cytotoxic and not genotoxic. Further, it did not cause irritation phenomena, and in all implant tests, no adverse events have been reported (Table 5.4). In vitro tests were not affected by deviations; cytotoxicity test showed reactivity grade 0 after 24 h of contact, with a global cell vitality reduction of 12.53%, and genotoxicity test items, whose assays were conducted with and without metabolic activation, did not cause gene mutations by base pair changes or frameshifts in the genome of the tester strain used.

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Table 5.4 Biocompatibility tests and overall results

Test Cytotoxicity Genotoxicity

Record Cell vitality reduction, 12.53% No biologically relevant increases in revertant colony numbers of any of the tested strains observed No signs of irritation; average score for polar and non-polar test item (PII), 0% No signs of toxicity (single exposure to NMRI mice), no compound-related mortalities (within 72 h) Sensitisation rate after application, 0% No compound-related tissue reactions, mortalities or other signs of toxicity

Intracutanous reactivity Acute systemic toxicity Maximisation Implant

Not irritant No acute toxic characteristics No sensitising properties No adverse reactions

Average cumulative wear

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UHMWPE irradiated+remelted ∅28 liner UHMWPE irradiated+vit. E ∅36 liner

45 40 35 Wear [mg]

Results on GUR 1020 UHMWPE + vitamin E irradiated Not cytotoxic Non-mutagenic

30 25 20 15 10 5 0 0

1

2

3 Million cycles

4

5

Fig. 5.7 Wear rate of non-additivated UHMWPE and vitamin E–blended UHMWPE

All the in vivo tests performed resulted in no adverse clinical signs or other adverse changes within the animal groups, as well as no signs of toxicity. In all implant sites, no irritation or other reactions were observed. No weight loss or abnormal food intake were detected, and the body weight development of all the animals was within the expected range.

5.3.3 Wear Assessment Mass loss measurements were corrected with the soaking controls and interpolated to calculate the wear rate between zero and ﬁve million cycles. The overall wear rate is shown in Fig. 5.7. Wear rate of vitamin E–blended UHMWPE is 5.12 mg/million cycle, and the mass loss has no run-in stage. The non-additivated cross-linked UHMWPE instead show a run-in

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Cycles [mio]

Liner coupling

Cycles [mio]

0.5

3.0

1.0

4.0

2.0

5.0

Liner coupling

Fig. 5.8 Vitamin E–blended UHMWPE detected contact areas at every measurement step during wear test

stage within the ﬁrst 0.5 million cycles, and a second wear rate up to ﬁve million cycles. As a result, the overall wear for non-additivated material is slightly higher than the wear of vitamin E–blended UHMWPE (6.13 mg/million cycle), but considering the different wear trend, between the two materials it is expected that after ﬁve million cycles, the overall wear of the additivated material will be higher than the reference UHMPWE. The images of the contact areas of additivated UHMWPE are shown in Fig. 5.8. At every step, no macroscopic wear damages or patterns were visible on the coupling surface of the liners. A further evaluation at the optical microscope of the vitamin E–blended liner bearing surface was performed to ﬁnd any surface damage on the samples (Fig. 5.9). Images show no detectable damages on the femoral heads and regular scratches

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on the polymer liners. No differences in terms of surface appearance were found between additivated and non-additivated material.

5.4 Discussion DSC measurements showed that no signiﬁcant changes in crystallinity are related to the vitamin E blending within the UHMWPE resin. Regarding the chemico-physico-mechanical characterisation, both UHMWPEs show comparable values of mechanical strength and

Fig. 5.9 Optical microscope images of the bearing surface of vitamin E–blended UHMWPE. (a) UHMWPE liners; (b) CoCrMo femoral heads

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5

Fig. 5.9 (continued)

elongation. However, the post-irradiation thermal treatment has shown to be detrimental for the non-additivated UHMWPE characteristics, leading to a lower yield stress and elastic modulus. Therefore, the vitamin E presence, allowing the post-irradiation thermal treatment elimination, leads to the preparation of a cross-linked UHMWPE with better mechanical properties. It is therefore expectable that the in vivo behaviour of the vitamin E–blended material will be signiﬁcantly better in terms of mechanical properties preservation. The post-irradiation treatment elimination is possible thanks to the presence of vitamin E that reacts with the residual macroradicals left by the cross-linking process. Further, the antioxidant presence ensures a considerably higher oxidation resistance of the vitamin E–blended UHMWPE. The macroalkyl reaction with oxygen is hindered by their reaction with vitamin E. In this way, the oxidation product formation is signiﬁcantly lowered, and instead there is the formation of a stable tocopherol radical. As mentioned above, the cutting process for the thin

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ﬁlm samples preparation leads to the polymer chain scissions and the subsequent formation of esters. Therefore, their presence in the sample and the rise of esters amount within the oxidative stability test is considered not to be indicative of a degradation of the material. Consequently, it is possible to conclude that vitamin E–blended UHMWPE is considerably more stable to oxidation phenomena than non-additivated material. Considering that in vivo mechanical stress induces the oxidation of UHMWPE and the following loss of mechanical properties [34], the combined effect of a material with enhanced mechanical properties and enhanced oxidative stability is assumed to improve the in vivo lifetime of the component. In this sense, it is preferable to have a vitamin E–blended UHMWPE instead of a vitamin E–diffused material since the vitamin E concentration in the blended material has shown to be constant and regular throughout the entire material thickness, and in this way, the homogenisation treatment performed to assure the correct level of anti-oxidant in the bulk material after its diffusion could be avoided, leading to the preparation of a material with no loss of mechanical properties due to post-processing thermal treatments. Vitamin E quantity and irradiation dose can be tailored to obtain a correct balance between vitamin E presence and cross-linking efﬁciency. The biocompatibility evaluation showed that the additivated material fulﬁls the requirements prescribed by ISO 10993 standards, demonstrating that the vitamin E–blended UHMWPE is not toxic for cell cultures and can be considered safe and well tolerated in vivo. However, there is the need of a deep understanding of the mechanisms regulating the immunitary response of the human implant site to wear particles containing vitamin E, as well as the biological response in vivo for an extended period of implant under mechanical stress and severe working conditions. Wear results demonstrated that the cumulative mass loss of the vitamin E-blended UHMWPE was lower than the correspondent global wear of non-additivated UHMWPE. However, the observed trend after run-in period seems to foresee an inverted result for wear tests at more than ﬁve million cycles. This can be due to the different GUR resin type of the two materials, 1050 for the non-additivated UHMWPE and 1020 for the vitamin E–blended polymer: being the GUR 1050 resin more resistant to wear, it is expectable that wear rate of GUR 1050 will be lower than the GUR 1020 one. The different liner coupling inﬂuenced the test result as well since it was more severe for the additivated UHMWPE. Therefore, it is possible to conclude that vitamin E–blended UHMWPE has equal or better wear resistance than the non-additivated UHMWPE.

5.5 Conclusion The test campaign here conducted was designed to verify the beneﬁts of the UHMWPE additivated with vitamin E use, in respect to mechanical properties, chemical stability, interaction with a biological ambient and tribological properties. The results achieved so far demonstrated that the additivated material retains the beneﬁts of the cross-linking without losing in mechanical properties with post-irradiation treatments. Further, in respect to the non-additivated UHMWPE, it has an extremely higher oxidative stability and an overall wear rate equal or lower.

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Since no changes in biocompatibility tests performed so far can be traced back to the vitamin E additivation, it can therefore be concluded that the choice of a vitamin E–blended UHMWPE has demonstrated to be a potential advantage for orthopaedics and that vitamin E–blended UHMWPE can lead to a lower damage induced by in vivo mechanical stress oxidation and to a better in vivo behaviour of the artiﬁcial joint.

References 1. ASTM International (2002) ASTM F2003–02. Standard practice for accelerated aging of ultra-high molecular weight polyethylene after gamma irradiation in air. West Conshohocken 2. ASTM International (2010) ASTM D638–10. Standard test method for tensile properties of plastics. West Conshohocken 3. ASTM International (2007) ASTM F648–07. Standard speciﬁcation for ultra-high-molecularweight polyethylene powder and fabricated form for surgical implants. West Conshohocken 4. ASTM International (2007) ASTM F2695–07. Standard speciﬁcation for ultra-high molecular weight polyethylene powder blended with alpha-Tocopherol (Vitamin E) and fabricated forms for surgical implant applications. West Conshohocken 5. Bhateja S, Duerst R, Aus E et al (1995) Free radicals trapped in polyethylene crystals. J Macromol Sci Phys B34:263–272 6. Blundell DJ, Beckett DH, Wilcocks PH (1981) Routine crystallinity measurements of polymers by DSC. Polymer 22:704–711 7. Blunn G, Brach del Prever EM, Costa L et al (2002) Ultra high molecular-weight polyethylene (UHMWPE) in joint replacement: fabrication, sterilisation and wear. J Bone Joint Surg Br 84:946–949 8. Bracco P, Oral E (2011) Vitamin E-stabilized UHMWPE for total joint implants. Clin Orthop Relat Res 469:2286–2293 9. Bracco P, Brunella V, Zanetti M et al (2007) Stabilisation of UHMWPE with vitamin E. Polym Degrad Stab 92:2155–2162 10. Costa L, Bracco P (2009) Mechanisms of crosslinking, oxidative degradation and stabilization of UHMWPE. In: Kurtz SM (ed) The UHMWPE biomaterials handbook, 2nd edn. Elsevier Academic Press, Amsterdam 11. Costa L, Brach del Prever EM (2000) UMWPE for arthroplasty. Minerva Medica, Torino 12. Costa L, Luda MP, Trossarelli L (1997) Ultra-high molecular weight polyethylene. I. Mechanooxidative degradation. Polym Degrad Stab 55:329–338 13. Costa L, Luda MP, Trossarelli L (1997) Ultra-high molecular weight polyethylene. II. Thermal- and photo-oxidation. Polym Degrad Stab 58:41–54 14. Costa L, Luda MP, Trossarelli L et al (1998) Oxidation in orthopaedic UHMWPE sterilized by gamma radiation and ethylene oxide. Biomaterials 19:659–668 15. Costa L, Luda MP, Trossarelli L et al (1998) In vivo UHMWPE biodegradation of retrieved prosthesis. Biomaterials 19:1371–1385 16. Costa L, Jacobson K, Bracco P et al (2002) Oxidation of orthopaedic UHMWPE. Biomaterials 23:1613–1624 17. Gencur SJ, Rimnac CM, Kurtz SM (2006) Fatigue crack propagation resistance of virgin and highly crosslinked thermally treated UHMWPE. Biomaterials 27:1550–1557 18. Gray P (1970) Polymer crystallinity determination by DSC. Thermochimica Acta 1:563–577 19. Harris W (1995) The problem is osteolysis. Clin Orthop Relat Res 311:46–53

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20. Hermida JC, Bergula A, Chen P et al (2003) Comparison of the wear rates of twenty-eight and thirty-two-millimeter femoral heads on cross-linked polyethylene acetabular cups in a wear simulator. J Bone Joint Surg Am 85:2325–2331 21. International Organisation for Standardisation (1997) UNI EN ISO 527–2. Determination of tensile properties test conditions for moulding and extrusion plastics. Geneva 22. International Organisation for Standardisation (2002) ISO 14242. Implants for surgery – wear of total hip-joint prostheses. Geneva 23. International Organisation for Standardisation (2009) ISO 10993. Biological evaluation of medical devices. Geneva 24. Keller A, Ungar G (1983) Radiation effects and crystallinity in polyethylene. J Phys Chem 22:155–181 25. Marshall A (2011) Effect of UHMWPE particles on mesenchymal stem cell replication. In: Proceedings of 5th UHMWPE international meeting, Philadelphia, 22–23 Sept 2011 26. McKellop H, Shen FW, Lu B et al (2000) Effect of sterilization method and other modiﬁcations on the wear resistance of acetabular cups made of ultra-high molecular weight polyethylene: a hip simulator study. J Bone Joint Surg Am 82:1708–1725 27. Oral E, Wannomae KK, Hawkins NE et al (2004) a-Tocopherol doped irradiated UHMWPE for high fatigue resistance and low wear. Biomaterials 25:5515–5522 28. Oral E, Greenbaum ES, Malhi AS et al (2005) Characterization of irradiated blends of alphatocopherol and UHMWPE. Biomaterials 26:6657–6663 29. Oral E, Christensen S, Malhi A et al (2006) Wear resistance and mechanical properties of highly crosslinked UHMWPE doped with vitamin E. J Arthroplasty 21:580–591 30. Oral E, Rowell SL, Muratoglu OK (2006) The effect of a-tocopherol on the oxidation and free radical decay in irradiated UHMWPE. Biomaterials 27:5580–5587 31. Oral E, Wannomae KK, Rowell SL et al (2007) Diffusion of vitamin E in ultra-high molecular weight polyethylene. Biomaterials 28:5225–5237 32. Oral E, Godesky Beckos C, Malhi A et al (2008) The effects of high dose irradiation on the cross-linking of vitamin E-blended UHMWPE. Biomaterials 29:3557–3560 33. Parth M, Aust N, Lederer K (2002) Studies on the effect of electron beam irradiation on the molecular structure of ultra-high molecular weight polyethylene under the inﬂuence of alphatocopherol with respect to its application in medical implants. J Mater Sci Mater Med 13:917–921 34. Regis M, Bracco P, Giorgini L et al (2012) J Biomed Mater Res B: Appl Biomat (in press)

Long-Term Reduction of Wear and Osteolysis with Cross-Linked PE? 13-Year Follow-up of a Prospectively Randomized Comparison with Conventional PE

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Bernd Grimm, Alphons Tonino, and Ide Christiaan Heyligers

6.1 Introduction Ultra-high-molecular-weight polyethylene (UHMWPE) has remained the most popular acetabular bearing choice in total hip arthroplasty for many decades despite advances in alternative bearing materials such as ceramic-on-ceramic or metal-on-metal. In combination with a metal or ceramic femoral head, polyethylene offers a low friction and low wear bearing choice with more surgical options than any alternative bearing. Variants are available as all-polyethylene cups or as inserts for metal backed cups, ﬁxation can be cemented or uncemented, hooded cups or inserts are offered to counter luxation, and the maximum range of head diameters from 22 to >40 mm are at the surgeon’s disposal. Polyethylene cups are also considered more forgiving both in surgical handling (e.g., scratching, third particle ingress), acetabular placement (inclination and anteversion), or surgical technique in general (e.g., soft tissue handling). At the same time, polyethylene avoids the problems reported for alternative bearings such as fracture or squeaking (ceramic) and metal ion release or pseudotumors (metal). Some authors also claim biomechanical beneﬁts from the soft polyethylene bearing suspending shocks and transmitting more physiological loads into the periprosthetic bone than the hard-on-hard bearing materials [19]. Polyethylene also presents the lowest cost bearing option. Despite these compelling advantages, polyethylene bearings produce signiﬁcant wear volumes which can limit the lifetime of the hip replacement, requiring revision either by wearing through the bearing or by wear particle–induced osteolysis, leading to aseptic loosening of the cup or the stem. Polyethylene rim fractures of inserts in metal-backed

B. Grimm () • A. Tonino • I.C. Heyligers Department of Orthopaedic Surgery & Traumatology, Atrium Medical Center, AHORSE Research Foundation, Henri Dunant-Str. 5, 6419PC Heerlen, The Netherlands e-mail: [email protected] K. Knahr (ed.), Total Hip Arthroplasty, DOI 10.1007/978-3-642-27361-2_6, © 2012 EFORT

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cups have also been reported as a failure mode but are relatively rare and mostly linked to neck impingement indicating cup malpositioning [11], possibly accelerated by oxidation and suboptimal design of the locking mechanism [10]. However, wear particle–induced osteolysis has been the number one failure mode causing revision surgery hip replacements with polyethylene [16, 23]. The occurrence of osteolysis has been linked to the amount of wear particles released into the tissue so that the concept of a wear threshold has been discussed with wear rates above which osteolysis will inevitably occur or below which the body can tolerate the particles without developing osteolysis [3, 6]. For linear head penetration, a wear volume–related parameter measurable on conventional radiographs, the safe threshold below which authors report permanent absence of osteolysis, is an annual wear rate of 0.05 [1] to 0.1 mm/year [5] for the common 28-mm diameter head. The prevalence of osteolysis is reported to increase proportionally with the wear rate until an upper threshold of 0.4 mm/year head penetration above which osteolysis occurred in all patients [5]. Barrack found this upper threshold to be at 0.2 mm/year [1]. It remains under discussion if a universal threshold truly reﬂects a general dose– response relationship between wear rate and osteolysis because it ignores other effects on the occurrence of osteolysis such as the “pumping effect” of interstitial ﬂuids inﬂuenced by the implant design, ﬁxation, and periprosthetic bone [22]; the presence of cup holes delivering particles directly into the bone [25]; the apparently highly variable individual response with patients tolerating high wear rates; and others developing osteolysis at low rates [6] and the incidence of osteolysis, though rare and less severe, even in bearing materials with very low wear rates and bioinert wear particles such as ceramics [17]. Nevertheless, the wear rate remains the most clearly identiﬁed and strongest factor in the development of osteolysis. Thus, the reduction of the polyethylene wear rate has been the main aim of subsequent generations of new polyethylene variants and the concept of a threshold helps the analysis of clinical wear data in the evaluation of these new variants. Improving the wear resistance of UHMWPE can be achieved by cross-linking, a process on molecular level where free radicals on the molecular chains recombine to link across the same or another molecular strand and thus making the material more wear resistant [18]. The free radicals needed for cross-linking are commonly created by irradiation and maximum cross-link density, and thus, wear resistance can be achieved at a dose near 100 kGy [24]. While the free radicals are required to form cross-links, residual free radicals in the ﬁnal clinical product are not desired because they are highly reactive and cause the polyethylene to oxidize in vivo [18] or even on the shelf when not packed in inert gas but air like the standard polyethylene until the mid-1990s. Oxidation degrades the material so that the wear resistance is harmed or that delamination, cracking, or rim fracture may occur as oxidation is concentrated in the subsurface areas [18]. In order to avoid such oxidation after irradiation cross-linking, the free radicals are being reduced by a heat treatment. Remelting means heating the polyethylene above melt temperature, causing such a high mobility of the molecular chains that free radicals can easily recombine. Thus, cross-linked and remelted PE has a free radical content and thus oxidative potential similar to virgin PE. However, remelting also reduces crystallinity and hence the polyethylene’s strength. Annealing is the alternative heat treatment where polyethylene is heated below melt temperature to maintain crystallinity while still reducing

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free radicals via the increased molecular chain mobility. Less chain mobility than during remelting, albeit maintained for longer periods, results in higher levels of residual free radicals. Thus, its oxidative potential is higher than remelted PE, although the clinical relevance of this measurable difference is yet unknown. The newest generations of polyethylene use alpha-tocopherol (vitamin E) as an antioxidant. Although irradiation has been used for PE sterilization almost since its introduction, the effect on cross-linking and increasing wear resistance has widely been used intentionally since the mid-1990s only. Before, PE received low doses of irradiation for sterilization only, and improvement was made mainly by switching from air to an inert atmosphere (e.g., nitrogen) for packaging to avoid on-the-shelf oxidation. Since the wider introduction of PE intentionally cross-linked for wear reduction, three generations could be distinguished, moderately cross-linked (<50 kGy) PE, highly cross-linked PE (±100 kGy), and highly cross-linked PE which is oxidation stabilized (e.g., by antioxidants or heat treatments). The beneﬁcial effect of cross-linking on reducing wear has been well proven in simulator studies as well as short-term (<5 years) and midterm (5–10 years) clinical studies [2, 20]. However, the main clinical goal of reducing wear, the reduction of osteolysis, has not yet been shown because radiographically visible osteolysis tends to form only during long follow-up. It has also been suggested that wear particles of cross-linked PE are smaller and of a different shape and thus despite lower volumes larger in number and more aggressive so that no reduction in osteolysis may become visible but the opposite [8]. In the case of cross-linked and annealed PE, concerns persist over the residual free radicals oxidizing the material in the long term and thus degrading the wear resistance so that neither a sustained wear reduction nor less osteolysis may become evident in the long term. This study is the longest follow-up of a prospective, randomized clinical comparison between a ﬁrst generation of cross-linked and annealed polyethylene and a then conventional, now historical polyethylene, with a focus on wear and osteolysis. It was the aim of the study to verify if the wear reduction of cross-linked PE can be maintained in the long term or if in vivo oxidative degradation removes or reverses this effect, a concern especially with annealed PE. In addition, radiographic signs of acetabular osteolysis were evaluated to verify if reduced wear results in less osteolysis or if a higher osteolytic potential of the cross-linked wear particles may (over) compensate the beneﬁts of smaller debris volumes.

6.2 Patients and Methods In a prospective study, 48 patients were indicated for primary unilateral total hip arthroplasty (THA) following the diagnosis of osteoarthritis in most cases except 3 patients with posttraumatic arthritis and one with avascular head necrosis. The mean age of the patients (27 female, 21 male) at operation was 63.9 years [48–74 years]. All subjects received the same uncemenented ABG-II implant system (Stryker Orthopaedics, Mahwah, NJ, USA). The system comprises a proximally hydroxyapatite-coated anatomic titanium alloy stem and hydroxyapatite-coated hemispherical acetabular shell made of titanium alloy. All fem-

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Table 6.1 Comparison between the conventional (now historic) PE and Duration PE moderately cross-linked for wear reduction* Conventional PE Duration cross-linked PE Raw material Hoechst GUR 415 Hoechst GUR 415 Irradiation source Co-60 gamma Co-60 gamma Irradiation dose 30 kGy 30 kGy Atmosphere Air Nitrogen Postirradiation treatment None Annealing 50°C/144 h Small punch test* 84.1 N ± 2.2 N 94.3 N ± 3.3 N * p=0.002 (two-tailed student t-test), Load-at-break is a measure of crosslink density

oral heads were of CoCr alloy and measured 28 mm in diameter, thus controlling a major parameter inﬂuencing wear and head penetration. The polyethylene inserts were randomized in triple-blinded fashion to the patient and both the surgeon and observer possibly due to identical visual and radiographic appearance. Patients either received a ﬁrst-generation moderately cross-linked PE (n = 22), DurationTM (Stryker Orthopaedics, Mahwah, NJ, USA), or a then conventional, now “historic” PE (n = 26) which was gamma-irradiated in air for sterilization [14]. Both inserts were manufactured from the same resin (Hoechst GUR 415) and the same ram extrusion process (Poly Hi Solidur, Inc., Reading, PA, USA). The then conventional, now considered historical PE inserts were packaged and sealed in a double-plastic blister surrounded by air, and the package then was gamma-irradiated for sterilization at a dose of 30 kGy. Duration PE, one of the ﬁrst commercially available polyethylene inserts with cross-links introduced and increased intentionally for wear reduction, was produced by placing the machined inserts in two sealed blisters, which were evacuated and then ﬂushed with nitrogen before sealing. The oxygen concentration in the inner blister was less than 0.5% (v/v) and the concentration in the outer blister was less than 5% (v/v) at the time of packaging. The complete package then was gamma-irradiated with a dose of 30 kGy for sterilization and cross-linking. After irradiation, packages were annealed in an oven at a temperature of 50°C for 144 h to further increase cross-link density by promoting free radical recombination (Table 6.1). The elevated cross-link density of the moderately crosslinked PE was veriﬁed using a small punch test [27] showing that the load-at-break, a measure of cross-link density, increased by a similar value (+10.2 N) over the in-air irradiated, nonannealed conventional PE as did this version (+13.4 N) compared to virgin, nonirradiated UHMWPE [12]. Additional mechanical tests showed that strength, stiffness, and elongation to break as a measure of brittleness were hardly affected by the Duration crosslinking process. Patients were assessed using the Harris Hip Score and by taking standing anteroposterior (AP) and lateral (LAT) radiographs for the measurement of wear, implant position and migration, and the assessment of radiographic signs of osteolysis. Time points of assessment were preoperative, at direct post-op (£6 weeks), at 1 year, 2 years, 5 years, 8 years, 10 years postoperatively, and at the ﬁnal follow-up of 12.9 years (12.0–13.3). At this time point, 31 patients (18 conventional, 13 Duration) were left for analysis following eight deaths unrelated to the THA, and nine subjects lost to follow-up mainly due the inability to visit the hospital for a radiograph because of non-THA-related diseases.

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Fig. 6.1 Screenshot of the Roman V 1.70 software being used to measure linear head penetration as polyethylene wear [13, 15]

Wear was measured as linear head penetration [21] on digital AP radiographs (5-MPix resolution) by a single-blinded observer using the Roman V 1.70 software (Institute of Orthopaedics, Oswestry, UK) following a published instruction manual [13, 15] (Fig. 6.1). Accuracy, intraobserver, and interobserver reliability of this software and method are reported to be equal or superior to other common digital methods [13]. Signs of acetabular osteolysis such as formations or radiolucent lines were counted though not rated for size and severity on the AP and LAT radiographs by an experienced, single observer using the DeLee and Charnley zones [4]. The linear wear rates of both groups were compared using a two-tailed student t-test. Proportions of patients with wear rates above or below the clinically relevant thresholds were compared using Fisher’s exact test. Also, the proportions of patients showing radiographic signs of osteolysis were compared using Fisher’s exact test. For the main study hypothesis, the long-term continued reduction in wear rates for cross-linked PE, a priori power analysis (G*Power 3; University of Düsseldorf, Germany), was performed [9] assuming an annual wear rate of 0.15 mm/year for the conventional PE based on literature values [6] and a wear rate of 0.09 mm/year for the Duration PE based on the 45% reduction in linear wear rate predicted from a simulator study [12]. Assuming conservative standard deviations for the wear rate measurement (±0.07 mm/year) based on a pilot study and standard values for alpha (a = 0.05) and power (1 − b = 80%), a total sample size of 46 was calculated for a two-tailed comparison. Due to loss to follow-up at 13 years, post hoc power analysis was performed for the remaining subjects and conﬁrmed a study power of (1 − b) = 86%, beneﬁtting mainly from the lower than assumed standard deviations. Thus despite the loss to follow-up, the study maintained sufﬁcient power.

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6.3 Results Randomization resulted in well-matched groups which were comparable regarding patient characteristics such as age, BMI, and gender ratio; regarding implant parameters such as stem, head, and cup size, as well as cup inclination or liner thickness (Table 6.2). Also, pre-op and post-op Harris Hip Scores were statistically matched, leaving the insert material as the only variable. At 13 years follow-up, the total linear head penetration was signiﬁcantly lower with Duration PE (0.70 mm ±0.36, range: 0.3–1.2 mm) than conventional PE (1.56 mm ±0.83, range: 0.4–3.3 mm, p = 0.015, Table 6.3). Also, the annual wear rate was signiﬁcantly (p = 0.005) lower for Duration (0.063 mm/year ±0.027) than conventional PE (0.122 mm/ year ±0.065). This reduction (−48%) compared well to the original simulator prediction (−45%). The advantage of Duration PE even increased with time as the wear rate reduction grew from −30% at 5 years [12] to −38% at 8 years [14] and from −42% at 10 years to −48% measured in this study at 13 years (Fig. 6.2).

Table 6.2 Comparing patient characteristics and implant parameters between both polyethylene insert groups after randomization Conventional PE Included patients n = 26 Available at last FU n = 18 Age 63.9 years [54–72] Harris Hip Score pre-op 40.2 ± 19.2 Harris Hip Score post-op 92.7 ± 13.5 Stem size 3.7 [2–5] Head diameter 28 mm Cup diameter 53.6 mm [48–62] Cup inclination 46.7° ± 7.3° Liner thickness 8.8 mm [7–11] Groups are statistically matched regarding each parameter

Duration cross-linked PE n = 22 n = 13 63.9 years [48–74] 38.6 ± 16.3 95.1 ± 11.7 3.8 [3–5] 28 mm 53.8 mm [48–60] 48.0° ± 7.3° 8.8 mm [6–12]

Table 6.3 Comparison of total linear head penetration, the annual penetration rate (mean ± SD), and the proportion of subjects with wear rates above the osteolysis threshold Conventional PE Duration`s-linked PE Linear head penetration 1.56 mm ±0.83 0.70 mm ±0.36 Penetration (wear) rate 0.122 mm/year 0.063 mm/year ±0.027 ±0.065 Patients >0.1 mm/year 10/18 = 56% 1/13 = 8% Signs of osteolysis AP 13/18 = 72% 4/13 = 31% Signs of osteolysis LAT 9/18 = 50% 3/13 = 23% AP + LAT combined 22/26 7/26 Patient counts with radiographic signs of osteolysis (e.g., cyst formation)

p-value 0.015 0.005 0.007 0.023 0.099 0.017

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Linear head penetration (wear) during follow-up 2 −48%

Accumulated wear (mm)

1.8 1.6

−42%

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1.2 −30%

1 0.8 0.6 0.4

Conventional PE Duration x-linked, annealed PE

0.2 0 0

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6 8 Follow-up time (years)

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Fig. 6.2 Total linear head penetration (±SD) accumulated for conventional and Duration PE during 13 years of follow-up. The signiﬁcant reduction in wear increases as a percentage advantage Annual wear rate at 13 years 0.3

0.25 Wear rate [mm/yr]

>0.1mm/yr: 56%

>0.1mm/yr: 8%

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Fig. 6.3 Histogram of the individual annual wear rates for conventional and Duration PE at 13 years follow-up with reference to the osteolysis threshold rate of 0.1 mm/year [5]. Patients at risk of developing osteolysis due to high wear rates are signiﬁcantly more frequent in the conventional group, while in the Duration group, most patients are below the threshold

In the Duration PE group, only one patient (1/13 = 8%) had a wear rate above the >0.1 mm/year osteolysis threshold compared to ten (10/18 = 56%) in the conventional PE group (p = 0.007, Fig. 6.3). Patients with radiographic signs of acetabular osteolysis (cysts) on the AP x-ray were less frequent in the Duration (4/13 = 31%) than in conventional group (13/18 = 72%,

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Fig. 6.4 Typical example of a cyst identified on an AP radiograph at 13 years follow-up

p = 0.023). A typical example is represented in Fig. 6.4. This difference became even more pronounced when also the lateral view was evaluated and the affected DeLee-Charnley zones were counted (7 vs. 22, p = 0.017). Only in the conventional group a revision was performed (cup for aseptic loosening). There was no clinical or radiological sign of a rim fracture.

6.4 Discussion With 13 years of follow-up, this study presents results of one of the longest running randomized controlled trials (RCTs) between a conventional, non-cross-linked polyethylene, and cross-linked PE, albeit a ﬁrst generation, moderately cross-linked variant. Long-term (>10 years) clinical trials are less commonly published because of the high effort and cost to monitor patients for such long periods, because the loss to follow-up can easily reach numbers when the study becomes statistically underpowered, and because the questions which were asked at a long gone set-up moment appear to be resolved by short- and midterm clinical studies. However, long-term RCTs are essential to give evidence about in vivo effects which can only be assessed in the long term. The possibility of oxidative degeneration of a cross-linked PE, especially in its annealed variant may be leading to late accelerating wear, the differential development of radiographically visible signs of wear particle–induced osteolysis between cross-linked and non-cross-linked PE, or the concern that wear particles of cross-linked PE are differently shaped, smaller and thus despite smaller wear volumes more numerous and thus of higher osteolytic potential, are all such long-term effects.

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At 13-year follow-up, the total linear head penetration and the annual (wear) rate remained signiﬁcantly lower at almost half the value for Duration PE than for conventional PE. This indicates that even in the long term, moderately cross-linked and annealed PE maintains its wear-reducing properties despite original concerns over oxidative degradation reducing or even reversing the relative wear resistance. Actually, the study showed that the relative advantage of Duration PE increased with time. Thus, oxidative effects on the clinical wear properties can safely be neglected for Duration PE at this follow-up time. The accumulated advantage is so large that even accounting for an unlikely theoretical acceleration of wear beyond 13 years, it probably would last beyond 20 years to equal the total wear of the conventional controls, a time span which exceeds the life expectancy of many THA patients. While this analysis only reﬂects a relative advantage, which may only be of academic but not clinical value, the histogram of wear rate distributions revealed that the beneﬁt of moderate cross-linking is active in a clinically relevant zone. Almost all Duration wear rates were below the osteolysis threshold, while more than half of the patients with conventional PE can be considered at risk. Newer generations of cross-linked PE, the highly cross-linked versions and the highly cross-linked plus oxidation stabilized variants, claim further wear rate reductions totaling >97% against conventional PE based on simulator predictions [7]. With most patients of this study already in the safe zone using a ﬁrst-generation cross-linked PE, it may be that using highly cross-linked PE would not produce signiﬁcantly less osteolysis or revisions in the patients and implants of this study. It appears that highly cross-linked PE variants give a large safety margin which then can be used to expand indication to young and active patients or to facilitate other implant designs such as large-diameter THA or dual-mobility cups. Normally, wear rates are calculated with reference to a baseline at directly post-op or at 1–2 years when PE creep is assumed completed [26]. When the wear rates are calculated not with reference to this baseline but between follow-up points, the relatively superior performance of Duration PE becomes even more pronounced. While the wear rates between subsequent follow-up points (e.g., 8–10 years vs. 10–13 years) are decreasing for both polyethylene variants probably reﬂecting the less active lifestyles of the aging patients, the effect is much stronger for Duration PE. For instance, the mean wear rates for the 8–13 years time period were low in both groups but still >75% lower for Duration (0.02 mm/year) than conventional PE (0.08 mm/year). It is difﬁcult to imagine a mechanism that the Duration PE increases its wear resistance with time. Thus, with well-matched patients and post-op HHS scores suggesting comparable activity levels, the increasing relative advantage may come from a degradation of the conventional PE which does not show as accelerated wear only because it is compensated by the decreasing patient activity. Such degradation by in vivo oxidation can be easily imagined, considering its irradiation sterilization in air and the absence of any postirradiation heat treatment to remove free radicals. If in vivo oxidation would have degraded the wear properties of the conventional PE, then it would be less clear to what degree the advantage of the Duration PE results from the inactivation of free radicals or the increase in cross-link density. Comparing the overall wear reduction of Duration vs. conventional PE at ﬁnal followup (−48%) with original prediction from a hip simulator (−45% at 107 cycles) [12] reveals a compelling similarity between both values well within the standard error of means of

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both measurement methods. However, this match only conﬁrms the predictive quality of relative differences but not of absolute values for wear and or the equivalency of a certain number of simulator cycles with annual steps. This must be investigated in dedicated validation studies. Nevertheless, predictions for the relative wear reduction of newer, highly cross-linked PE variants vs. a control should be trusted with more conﬁdence. The continued development of cross-linked polyethylene variants follows the evidentiary chain that higher cross-link density produces less wear which results in less osteolysis which leads to fewer revisions. Less revisions is the only tangible patient beneﬁt of using these bearings over conventional PE and the only argument toward health-economical justiﬁcation of the more costly materials unless massive wear reductions allow new designs with additional beneﬁts such as luxation prevention. No study so far has proven reduced revision rates with cross-linked over conventional PE partially due to too short follow-up times and partially due to lack of study power. Also, this study cannot give evidence for this. However, acetabular osteolysis, indicating wear particle–induced bone resorption and a risk for future revision, was assessed by counting its incidence, and the occurrence was signiﬁcantly less with Duration than conventional PE. This gives evidence that less wear of Duration PE truly translates into less osteolysis, ﬁnding in line with a recent metaanalysis which pooled 28 studies to derive this conclusion [20]. Less osteolysis with Duration PE also indicates that the wear debris of cross-linked PE may not be of a higher osteolytic potential, at least not for the moderately cross-linked variant in this study or at least not of such an elevated osteolytic potential to compensate for the reduced wear volume. The profound difference in the prevalence of osteolysis (>50% less frequent) in correlation with the reduced wear rates (−48%) seems to supports the concept of an osteolysis threshold for the wear rate. However, the absolute value commonly assumed (0.1 mm/ year) for the complete absence of osteolysis did not apply in this study. One reason may be the variable radiographic assessment of cysts as signs of osteolysis which has a low interrater reliability. Nevertheless, the relative difference identiﬁed by the same observer is reliable. In a future study, cyst formation is to be assessed on 3D CT to also capture oblique cysts and not only count their prevalence but assess severity by measuring their volume. Recently published comparisons between conventional PE (irradiated in inert gas) and highly cross-linked PE (HXLPE) at midterm follow-up (7–10 years) showed wear rate reductions of −86% [26], −78% [2], and −69% [20]. Although direct comparison is difﬁcult due to different study methods (RCT, retrospective matching, meta-analysis), different wear rate calculations, and different HXLPE or control, it is clear that HXLPE produces even higher wear rate reductions than a moderately cross-linked PE. A continuation of this wear reduction in the long term can be expected with more conﬁdence. In conclusion, this study provided evidence that a ﬁrst-generation moderately crosslinked and annealed polyethylene bearing continues to provide signiﬁcantly reduced wear rates and results in signiﬁcantly less osteolytic cyst formation compared to conventional PE at 13 years follow-up. Thus, no clinical evidence of oxidative degradation or elevated osteolytic potential of the wear debris was found for this ﬁrst-generation moderately crosslinked and annealed polyethylene. Changing to cross-linked PE or upgrading to newer generations of highly cross-linked PE does not require a change of surgical technique while promising tangible long-term clinical beneﬁts at comparatively low cost. However, care

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must still be taken when extrapolating these results to the long-term performance of highly cross-linked PE variants, especially when their improved wear performance is used to justify design changes such as increasing head diameters or decreasing insert thickness.

References 1. Barrack RL, Folgueras A, Munn B, Tvetden D, Sharkey P (1997) Pelvic lysis and polyethylene wear at 5–8 years in an uncemented total hip. Clin Orthop Relat Res 335:211–217 2. Capello WN, D’Antonio JA, Ramakrishnan R, Naughton M (2011) Continued improved wear with an annealed highly cross-linked polyethylene. Clin Orthop Relat Res 469(3):825–830. doi:10.1007/s11999-010-1556-5 3. Charnley J, Halley DK (1975) Rate of wear in total hip replacement. Clin Orthop 112:170 4. DeLee JG, Charnley J (1976) Radiological demarcation of cemented sockets in total hip replacement. Clin Orthop Relat Res 121:20–32 5. Dowd JE, Sychterz CJ, Young AM, Engh CA (2000) Characterization of long-term femoralhead-penetration rates. Association with and prediction of osteolysis. J Bone Joint Surg Am 82-A(8):1102–1107 6. Dumbleton JH, Manley MT, Edidin AA (2002) A literature review of the association between wear rate and osteolysis in total hip arthroplasty. J Arthroplasty 17:649–661. doi:10.1054/ arth.2002.33664 7. Dumbleton JH, D’Antonio JA, Manley MT, Capello WN, Wang A (2006) The basis for a second-generation highly cross-linked UHMWPE. Clin Orthop Relat Res 453:265–271. doi:10.1097/01.blo.0000238856.61862.7d 8. Endo M, Tipper JL, Barton DC, Stone MH, Ingham E, Fisher J (2002) Comparison of wear, wear debris and functional biological activity of moderately crosslinked and noncrosslinked polyethylene in hip prostheses. Proc Inst Mech Eng 216 H:111–122. doi:10.1243/0954411021536333 9. Faul F, Erdfelder E, Lang AG, Buchner A (2007) G*Power 3: a ﬂexible statistical power analysis program for the social, behavioral, and biomedical sciences. Behav Res Methods 39(2):175–191. doi:10.3758/BF03193146 10. Furmanski J, Anderson M, Bal S, Greenwald AS, Halley D, Penenberg B, Ries M, Pruitt L (2009) Clinical fracture of cross-linked UHMWPE acetabular liners. Biomaterials 30(29):5572– 5582. doi:10.1016/j.biomaterials.2009.07.013 11. Furmanski J, Kraay MJ, Rimnac CM (2011) Crack initiation in retrieved cross-linked highly cross-linked ultrahigh-molecular-weight polyethylene acetabular liners: an investigation of 9 cases. J Arthroplasty 26(5):796–801. doi:10.1016/j.arth.2010.07.016 12. Geerdink CH, Grimm B, Ramakrishnan R, Rondhuis J, Verburg AJ, Tonino AJ (2006) Crosslinked polyethylene compared to conventional polyethylene in total hip replacement: pre-clinical evaluation, in-vitro testing and prospective clinical follow-up study. Acta Orthop 77(5):719–725. doi:10.1080/17453670610012890 13. Geerdink CH, Grimm B, Vencken W, Heyligers IC, Tonino AJ (2008) The determination of linear and angular penetration of the femoral head into the acetabular component as an assessment of wear in total hip replacement: a comparison of four computer-assisted methods. J Bone Joint Surg Br 90(7):839–846. doi:10.1302/0301-620X.90B7.20305 14. Geerdink CH, Grimm B, Vencken W, Heyligers IC, Tonino AJ (2009) Cross-linked compared with historical polyethylene in THA: an 8-year clinical study. Clin Orthop Relat Res 467(4):979–984. doi:10.1007/s11999-008-0628-2 15. Grimm B (2008) Acetabular PE wear measurement (linear head penetration) using Roman V1.70. http://www.eors.info/Docs/WearRomanManual.pdf. Accessed 7 Nov 2011 16. Harris WH (2001) Wear and periprosthetic osteolysis: the problem. Clin Orthop Relat Res 393:66–70

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17. Hernigou P, Zilber S, Filippini P, Poignard A (2009) Ceramic-ceramic bearing decreases osteolysis: a 20-year study versus ceramic-polyethylene on the contralateral hip. Clin Orthop Relat Res 467(9):2274–2280. doi:10.1007/s11999-009-0773-2 18. Kurtz SM (2009) UHMWPE biomaterials handbook – ultra-high molecular weight polyethylene in total joint replacement and medical devices, 2nd edn. Elsevier, San Diego 19. Kurtz SM, Edidin AA, Bartel DL (1997) The role of backside polishing, cup angle, and polyethylene thickness on the contact stresses in metal-backed acetabular components. J Biomech 30(6):639–642. doi:10.1016/S0021–9290(96)00181–9 20. Kurtz SM, Gawel HA, Patel JD (2011) History and systematic review of wear and osteolysis outcomes for ﬁrst-generation highly crosslinked polyethylene. Clin Orthop Relat Res 469(8):2262–2277. doi:10.1007/s11999–011–1872–4 21. Livermore J, Ilstrup D, Morrey B (1990) Effect of femoral head size on wear of the polyethylene acetabular component. J Bone Joint Surg Am 72(4):518–528 22. Lundberg HJ, Pedersen DR, Baer TE, Muste M, Callaghan JJ, Brown TD (2007) Effects of implant design parameters on ﬂuid convection, potentiating third-body debris ingress into the bearing surface during THA impingement/subluxation. J Biomech 40(8):1676–1685. doi:10.1016/j.jbiomech.2007.01.021 23. Marshall A, Ries MD, Paprosky W (2008) Implant Wear Symposium 2007 Clinical Work Group. How prevalent are implant wear and osteolysis, and how has the scope of osteolysis changed since 2000? J Am Acad Orthop Surg 16(Suppl 1):S1–S6 24. Oral E, Godleski Beckos C, Malhi AS, Muratoglu OK (2008) The effects of high dose irradiation on the cross-linking of vitamin E-blended ultrahigh molecular weight polyethylene. Biomaterials 29(26):3557–3560. doi:10.1016/j.biomaterials.2008.05.004 25. Schmalzried TP, Brown IC, Amstutz HC, Engh CA, Harris WH (1999) The role of acetabular component screw holes and/or screws in the development of pelvic osteolysis. Proc Inst Mech Eng H 213(2):147–153. doi:10.1243/0954411991534861 26. Thomas GER, Simpson DJ, Mehmood S, Taylor A, McLardy-Smith P, Gill HS, Murray DW, Glyn-Jones S (2011) The seven-year wear of highly cross-linked polyethylene in total hip arthroplasty: a double-blind, randomized controlled trial using radiostereometric analysis. J Bone Joint Surg Am 93(8):716–722. doi:10.2106/JBJS.J.00287 27. ASTM F 2183–02 (2003) Test method for small punch testing of ultra-high molecular weight polyethylene used in surgical implants. Annual book of ASTM standards, vol 13.01. ASTM International, West Conshohocken. doi:10.1520/F2183–02R08

Part III Metal Articulations

Metal-on-Metal Bearings in Hip Surgery: The London Implant Retrieval Centre Experience

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John Skinner, Alister Hart, and Ashley Matthies

7.1 Advantages and Disadvantages of Metal-on-Metal Bearings in Hip Surgery Modern metal-on-metal bearings for hip replacement were reintroduced approximately 15 years ago in order to provide an alternative wear resistant bearing suitable for large diameter hip resurfacing and total hip replacement. Both types of metal-on-metal hip use a thin one-piece acetabular cup for use with either a resurfacing femoral head or a stemmed modular femoral head. There were many proposed advantages for the use of large diameter metal-on-metal hip resurfacing. This included preservation of femoral bone stock and therefore easier revision surgery in young patients that are likely to outlive their primary hip replacement [10, 29]. Additionally, it has been reported that the use of larger femoral diameters allows patients to retain a more normal gait pattern, increased range of motion and reduced rates of dislocation [10, 29]. Large diameter total hip replacements were introduced to provide all of the same beneﬁts of an increased head size, whilst allowing easier primary surgery, easier revision of a hip resurfacing device and a large diameter alternative for patients not suitable for resurfacing. Despite the proposed advantages of metal-on-metal as a bearing surface for both total and resurfacing hip replacement, there remains a problem with higher than expected clinical failure rates and wear-related soft tissue reactions. According to the latest joint registry data [27], failure rates vary signiﬁcantly between designs and are higher for large diameter devices compared to hip resurfacing devices. Wear-related soft tissue reactions were ﬁrst reported several decades ago and have been reported in patients with metal-on-metal hip replacement as well as conventional metalon-polyethylene hip replacement. Although undoubtedly representing a reaction to metal

J. Skinner (*) • A. Hart • A. Matthies Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK e-mail: [email protected]

K. Knahr (ed.), Total Hip Arthroplasty, DOI 10.1007/978-3-642-27361-2_7, © 2012 EFORT

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wear debris, the pathogenesis of these reactions remains largely unclear. It is unknown whether these represent a simpler dose-response reaction or whether an underlying patient sensitivity factor is responsible. In response to higher than expected failure rates and concerns regarding soft tissue reactions, the Medicines and Healthcare products Regulatory Agency (MHRA) issued a Medical Device Alert in April 2010, concerning the safety of all metal-on-metal hip devices [24, 25]. It was suggested that all patients be reviewed regularly, to include measurement of blood metal ion levels and cross-sectional imaging to investigate the soft tissues. Continued evidence from joint registries of unacceptably high failure rates [27] led to two further medical device alerts and then the market withdrawal of the articular surface replacement (ASR) hip resurfacing and ASR XL systems later in 2010 [24, 25]. By collecting and analysing retrievals and correlating this with clinical data, it may be possible to improve our understanding of the mechanisms responsible for the higher than predicted failure rates. This is essential if we are to improve the treatment and follow-up of the estimated one million patients that have received a metal-on-metal hip replacement in the past 10 years. Throughout the remainder of this chapter, we discuss the clinical relevance of high wear and raised metal ion levels and the current understanding of the factors responsible for high wear and wear-related complications arising in patients with metal-on-metal hip replacements.

7.2 Wear and Metal Ion Levels in Metal-on-Metal Hip Replacement It is well documented that cobalt and chromium ion levels in the blood and synovial ﬂuid correlate well with component wear rates and that metal ions can be used as a surrogate marker for wear [5].

7.2.1 Clinical Relevance of Raised Metal Ion Levels There have been numerous clinical studies quoting metal ion levels from either serum or whole blood samples of patients with metal-on-metal hip replacement. Levels have been reported using two different unit systems, parts per billion (ppb) and micrograms per litre (mg/L), and it is important to ﬁrst appreciate that these are interchangeable (i.e. 1 ppb is equal to 1 mg/L). There is mounting evidence that raised metal ion levels are associated with failure and the incidence of painful soft tissue reactions [12, 15, 20, 28]. In our experience, whole blood cobalt and chromium levels in patients with well-functioning hips are approximately half those seen in patients presenting with painful prostheses (Fig. 7.1) [12, 15]. Similarly, patients revised with a soft tissue mass, or pseudotumour, demonstrated ion levels twice those of patients revised without soft tissue pathology (Fig. 7.2) [22, 23]. However, there is, as yet no deﬁned cut-off between a low and high metal ion level, and it must be emphasised that metal ion levels cannot be used as a screening test in asymptomatic patients.

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A comparison of whole blood metalion levels between patients with well functioning and symptomatic Birmingham hip resurfacings

Log10 whole blood metalion levels (ppb)

2.5 2.0 1.5 1.0 0.5 0.0 −0.5 −1.0 Well functioning

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Fig. 7.1 A comparison of whole blood chromium and cobalt levels between patients with well-functioning and painful Birmingham hip resurfacings. Patients presenting with unexplained pain had both chromium and cobalt levels double those seen in the well-functioning group

Log10 whole blood metalion levels (ppb)

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A comparison of whole blood metalion levels between patients revised with a pseudotumour and those revised without any soft tissue pathology

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Fig. 7.2 A comparison of whole blood chromium and cobalt levels between patients revised with no soft tissue abnormalities and those revised with a preoperative diagnosis of pseudotumor

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We have previously investigated the sensitivity and speciﬁcity of whole blood metal ion levels to discriminate between patients with asymptomatic well-functioning metal-onmetal hips and patients presenting with unexplained hip pain [13, 14, 16, 17]. The optimal cut-off for a maximum metal ion level was identiﬁed as 4.97 ppb. This level had a sensitivity of 0.63 and speciﬁcity of 0.86. A maximum metal ion level of 7 ppb has been suggested by the MHRA as a threshold for further investigation to include cross-sectional imaging of the soft tissues [24, 25]. This level provided high speciﬁcity (0.89) but a relatively low sensitivity (0.52). Whilst there is currently no evidence that there is a certain metal ion level that provides both suitable sensitivity and speciﬁcity, blood metal ion levels are likely to remain an important adjunct to clinical assessment and imaging of the symptomatic patient.

7.2.2 Measuring Wear of Retrieved Metal-on-Metal Components Wear of the bearing surfaces and of the head-stem junction can be measured using either a roundness measurement machine [19, 20, 22, 23] or a coordinate measuring machine [2, 26]. Both of these are suitable; however, few studies have used a validated method for measuring and calculating linear (two dimensional) or volumetric (three dimensional) wear. Further to this, variation in methods has not enabled comparison of the published data. We have identiﬁed a number of problems when attempting to geometrically measure wear. First, there is the problem of not knowing the original component dimensions and shape. ISO 14242-2 speciﬁes that a component is manufactured with a form error of less than 10 m, and from our experience, we know that component wear is often of a similar or smaller magnitude to the form error. Furthermore, components have a diametric size tolerance of 0–0.2 mm, and therefore, the data supplied by the manufacturer represent only a nominal value. In our retrieval laboratory, we have used both a roundness measurement machine [22, 23, 32] and CMM [2] to measure linear wear of metal-on-metal hip components. As a result of measurement uncertainty, it is beneﬁcial to report linear wear since any error in measurement is likely to be ampliﬁed when calculating wear volumes in three dimensions. Uncertainty in wear measurement may arise due to (1) the accuracy of the measuring instrument being used, (2) the method for estimating the unworn shape and size of the component, (3) the number and distribution of measurement points and (4) the accuracy of the alignment method. We have reviewed the published methods used to calculate volumetric wear, and after taking into account the effect of potential sources of measurement error, we can predict that in several studies, the volumetric wear may have been overestimated by up to several cubic millimetres [2]. It is also recognised that it is easier to approximate the pre-worn shape of the component from linear two-dimensional roundness proﬁles. Future studies of wear require more detailed description of methodology to make it possible for readers to determine the reliability of the data and so that results can be compared between studies. This is essential if we are to understand why and how patients with metal-on-metal hip replacements suffer from wear-related complications.

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7.2.3 Overview of the Factors Responsible for High Bearing Surface Wear and Raised Metal Ion Levels The wear performance of metal-on-metal hips is multifactorial and is likely to be determined by various surgical-, patient-, and design-speciﬁc factors. The majority of these factors are closely associated with the amount of femoral cover and the risk of edge loading (Fig. 7.3). Edge loading is a commonly cited mechanism of wear in metal-on-metal hips [22, 23, 26], in which the contact area between the two components extends over the rim of the cup. Edge contact has a much increased peak contact pressure, resulting in up to a 25-fold increase in component wear rate. As a result, the wear performance of metal-onmetal hip replacements is extremely sensitive to slight changes in component position and design. A mathematical model can be used to calculate the distance from the contact patch to the rim of the cup. This can be used to describe the interaction of multiple variables and the effect on femoral cover and the risk of edge loading. The ﬁrst stage of this mathematical model is to determine the radius (size) of the contact area between the head and the cup, which can easily be done by applying Hertz theory of elastic contact. The factors that determine the radius are the material properties of cobalt-chromium, the joint reaction force and the clearance of the bearing. The distance from the edge of the contact patch to the rim of the cup can then be calculated based on two directional vectors: (1) the anatomical cup orientation through the pole and (2) the joint reaction force. The direction of the cup orientation vector is based on rotations deﬁned by the anatomical orientation of the cup (version and inclination). The orientation of the joint reaction force vector is based on Bergman’s data on standing up [1]. The vector dot product can be calculated between the two vectors, giving the angle between them in a plane that passes through the centre of head and cup. From greater circle theory,

CPRD

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Fig. 7.3 Schematic diagram illustrating key design (clearance and cup articular arc angle (CAAA)) and surgical (cup inclination angle) variables that affect the contact patch to rim distance (CPRD). Figures (a), (b) and (c) clearly show how changes in these variables result in an increased chance of edge loading

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the shortest distance between two points on a sphere is in the plane that passes through the centre of the sphere. As the angle between the two force vectors is known, the distance between the reaction force and the rim of the cup can be calculated. The radius of the contact patch is predetermined using Hertz theory, as described above. The radial distance was then subtracted from the distance between the reaction force and cup to determine the distance from the edge of the contact patch to the rim of the cup. This model identiﬁes several surgical-, design- and patient-speciﬁc variables associated with the risk of edge loading, which will be discussed in greater depth throughout this chapter. This model also provides a means of calculating the effect of variation in any of these parameters on the theoretical risk of edge contact (Figs. 7.4, 7.5, 7.6, 7.7). It is important to emphasise that in our experience of wear measurement, a large number of hips have been edge worn, but the majority remains low wearing (both components wearing at less than 5 mm/year) [22, 23].

7.2.4 The Importance of Good Surgical Positioning Surgical positioning of the components is one of the key determinants of wear and metal ion levels. It is widely accepted that adverse acetabular position, particularly excessive inclination, is associated with increased wear of the components [13, 14, 16, 17, 26] and raised blood cobalt and chromium levels in the blood [4, 13, 14, 16, 17, 21]. In addition to wear performance, there appears to be a strong correlation between cup inclination angle and revision [4, 11]. In our experience with blood metal ion levels, we have observed a signiﬁcant positive correlation with the angle of cup inclination and a signiﬁcant negative correlation with the angle of version [13, 14, 16, 17]. Similarly, component wear was positively correlated with the angle of cup inclination [13, 14, 16, 17]. However, the relationship between wear and the angle of version is more complicated. Whilst we have observed a weak positive correlation [13, 14, 16, 17] between the two, it is likely that cup inclination is the dominant variable. This is in agreement with the theoretical model described earlier concerning the amount of femoral cover, in which a single unit increase in inclination has a greater effect on the distance between the contact patch and the rim of the cup than a single unit increase in version. Impingement of the femoral neck (or stem) on the rim of the cup is another wellaccepted cause of edge loading in hard-on-hard bearings. Subluxation and subsequent relocation of the femoral head result in edge loading perpendicular to the point of impingement. In our retrieval collection, we have seen several cases in which either insufﬁcient inclination or version has resulted in anterior impingement, edge loading and subsequently high component wear rates and raised blood metal ion levels [22, 23]. Much less is known concerning the importance of femoral or translational positional factors such as horizontal femoral offset, femoral version, pelvic tilt and leg-length discrepancy. Currently, there is only one published study investigating the effect of only one of these, femoral version, on metal ion levels and component wear [13, 14, 16, 17]. No signiﬁcant correlation was shown. Given that component wear is determined largely by the location of the contact area and its proximity to the rim of the cup, it is likely that all posi-

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The effect of cup position on the contact patch to rim distance for a 50 mm cup with a 160° arc of cover

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Fig. 7.4 Figure illustrating how excessive cup inclination and version both increase the chance of edge loading The effect of femoral diameter on the contact patch to rim distanc. The cup has a 160° arc of cover and is 15° anterverted.

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Fig. 7.5 Figure illustrating how reduced femoral diameter increases the chance of edge loading

tional variables contribute to the wear performance of metal-on-metal hip prostheses. Further investigation of these is necessary, but requires computer tomography imaging and three-dimensional reconstruction for reliable accurate measurement.

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Fig. 7.6 Figure illustrating how a reduced cup articular arc angle (or arc of cover) increases the chance of edge loading The effect of clearance on the radius of the head−cup contact patch

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Fig. 7.7 Figure showing the calculated radius of the contact patch for any given bearing clearance (assuming that the joint reaction force and material properties are constant). This shows how low clearance designs have a larger contact area, and therefore are more likely to edge load

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7.2.5 The Importance of Component Design It is widely reported that component wear rates and blood metal ion levels vary depending on the speciﬁc metal-on-metal hip design used. For example, it has been shown that patients with a Birmingham hip resurfacing (BHR) are likely to have lower blood metal ion levels than those with an articular surface replacement (ASR) [21]. Similarly, retrieved BHR components are more likely to be lower wearing [32]. In Figs. 7.8 and 7.9, we show a comparison of metal ion levels and component wear rates for four commercially available metal-on-metal hip systems. The variation in wear between the different designs can be explained by variation in a number of speciﬁc design features. Unlike conventional polyethylene cups, the one-piece cups used for metal-on-metal hip replacement are less than hemispherical (less than a 180 arc). Furthermore, the portion of a hemisphere occupied by the cup varies between each hip design, and for several designs, varies with size. In the literature, this design feature has been referred to as the ‘cup articular arc angle’ [32], the ‘arc of cover’ [21] and the alpha (a) angle [31]. It is also widely accepted that this is the principal reason why some hip designs, such as the Articular Surface Replacement (ASR), are more sensitive to component position and more often found to be higher wearing. The articular arc angles of the commercially available onepiece metal cups range between 149° and 165°. The articulating surface of the ASR stops approximately 2.5 mm below the rim of the cup, and this results in a reduction in the articular arc angle. The effect of reducing the arc of cover is similar to the effect of increasing cup inclination in that the amount of femoral cover is reduced and the contact area is

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Linear acetabular cup wear rates for the four most common hip designs collected at the London Implant Retrieval Centre

Log10 linear cup wear rate (µm/year)

2.5 2.0 1.5 1.0 0.5 0.0 −0.5 −1.0

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Fig. 7.8 A comparison of cup wear rates between the four most common designs collected at the London Implant Retrieval Centre

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J. Skinner et al. A comparison of wholw blood metalion levels for the four most common hip designs collected at the London Implant Retrieval Centre

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Fig. 7.9 A comparison of whole blood chromium and cobalt levels between the four most common designs collected at the London Implant Retrieval Centre

brought closer to the edge of the cup. Therefore, as discussed previously, the theoretical chance of edge loading varies between designs. The radial clearance is another design variable that affects the tribology of metal-onmetal hips. Clearance refers to the difference in radii between the cup and head components, and again, this varies signiﬁcantly between different designs, ranging between 45 and 110 mm. The Hertz theory of elastic contact can be applied to hard-on-hard bearings to describe the relationship between the size (width) of the contact area and the peak contact pressures applied across the joint. Whilst reduced clearance results in a more conformal contact between the two components and therefore reduced contact pressures, the area of the contact is larger and therefore brought closer to the rim of the cup. Although the optimal clearance for a hard-on-hard bearing is not known, this represents a balance between reducing peak contact pressures without greatly increasing the chance of edge loading. Again, the ASR has the lowest clearance of all the new generation metal-on-metal hips, and in addition to the reduced arc of cover for this design, it is likely to signiﬁcantly increase the chance of edge loading. Another design feature of the ASR cup that reduces wear performance is the radius of the rim chamfer [32]. Not only is the rim stepped, reducing the amount of femoral cover, but the radius of the rim is smaller (0.2 mm) than any other currently available one-piece metal cup design (typically >0.5 mm). This reduced radius further compounds the effect of edge loading on wear. For the ASR, the peak contact pressures experienced during edge loading are likely to be even higher. It is likely that other component-speciﬁc features are important in wear performance, and this may include differences in metallurgy. It will be important to continue investigating retrievals and correlating ﬁndings with clinical data in order to improve future designs.

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7.2.6 Patient Factors Affecting Wear Smaller patients can only accommodate smaller diameter hip replacements, and it is known that smaller femoral diameter is associated with both increased wear and metal ion levels and increased clinical failure rates. Other potential patient-speciﬁc factors are least well understood. However, it is likely that gait patterns and certain activities are more likely to cause edge wear and result in higher wear and metal ion levels. Bergman et al. have previously demonstrated the variability in the orientation of the joint reaction force for common daily activities [1]. Certain activities, such as sitting down, are associated with a joint reaction force passing through the bearing closer to the rim of the cup. Additionally, there is likely to be a signiﬁcant amount of patient variability for each activity, and therefore for some patients they are more likely to edge load their hip replacement.

7.2.7 Material Loss from Large Diameter Metal-on-Metal Total Hip Replacement In addition to wear of the bearing surface, in patients with total hip replacement devices, there may be additional material loss from the head-stem junction either as a result of wear or corrosion [3]. It has been shown in a randomised controlled trial that both cobalt and chromium levels are signiﬁcantly higher in patients with a metal-on-metal total hip replacement compared to those with a hip resurfacing device from the same manufacturer. We have observed macroscopic corrosion at the head-stem interface at revision surgery in over 90% of cases (Fig. 7.10). Using a peer-reviewed classiﬁcation system [8], over 60% of the retrieved components were at least moderately corroded. It is likely that both galvanic and mechanically assisted crevice corrosion mechanisms are likely to be involved. On our components, and this is corroborated by evidence from other centres [3, 21], there appears to be signiﬁcant mechanical wear, with depths of up to 40 mm, occurring at the taper junction.

Fig. 7.10 (a) A photograph showing macroscopic evidence of corrosion at the femoral taper junction of a large diameter metal-on-metal total hip replacement, and (b) a photograph of a stem also showing evidence of corrosion at the taper

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The clinical performance of large diameter metal-on-metal total hip replacement is known to be worse than hip resurfacing, but the full consequence of an increase in metal burden is unknown. There have been no studies comparing the rates of adverse soft tissue reaction between the two types of hip prosthesis. However, comparison can be made to the clinical problems and high early failure rates reported by Donell et al. for the DePuy Ultima hip replacement, in which excessive corrosion of the stem was frequently observed [6].

7.3 Imaging in Metal-on-Metal Hip Replacements Imaging of both the components and soft tissues is an important aspect of the clinical assessment of the patient with a symptomatic metal-on-metal hip.

7.3.1 Measuring Component Position Reliable measurement of component position is essential given that, compared to metalon-polyethylene, metal-on-metal hip prostheses are less forgiving of suboptimal position, particularly cup position. As previously mentioned, cup position is one of the most signiﬁcant factors affecting component wear and metal ion levels. Plain radiograph has been the most widely used imaging modality to measure cup inclination and version. Many studies have used EBRA computer software to measure cup position, but this has not been validated, nor been recommended by the producer, for use in metal-on-metal hip replacement. Additionally, even for cases in which good quality anteroposterior and lateral radiographs have been taken, cup position, and particularly version, is notoriously difﬁcult to measure in patients with large diameter metal-on-metal hips [12, 15]. We have previously compared radiographic measurements of inclination and version with those measured from three-dimensional reconstructed computer tomography (CT) images. Bland-Altman analysis found two standard deviation limits of agreements of +7 to −15° for inclination angle and +16 to −31° for cup version angle [12, 15]. This was attributed to the large diameter metal femoral head obscuring the margins of the cup as well as problems with image magniﬁcation and perspective distortion. We recommend that reliable and accurate measurement of cup position can only be made from CT images. Low radiation dose (1.7 mSv) CT scans can be performed with 0.75-mm collimation (high resolution) and artefact minimisation software (16 bit data processed on an extended scale), both of which provide the level of detail required to separate the metallic cup face from the large diameter femoral head. The Digital Imaging and Communications in Medicine (DICOM) images of the CT scan can then be reconstructed in three dimensions, using computer software, and the position of the pelvis can be aligned with the anterior pelvic plane (APP) (providing a standard frame of reference, against which cup positional angles can be measured). The plane of the cup face can then be labelled using points selected around the cup edge (Fig. 7.11). The plane of the cup face can then be compared

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Fig. 7.11 An example of a reconstructed CT image of an acetabular cup

with (1) an axial plane orthogonal to the APP to measure cup inclination and (2) a sagittal plane orthogonal to both the axial and AP planes to measure cup version.

7.3.2 Imaging the Soft Tissues Given the recent recommendations by the MHRA, adequate imaging of the soft tissues is essential. Both plain radiograph and computer tomography scanning are limited for this purpose, and it is widely accepted that ultrasound and metal artefact reduction sequence (MARS), magnetic resonance imaging (MRI), are the best modalities for assessment of the soft tissues. Although not yet proven, it is likely that MRI provides a higher sensitivity for diagnosing soft tissue destruction and inﬂammatory masses (pseudotumours).

7.4 Soft Tissue Reactions in Patients with Metal-on-Metal Hip Replacements The term pseudotumour was ﬁrst introduced in 2008 to describe cystic and solid inﬂammatory soft tissue masses in patients with metal-on-metal hip resurfacing devices [28]. Currently, there are numerous radiological, operative and histological deﬁnitions being used to describe these adverse soft tissue reactions to metal wear debris. The radiographic terms include pseudotumour [28], cyst, bursa, inﬂammatory lesion and effusion. Other

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studies describe an operative appearance of metallosis [18], which refers to a macroscopic staining of the tissues. Histological terms include aseptic lymphocytic-vasculitis-associated lesion (ALVAL) [33] and lymphocyte-dominant immune reaction (LYDIA) [33]. Most recently, Langton et al. have introduced an umbrella term, adverse reaction to metal debris (ARMD), to include many of the aforementioned deﬁnitions. However, it is important to emphasise that there is currently no consensus in the literature deﬁning the boundaries of each term, and therefore, it remains difﬁcult to correlate and results from different centres.

7.4.1 Factors Associated with a Soft Tissue Reaction or Pseudotumour Several studies have now reported associations between increased component wear, raised metal ion levels and the incidence of adverse soft tissue reactions, or pseudotumours [19, 21–23]. There has only been one prospective study investigating the risk factors associated with the development of a pseudotumour [7]. This study identiﬁed gender as the main risk factor. In a case-control study, we have found pseudotumours to be equally as common in asymptomatic patients as in those presenting to our clinic with a painful metal-on-metal hip. In both groups, pseudotumours were diagnosed in approximately 60% of patients [13, 14, 16, 17]. In our experience, lesions are of two main forms, ﬂuid collections (cysts) and more rarely solid masses [30]. Figure 7.12 illustrates the operative and radiological appearance of a pseudotumour. In a study of 100 revisions, we compared patients revised with a pseudotumour to patients revised with no soft tissue pathology seen on MRI. Although pseudotumour was associated with higher pre-revision blood metal ion levels and higher wear rates of the retrieved components, greater than 40% patients with a pseudotumour had metal ion levels below 7 ppb, component wear rates below 5 mm per year and a well-positioned acetabular component. Additionally, the proportion of patients with a pseudotumour was similar for those with an acceptable cup position (67%) when compared to those with a poorly

Fig. 7.12 (a) A photograph illustrating the operative appearance of a solid inﬂammatory soft tissue mass, and (b) an MR image illustrating the radiological appearance of a cystic inﬂammatory lesion

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Metal-on-Metal Bearings in Hip Surgery: The London Implant Retrieval Centre Experience Distribution of pseudotumour diagnoses according to hip design

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Pseuodtumour No pseuodtumour

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30

20

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0 Adept

ASR

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Fig. 7.13 A stacked bar chart showing that patients with any design of metal-on-metal hip are susceptible to pseudotumours

positioned cup (66%) [22, 23]. We have also diagnosed pseudotumours on MRI scan in patients with all of the metal-on-metal hip designs that have been referred to our centre (Fig. 7.13). In light of our experience, we suggest that there is an underlying biocompatibility issue with metal-on-metal hip replacement and that an unidentiﬁed patient susceptibility factor is responsible for almost half of failures due to unexplained pain and adverse soft tissue reactions. Although patients with any designs are susceptible to developing a soft tissue reaction, it is likely that the risk is increased in patients who have a higher wearing hip design, such as the ASR, in situ.

7.4.2 Revision of the Patient with a Soft Tissue Reaction There have been few studies documenting the outcomes of revision surgery in patients having suffered soft tissue destruction adjacent to their metal-on-metal hip. One previous study has shown that patients revised due to pseudotumour had signiﬁcantly worse Oxford Hip Scores compared to patients undergoing revision due to other causes [9]. In this group of patients, the authors also noted a high incidence of post-revision complications, including femoral nerve palsy, recurrent dislocation, component loosening and recurrent pseudotumour. It has been suggested that early revision in patients suffering adverse soft tissue reactions may improve outcomes. However, there is no clear evidence describing an overall threshold for revision. The natural evolution of pseudotumours remains unknown, but it is

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likely that these reactions are progressive, and by earlier identiﬁcation and management it may be possible to prevent catastrophic soft tissue destruction and improve the outcome of revision surgery.

7.5 Summary Despite the proposed beneﬁts of metal-on-metal, clinical failure rates have been higher than expected, and there remains a problem with soft tissue reactions associated with wear of the components. Given the evidence that soft tissue reactions are not uncommon in patients with well-positioned, low wearing components, it is essential to provide close surveillance of all patients with metal-on-metal hip replacements. Whilst joint registries provide the ideal source for data concerning clinical rates of failure, studying retrievals may help us to understand the mechanisms leading to failure and improve future hip design.

References 1. Bergmann G, Deuretzbacher G, Heller M, Graichen F, Rohlmann A, Strauss J, Duda GN (2001) Hip contact forces and gait patterns from routine activities. J Biomech 34:859–871 2. Bills PJ, Racasan R, Underwood RJ, Cann P, Skinner J, Hart AJ, Jiang X, Blunt L (2011) Volumetric wear assessment of retrieved metal-on-metal hip prostheses and the impact of measurement uncertainty. Wear (in press) 3. Bolland B, Culliford D, Langton D, Millington J, Arden N, Latham J (2011) High failure rates with a large diameter hybrid metal-on-metal total hip replacement: clinical, radiological and retrieval analysis. J Bone Joint Surg Br 93:608–615 4. De Haan R, Pattyn C, Gill HS, Murray DW, Campbell PA, De Smet K (2008) Correlation between inclination of the acetabular component and metal ion levels in metal-on-metal hip resurfacing replacement. J Bone Joint Surg Br 90:1291–1297 5. De Smet K, De Haan R, Calistri A, Campbell PA, Ebramzadeh E, Pattyn C, Gill HS (2008) Metal ion measurement as a diagnostic tool to identify problems with metal-on-metal hip resurfacing. J Bone Joint Surg Am 90:202–208 6. Donell S, Darrah C, Nolan J, Wimhurst J, Toms A, Barker T (2010) Early failure of the ultima metal-on-metal total hip replacement in the presence of normal plain radiographs. J Bone Joint Surg Br 92:1501–1508 7. Glyn-Jones S, Pandit H, Kwon YM, Doll H, Gill HS, Murray DW (2009) Risk factors for inﬂammatory pseudotumor formation following hip resurfacing. J Bone Joint Surg Br 91-B:1566–1574 8. Goldberg JR, Gilber JL, Jacobs JJ, Bauer TW, Paprosky W, Leurgans S (2002) A multicenter retrieval study of the taper interfaces of modular hip prostheses. Clin Orthop Relat Res 401:149–161 9. Grammatopolous G, Pandit H, Kwon YM, Gundle R, McLardy-Smith P, Beard DJ, Murray DW, Gill HS (2009) Hip resurfacings revised for inﬂammatory pseudotumor have a poor outcome. J Bone Joint Surg Br 91-B:1019–1024 10. Haddad FS, Thakrar RR, Hart AJ, Skinner JA, Nargol AVF, Nolan JF, Gill HS, Murray DW, Blom AW, Case P (2011) Metal-on-metal bearings – the evidence so far. J Bone Joint Surg Br 93:572–579

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11. Hart AJ, Buddhev P, Winship P, Faria N, Powell J, Skinner J (2008) Cup inclination angle of greater than 50 degrees increases whole blood concentrations of cobalt and chromium ions after metal-on-metal hip resurfacing. Hip Int 18:212–219 12. Hart AJ, Dandachli W, Schleuter-Brust K, Henckel J, Cobb JP (2009) Large ball metal-onmetal hips obscure cup angle measurement on plain radiographs. Hip Int 19-4:323–329 13. Hart AJ, Ilo K, Underwood R, Cann P, Henckel J, Lewis A, Cobb J, Skinner J (2011) The relationship between the angle of version and rate of wear of retrieved metal-on-metal resurfacings. J Bone Joint Surg Br 93-B:315–320 14. Hart AJ, Sabah S, Bandi A, Tarrasole P, Maggiore P, Sampson B, Skinner JA (2011) Sensitivity and speciﬁcity of blood cobalt and chromium metal ions for predicting failure of metal-onmetal hip arthroplasty. J Bone Joint Surg [Br] 93:1308–1313 15. Hart AJ, Sabah S, Henckel J, Lewis A, Cobb J, Sampson B, Skinner JA (2009) The painful metal-on-metal hip resurfacing. J Bone Joint Surg Br 91:835–842 16. Hart AJ, Satchithananda K, Liddle A, Sabah SA, McRobbie D, Henckel J, Skinner J, Mitchell A (2011) Pseudotumours following well-functioning metal-on-metal hip arthroplasty: a case– control study using three dimensional computerized tomography and magnetic resonance imaging. J Bone Joint Surg [Am] (in press) 17. Hart AJ, Skinner JA, Henckel J, Sampson B, Gordon F (2011) Insufﬁcient acetabular version increases blood metal ion levels after metal-on-metal hip resurfacing. Clin Orthop Relat Res I469:2590–2597 18. Korovessis P, Petsinis G, Repanti M, Repantis T (2006) Metallosis after contemporary metal-on-metal hip arthroplasty: ﬁve- to nine- year follow-up. J Bone Joint Surg Am 88:1183–1191 19. Kwon YM, Glyn-Jones S, Simpson DJ, Kamali A, McLardy-Smith P, Gill HS, Murray DW (2010) Analysis of wear of retrieved metal-on-metal hip resurfacing implants revised due to pseudotumors. J Bone Joint Surg Br 92-B:356–361 20. Langton DJ, Jameson SS, Joyce TJ, Hallab NJ, Natu S, Nargol AVF (2010) Early failure of metal-on-metal bearings in hip resurfacing and large diameter total hip replacement: a consequence of excess wear. J Bone Joint Surg Br 92:38–46 21. Langton DJ, Joyce TJ, Jameson SS, Lord J, Orsouw MV, Holland JP, Nargol AVF, De Smet KA (2011) Adverse reaction to metal debris following hip resurfacing: the inﬂuence of component type, orientation and volumetric wear. J Bone Joint Surg Br 93-B:164–171 22. Matthies A, Skinner JA, Osmani H, Henckel J, Hart AJ (2011) Pseudotumors are common in well-positioned, low wearing metal-on-metal hips. Clin Orth Rel Res (in press) 23. Matthies A, Underwood R, Cann PM, Ilo K, Nawaz Z, Skinner J, Hart AJ (2011) Retrieval analysis of 240 metal-on-metal hip components, comparing modular total hip replacement with hip resurfacing. J Bone Joint Surg Br 93:307–314 24. MHRA Medicines and Healthcare Products Regulatory Agency (MHRA). Medical device alert: all metal-on-metal (MoM) hip replacements (MDA/2010/033). http://www.mhra.gov.uk/. Accessed 12 Oct 2011 25. MHRA Medicines and Healthcare Products Regulatory Agency (MHRA). Medical device alert: ASR™ hip replacement implants manufactured by DePuy International Ltd (MDA/2010/069). http://www.mhra.gov.uk/. Accessed 12 Oct 2011 26. Morlock MM, Bishop N, Zustin J, Hahn M, Ruther W, Amling M (2008) Modes of implant failure after hip resurfacing: morphological and wear analysis of 267 retrieval specimens. J Bone Joint Surg Am 90-A:89–95 27. National Joint Registry UK. 7th Annual Report 2010. http://www.njrcentre.org.uk/. Accessed 12 Oct 2011 28. Pandit H, Glyn-Jones S, McLardy-Smith P, Gundle R, Whitwell D, Gibbons CLM, Ostlere S, Athanasou N, Gill HS, Murray DW (2008) Pseudotumours associated with metal-on-metal hip resurfacings. J Bone Joint Surg Br 90:847–851 29. Quesada MJ, Marker DR, Mont MA (2008) Metal-on-metal hip resurfacing: advantages and disadvantages. J Arthroplasty 23(7):69–73

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30. Sabah SA, Mitchell AWM, Henckel J, Sandison A, Skinner JA, Hart AJ (2011) Magnetic resonance imaging ﬁndings in painful metal-on-metal hips – a prospective study. J Arthroplasty 26:71–76 31. Shimmin AJ, Walter WL, Esposito C (2010) The inﬂuence of the size of the component on the outcome of resurfacing arthroplasty of the hip: a review of the literature. J Bone Joint Surg Br 92-B:469–476 32. Underwood R, Matthies A, Cann P, Skinner J, Hart AJ (2011) A comparison of explanted articular surface replacement and Birmingham hip resurfacing components. J Bone Joint Surg Br 93-B:1169–1177 33. Willert HG, Buchhorn GH, Fayyazi A, Flury R, Windler M, Koster G, Lohmann CH (2005) Metal-on-metal bearings and hypersensitivity in patients with artiﬁcial hip joints. A clinical and histomorphological study. J Bone Joint Surg Am 87:28–36

Total Hip Arthroplasty with a Large-Diameter Metal-on-Metal Cup (Durom) and a Standard Stem: Short-Term Results

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Panayiotis Christofilopoulos, Anne Lübbeke, Charles Berton, Alexandre Lädermann, Martin Berli, Constantinos Roussos, Alexis Bonvin, Robin Peter, and Pierre Hoffmeyer

8.1 Introduction LHMOM has been used as part of a conventional THA advocating superior results concerning dislocation rate and survival [21]. We had used this implant conﬁguration in Geneva since 2004. When the ﬁrst data showing some concerns about high revision rates appeared [15], we decided to stop using this implant and conduct a follow-up study of our cohort of patients.

8.2 Materials and Methods We conducted a study including all primary THAs with the Durom acetabular component (Durom, Zimmer GmbH, Winterthur, Switzerland), a large-diameter metal-on-metal articulation and a standard stem operated upon between September 2004 and September 2008 at a large teaching hospital. The study population is part of an ongoing hospital-based prospective THA cohort started in 1996 and followed longitudinally. The Durom acetabular component is a monoblock, ﬂattened hemispherical implant with a constant wall thickness of 4 mm (3.7 mm of Metasul and 0.3 mm of a pure titanium, plasma-sprayed coating, Porolock TiVPS) and a large-diameter head, which is 8 mm smaller than the outside diameter of the acetabular component and 6 mm smaller than its nominal size, with a metal-on-metal articulation (Metasul, Zimmer GmbH, Winterthur, Switzerland). The opening angle (the subtended angle) was ﬁxed at 165° instead of 180°

P. Christoﬁlopoulos (*) • A. Lübbeke • C. Berton • A. Lädermann • M. Berli • C. Roussos • A. Bonvin • R. Peter • P. Hoffmeyer Département de Chirurgie, Chirurgie Orthopédique et Traumatologie de l’appareil Moteur, Hôpitaux Universitaires de Genève, Rue Gabrielle-Perret-Gentil 4, 1211 Genève 14, Switzerland e-mail: panayiotis.christoﬁ[email protected] K. Knahr (ed.), Total Hip Arthroplasty, DOI 10.1007/978-3-642-27361-2_8, © 2012 EFORT

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for traditional THA bearings. The acetabulum was underreamed by 2 mm as recommended by the manufacturer and the component impacted into place. Primary ﬁxation was completed with three equatorial ﬁns. In case of a cemented stem (Müller CoCr straight stem; Zimmer Ltd., Winterthur, Switzerland), a third generation technique with pulsed lavage and an intramedullary plug was performed. Each procedure was carried out through a posterior approach or through a lateral transgluteal approach (without osteotomy of the greater trochanter), according to the surgeon’s habits. Gentamicin-loaded bone cement was employed in all cases with cemented stem implants. All patients received a single-dose second generation cephalosporin before induction and standard thrombo-prophylaxis. The procedures were performed in an ultraclean air laminar ﬂow operating room by surgeons with different degrees of experience. Outcomes of interest were (1) complications including revision surgery, infection, dislocation, impingement, and presence of a granuloma (histological diagnosis of ALVAL); (2) clinical outcomes including functional outcome, residual pain, patient activity, and patient satisfaction; and (3) radiological outcomes including loosening, presence of linear or focal osteolysis, cup migration, and stem migration.

8.2.1 Clinical Outcome Assessment Patients were evaluated at the follow-up visit using the following instruments: (a) Harris hip score (HHS), a hip-speciﬁc physician-assessed instrument [10]. (b) University of California Los Angeles (UCLA) activity scale, an outcome measure for activity assessment in THA patients, which has proven to be both reliable and valid [1, 26]. (c) Visual analogue scale (VAS) to evaluate patient satisfaction scaled between 0 (lowest satisfaction) and 10 (highest satisfaction).

8.2.2 Radiological Analysis Standardized anteroposterior pelvic and lateral radiographs made in the immediate postoperative period were compared with radiographs made during the most recent follow-up visit. The radiographs were analyzed independently by two experienced orthopedic surgeons (CB, AL) who did not participate to the follow-up evaluation. Radiological loosening was deﬁned by the criteria of Harris et al. [11] (cemented stems) and of Engh et al. [8] (uncemented stems) for the femoral component and by the criteria of Massin et al. [16] for the acetabular component. Migration of the femoral stem was measured by quantifying any change in distance between the tip of the proximal part of the femoral stem and the tip of the greater trochanter. Cup inclination was determined on anteroposterior radiographs by measuring the angle formed by the intersection of the line joining the inferior aspect of the teardrop and the line joining the highest and lowest points of the ellipse projected on the radiograph, as described by Sutherland et al. [23]. Movement of >5 mm between follow-up radiographs was taken to represent migration. Radiographs were examined for evidence of osteolysis, spot

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Fig. 8.1 X-ray of a 74-yearold patient with persisting pain 1.5 years after THA. We can observe a radiolucent line around the acetabular cup and signs of stem loosening. At revision, both the stem and cup were loose. A big amount of metallosis was found preoperatively

welds, bone condensation, and reactive lines in each of the seven femoral zones of Gruen et al. [9] and the three acetabular zones of DeLee and Charnley [7]. Heterotopic ossiﬁcation was graded using the system devised by Brooker et al. [3] (Fig. 8.1).

8.2.3 Data Collection Information about preoperative status and surgical intervention, including implant- and technique-related details, was routinely documented by the operating surgeon on speciﬁcally designed data collection forms. Preoperative, immediately postoperative, and followup radiographs were systematically collected. Information about comorbidities and in-hospital complications was routinely retrieved from the anesthesia record and the discharge summary. The treatment of any major complication or arthroplasty revision performed at our hospital or reported to the orthopedic surgeon during one of the follow-up visits was systematically included in the database. All patients were contacted by mail and/ or phone to arrange for a follow-up visit. Follow-up examinations were done by three surgeons who had not performed the operations.

8.3 Results Between September 2004 and September 2008, 89 primary THAs were performed in 80 patients with a mean age of 52 ± 12 years (range, 25–83 years). Of those 66 (74%) were men. The mean BMI was 25.8 ± 5.0. Preoperatively, the mean Harris hip score, available for 80 THAs, was 56.0 ± 15.0. A positive Trendelenburg sign was found in 31 cases (35%).

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Main diagnoses were primary osteoarthritis (OA) in 42 patients (47%), aseptic necrosis in 32 (36%), dysplasia in 8 (9%), and posttraumatic OA in 7 patients (8%). An uncemented stem was used in 70 (79%) and a cemented stem in 19 patients (21%). Forty-nine (55%) interventions were performed via a lateral transgluteal approach and 40 (45%) via a posterior approach. Mean operating time was 120 min (range, 60–210 min), and the median length of stay in hospital was 9 days (range, 5–22 days). The mean cup inclination on the postoperative radiographs was 38 ± 7° (range 14–54°). In two cases, the cup inclination was greater than 50°. Three patients developed a prosthesis infection, two within the ﬁrst month postoperative and one at 10 months postoperative (origin probably hematogenous). In two cases, the treatment was irrigation and debridement, and one prosthesis was revised. No dislocation occurred. One patient had persistent sciatic nerve palsy. Of the 89 THAs operated upon, 80 were seen at a mean follow-up of 39 months (range, 16–67 months), 4 were lost to follow-up and 5 patients refused or were unable to attend the visit. However, none of these 5 patients underwent revision. Overall, 9 THAs (9/85, 10.6%) were revised on average 30 months (range, 8–60) after the operation. The reasons for revision were aseptic loosening in four cases, presence of a granuloma (histological diagnosis of ALVAL) in three, deep infection in one, and impingement in one case. Radiographic analysis revealed linear (n = 2) and focal (n = 3) osteolysis as well as early cup migration (n = 2). In ﬁve of the revised patients, no radiographic changes were found. Fifty-ﬁve (68.8%) of the 80 patients with follow-up had an HHS between 80 and 100 points, 6 (7.5%) between 70 and 79, 11 (13.7%) between 60 and 69, and 8 (10.0%) patients had a HHS lower than 60 points. Among those who were not revised, the mean HHS improved from 55.2 to 88.4 points (mean increase 33.2 points, 95% CI 27.7; 38.7). The mean activity level (UCLA scale) at follow-up was 6.4 (±1.8). Overall, mild to severe pain was reported in 14 cases and occasional pain in 22. Groin pain was present in 18 patients (18 THAs, 22.5%), 7 of them belonged to the revised group. In 61 (76.3%) of the 80 THAs with follow-up, the results were considered as satisfying or very satisfying by the patients. Mean patient satisfaction on the VAS scale among those who were not revised was 9.0 (±1.3).

8.4 Discussion The use of LDMOM acetabular components was advocated as giving superior results with respect to implant stability. In vitro studies have supported this hypothesis [4], and lower dislocation rates were observed in vivo. Primary tribologic results of in vitro studies have lend support to the hypothesis that LDMOM bearings might improve THA longevity [21], but clinical series have shown different results [2, 13, 15]. Concern started when midterm results of different resurfacing systems were published that showed high rates of revision and a substantial number of pseudotumors [6, 18]. Nevertheless, the main adverse effect leading to revision in these patients was fracture of the femoral neck [18, 22]. Hence, surgeons continued implanting this type of acetabular component until studies showed high revision rates related to failure of the acetabular side.

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Fig. 8.2 Metallosis found around the cone of the femoral stem at revision. This was a typical finding at almost all of our revision cases

We decided to conduct this study in Geneva because some of the patients of our prospective THA registry complained of pain at follow-up. The failure rate of the acetabular component found in our series is in accordance with results of other published series [2, 13, 15, 17, 19, 20]. Published revision rates ranged from 11% to 15% with a follow-up from 2 to 5 years. One study showed a very high revision rate of 32% [20] after a mean follow-up of 2 years. This rate can be attributed to the low threshold of patient complains accepted from surgeons, before a decision for revision is taken, now that DUROM problems have been identiﬁed. In all series, the reasons for most revisions were related to the cup. The problems were the following: (1) a higher rate of cup loosening; (2) presence of metallosis, pseudotumors and high concentrations of cobalt ions during revision surgery; (3) presence of stem loosening; and (4) higher infection rates.

1. The higher rate of cup loosening can be attributed to different problems that may result from the particularity of the design of the cup (ﬂanges and over dimensioned rim), quality of porous coating, and of course, difﬁculty in achieving correct sitting of the implant. 2. As to the presence of metallosis, pseudotumors and high concentrations of cobalt ions during revision surgery, implant malpositioning with incorrect cup inclination has been incriminated to produce edge loading that could result in a high rate of particle release [12]. Nevertheless, in our study, we did not ﬁnd a correlation between implant malpositioning and presence of such complications. However, this might be due to the relatively small sample size. The presence of metallosis and pseudotumors might also be related to the use of adaptor sleeves in our series [14]. In all revised cases, we found metallosis around the stem cone and in the adaptor sleeve. This metallosis could be due to electrochemical incompatibilities arising from the use of titanium stems in conjunction with stainless steel cups. However, this remains a hypothesis, and further studies are needed to prove it (Fig. 8.2). 3. Furthermore, in our series, we had two loose stems. The reason for that could be the metallosis found preoperatively, or there could be biomechanical reasons as implied by Theodorou who showed that the use of large heads in THA could lead to incorrect

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Fig. 8.3 Acetabular cup after explantation showing no osteo-integration

distribution of forces around the metaphysis and, hence, to early stem loosening [24]. Once more, we cannot prove such a hypothesis on a small series of patients. 4. We observed three prosthesis infections in our series. The rate was superior to that of our registry [25]. A recent paper published by Daou et al. showed that in case of high cobalt concentrations, macrophages were malfunctioning [5]. This ﬁnding dictates awareness with the use of metal-on-metal couples in general (Fig. 8.3).

8.5 Conclusion According to the results from our series and from others, we believe that the use of LDMOM cups in conjunction with standard stems should be discontinued. Important problems arising from their surgical technique difﬁculty as well as from design and manufacturing particularities leading to inferior results in short- and midterm follow-up.

References 1. Beaule PE, Dorey FJ et al (2006) The value of patient activity level in the outcome of total hip arthroplasty. J Arthroplasty 21(4):547–552 2. Berton C, Girard J et al (2010) The Durom large diameter head acetabular component: early results with a large-diameter metal-on-metal bearing. J Bone Joint Surg Br 92(2):202–208 3. Brooker AF, Bowerman JW et al (1973) Ectopic ossiﬁcation following total hip replacement. Incidence and a method of classiﬁcation. J Bone Joint Surg Am 55(8):1629–1632 4. Crowninshield RD, Maloney WJ et al (2004) Biomechanics of large femoral heads: what they do and don’t do. Clin Orthop Relat Res 429:102–107

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5. Daou S, El Chemaly A et al (2011) The potential role of cobalt ions released from metal prosthesis on the inhibition of Hv1 proton channels and the decrease in Staphylococcus epidermidis killing by human neutrophils. Biomaterials 32(7):1769–1777 6. Davies AP, Willert HG et al (2005) An unusual lymphocytic perivascular inﬁltration in tissues around contemporary metal-on-metal joint replacements. J Bone Joint Surg Am 87(1):18–27 7. DeLee JG, Charnley J (1976) Radiological demarcation of cemented sockets in total hip replacement. Clin Orthop Relat Res 121:20–32 8. Engh CA, Bobyn JD et al (1987) Porous-coated hip replacement. The factors governing bone ingrowth, stress shielding, and clinical results. J Bone Joint Surg Br 69(1):45–55 9. Gruen TA, McNeice GM et al (1979) “Modes of failure” of cemented stem-type femoral components: a radiographic analysis of loosening. Clin Orthop Relat Res 141:17–27 10. Harris W (1969) Traumatic arthritis of the hip after dislocation and acetabular fractures: treatment by mold arthroplasty. An end-result study using a new method of result. J Bone Joint Surg Am 51(4):737–755 11. Harris WH, McCarthy JC, O’Neill DA (1982) Femoral component loosening using contemporary techniques of femoral cement ﬁxation. J Bone Joint Surg Am 64:1063–1067 12. Hart AJ, Buddhdev P et al (2008) Cup inclination angle of greater than 50 degrees increases whole blood concentrations of cobalt and chromium ions after metal-on-metal hip resurfacing. Hip Int 18(3):212–219 13. Illgen RL 2nd, Heiner JP et al (2010) Large-head metal-on-metal total hip arthroplasty using the Durom acetabular component at minimum 1-year interval. J Arthroplasty 25(6 Suppl): 26–30 14. Lavigne M, Belzile EL et al (2011) Comparison of whole-blood metal ion levels in four types of metal-on-metal large-diameter femoral head total hip arthroplasty: the potential inﬂuence of the adapter sleeve. J Bone Joint Surg Am 93(Suppl 2):128–136 15. Long WT, Dastane M et al (2010) Failure of the Durom Metasul acetabular component. Clin Orthop Relat Res 468(2):400–405 16. Massin P, Schmidt L et al (1989) Evaluation of cementless acetabular component migration. An experimental study. J Arthroplasty 4(3):245–251 17. Mertl P, Boughebri O et al (2010) Large diameter head metal-on-metal bearings total hip arthroplasty: preliminary results. Orthop Traumatol Surg Res 96(1):14–20 18. Morlock MM, Bishop N et al (2008) Modes of implant failure after hip resurfacing: morphological and wear analysis of 267 retrieval specimens. J Bone Joint Surg Am 90(Suppl 3):89–95 19. Naal FD, Pilz R, Munzinger U, Hersche O, Leunig M (2011) High revision rate at 5 years after hip resurfacing with the Durom implant. Clin Orthop Relat Res 469(9):2598–2604 20. Ng VY, Arnott L et al (2011) Perspectives in managing an implant recall: revision of 94 Durom Metasul acetabular components. J Bone Joint Surg Am 93(17):e100 (101–105) 21. Schmalzried TP, Peters PC et al (1996) Long-duration metal-on-metal total hip arthroplasties with low wear of the articulating surfaces. J Arthroplasty 11(3):322–331 22. Steffen RT, Foguet PR et al (2009) Femoral neck fractures after hip resurfacing. J Arthroplasty 24(4):614–619 23. Sutherland CJ, Wilde AH et al (1982) A ten-year follow-up of one hundred consecutive Muller curved-stem total hip-replacement arthroplasties. J Bone Joint Surg Am 64(7):970–982 24. Theodorou EG, Provatidis CG et al (2011) Large diameter femoral heads impose signiﬁcant alterations on the strains developed on femoral component and bone: a ﬁnite element analysis. Open Orthop J 5:229–238 25. Uckay I, Lubbeke A et al (2009) Low incidence of haematogenous seeding to total hip and knee prostheses in patients with remote infections. J Infect 59(5):337–345 26. Zahiri CA, Schmalzried TP et al (1998) Assessing activity in joint replacement patients. J Arthroplasty 13(8):890–895

Polyethylene Wear in Metal-Backed Cups: A Retrospective Analysis of 200 Uncemented Prostheses

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Walter van der Weegen, Shennah Austen, Thea Sijbesma, and Henk J. Hoekstra

9.1 Introduction Uncemented total hip prostheses were introduced some 40 years ago, after disappointing results with cemented hip prostheses in young and active patients [4, 8, 10, 56]. In orthopedic literature, research on uncemented hip prostheses has focused on the survival of the uncemented femoral stem, and in general, excellent results were reported [1, 35, 37, 42]. Although the femoral component showed excellent performance, recent in vivo studies have reported increased wear of the polyethylene (PE) liner of the uncemented acetabular cup [6, 18, 25, 32]. This PE wear results in PE particles being distributed in the tissue surrounding the prosthesis, with macrophages being activated by these particles. These activated macrophages induce osteolysis (see Fig. 9.1) which in the end results in aseptic loosening of the prosthesis [19, 27, 29, 46, 54, 60]. Although uncemented hip prostheses vary greatly in design, they all have a metalbacked acetabular cup (see Fig. 9.2). This metal-backing is needed since direct contact between bone and PE results in osteolysis [23, 29, 51]. Metal-backed cups are made more biocompatible by applying coatings which stimulate bone ingrowth. These coatings are either porous or hydroxyapatite (HA) coatings. When metal-backed cups were developed, a better force distribution with less peak forces was expected along the bone-prostheses interface. Recent studies however stated there was less stress shielding with cemented cups than with uncemented cups [14, 44]. Another possible disadvantage from metal-backed

W. van der Weegen, M.Sc. (*) Department of Orthopedic Surgery, St. Anna Hospital, Bogardeind 2, 5664 EH, Geldrop, The Netherlands e-mail: [email protected] S. Austen, M.D. Department of Orthopedic Surgery, University of Maastricht, Maastricht, The Netherlands T. Sijbesma, M.D., Ph.D. • H.J. Hoekstra, M.D. Department of Orthopedic Surgery, St. Anna Hospital, Geldrop, The Netherlands K. Knahr (ed.), Total Hip Arthroplasty, DOI 10.1007/978-3-642-27361-2_9, © 2012 EFORT

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Fig. 9.1 Osteolysis

Fig. 9.2 Metal-backed cup

cups is the dislocation or rotation of the PE liner from the metal-backing, resulting in additional wear and an increased number of released PE particles. This type of wear is known as “backside” wear [3, 31]. Increased PE wear is most likely a multifactorial process inﬂuenced by, for example, the manner in which PE is produced and sterilized, the time between production and implantation (known as “shelf life”), the inclination angle of the cup, and the activity levels of the patient. Since we had concerns on the frequency of observed wear in our patient population, we retrospectively reviewed our ﬁrst 200 uncemented hip prostheses using (Mallory-Head). The long-term survival of the femoral component of this particular prosthesis is well documented and has excellent results. Only a few studies report on acetabular wear and survival using this design. Yamamota et al. found a mean liner wear of 0.3 mm after 3 years, 0.55 mm after 5 years, and increasing to 0.7 mm after almost 7 years of follow-up [61]. Kurtz concluded that the threshold for osteolysis is a head penetration rate of >0.1 mm per

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year. He also reported that osteolysis could not be detected with a head penetration rate of <0.05 mm per year [32]. Other studies reported an osteolysis threshold at a head penetration rate of 0.1–0.2 mm per year [15, 16, 33, 53, 55]. We therefore used a head penetration rate of >0.2 mm per year to classify any case as excessive wear. The primary objective of our study was to evaluate how many of the 200 implanted prostheses showed a liner wear of more than 0.2 mm per year. The frequency of any osteolysis and implant survival was also evaluated.

9.2 Method Our ﬁrst consecutive 200 uncemented total hip prostheses (Mallory-Head), implanted between November 1997 and September 2002, were retrospectively analyzed. See Table 9.1 for patient characteristics. In all cases, an uncemented porous-coated femoral stem was used with a 28-mm ceramic head and a porous-coated ringloc acetabular cup. The liner was made of conventional ultra-high molecular weight polyethylene (UHMWPE) (ArCom®, Biomet, Warsaw), manufactured with compression molding and sterilized with gamma radiation in argon gas. Liner thickness ranged from 4.8 (cup size 48) to 11.8 mm (cup size 62). Mean shelf life was four months (range 0–41). All prostheses were implanted through the posterolateral approach. All patients were asked to return for clinical followup including a standard anteroposterior (AP) radiograph. Medical ﬁle data were collected on primary diagnosis, BMI, complications, and details of the used components. Of all patients, 89% completed a Duke Activity Index [26] to measure current activity levels. There were 36 patients lost to follow-up (37 prostheses): 9 were deceased, 16 were revised, and we were unable to contact 10 patients. This left us with 163 prostheses (81.5%) available for analysis of PE wear. Liner wear was evaluated by measuring the two-dimensional displacement of the femoral head relatively to the cup position using software (Pro 3D software, Draftware Inc. Vevay, USA). We used the most recent AP radiograph (see Fig. 9.3). To check for interobserver reliability, a sample of ten radiographs was measured by an experienced evaluator of Draftware Inc., and all PE wear measurements were 100% identical. This is possible by using edge-detection features in

Table 9.1 Patient demographics Male (n) Female (n) Age (years) BMI (kg/m2) Bilateral (n) Diagnosis: OA AVN FC

98 (49%) 102 (51%) 54.6 (range 29–69) 26.9 (range 17.6–37.5) 36 (18%) 187 (93.5%) 11 (5.5%) 2 (1%)

OA osteoarthritis, AVN avascular necrosis, FC fractured collum

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Fig. 9.3 Measurements on AP radiograph

the software, limiting the observer input on the obtained measurements. Besides the use of software, we retrospectively checked medical ﬁles if PE wear was noted by the orthopedic surgeon. We set the threshold for acceptable wear at <0.2 mm per year. A sensitivity analysis with a threshold of 0.1 mm per year was also calculated. We calculated the correlation between wear and the following subgroups: age, BMI, activity level, cup inclination angle, acetabular component size, liner thickness, and shelf life. Differences in wear between male and female patients were tested using an unpaired Student’s t-test. Implant survival was calculated using the Kaplan-Meier (KM) method. All statistics were performed using SPSS software (SPSS Statistics, version 17.0, IBM Corporation, Somers, USA). The most recent AP radiograph was screened for any radiolucencies or osteolysis according to the zones described by DeLee and Charnley for the acetabular component and the zones described by Gruen for the femoral component. [13, 24]

9.3 Results 9.3.1 Wear and Osteolysis The mean-measured PE wear was 0.2 mm per year (range 0.07–0.5), after a mean follow-up of 8.3 years. In 53.4% of all cases, the PE wear was ³0.2 mm per year (see Fig. 9.4), and if

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Polyethylene Wear in Metal-Backed Cups: A Retrospective Analysis of 200 Uncemented Prostheses

Fig. 9.4 Boxplot of wear rate per year

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0.50

Wear (mm/year)

0.40

0.30

0.20

0.10

0.00

Table 9.2 Subanalyses of PE wear Age BMI Activity level Acetabular inclination Shell size Shelf life

Correlation −0.4 0.056 0.166 0.236 0.156 0.065

p value 0.61 0.48 0.053 0.002 0.046 0.41

the threshold for acceptable wear was set at 0.1 mm per year, 96.3% of all liners showed excessive PE wear. There was a signiﬁcant correlation between PE wear and cup inclination angle and between PE wear and component size, see Table 9.2. Mean PE wear was signiﬁcantly higher in male patients than in female patients (respectively, 0.22 mm per year versus 0.19 mm per year, p = 0.02). On average, 24.3% of the original liner thickness was lost to PE wear (range 10.7–42.7%). In 41 cases, PE wear was observed during routine clinical follow-up and noted in the medical ﬁle (24.8%), with a mean of 93 months after index surgery (range 40–120). Osteolysis was observed in ﬁve cases (see Table 9.3). The measured PE wear in these ﬁve patients had a mean of 0.22 mm per year (range 0.19–0.26).

9.4 Implant Failure Of the 200 prostheses, 16 were revised, and one was scheduled for revision. Most frequent reason for revision was PE liner wear (N = 10), see Tables 9.4 and 9.5. Of the ten patients revised for liner wear, a straightforward cup exchange was done in nine cases. In two cases, the liner was detached from the metal-backing, and in one of these two cases, metallosis was observed. In the other case, a ﬁbrous tissue layer was observed between the PE

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Table 9.3 Osteolysis Osteolysis Femoral component – None – Gruen zone 1 or 7 – Gruen zone 2–6 Acetabular component – None – DeLee and Charnley zone 1 – DeLee and Charnley zone 2 – DeLee and Charnley zone 3

N

%

160 3 0

98.2 1.8 0

158 2 2 1

96.9 1.2 1.2 0.6

Table 9.4 Overview of revision cases Reason for revision Aseptic loosening Liner exchange Dislocation Wound infection Breakage ceramic head Total

N (%) 1 (0.5) 9 (4.5) 4 (2) 1 (0.5) 1 (0.5) 16 (8)

Table 9.5 Wear-related revision Casus 1 2 3 4 5 6 7 8 9 10

Months to revision 77 104 107 107 109 109 110 144 Unknown Planned

Details Liner exchange, components well ﬁxed Liner exchange, components well ﬁxed Liner exchange, components well ﬁxed Liner exchange, components well ﬁxed Liner exchange, components well ﬁxed Liner exchange, components well ﬁxed Liner exchange, components well ﬁxed Aseptic cup loosening Revised in other hospital, patient deceased Wear observed

liner and the metal-backing. Four cases needed bone impaction grafting for an acetabular cyst. Mean time to revision was 108 months (range 77–144), and the mean observed wear in the revised patients was 0.28 mm per year (range 0.21–0.45). The KM probability estimate of survival, with revision for any reason as end point, was 90.7% after 12 years of follow-up (95% – BI: 85.6–94.2). With only revision cases due to wear as end point, the KM survival estimate was 93.1% after 12 years follow-up (95% – BI: 79.9–100), see Fig. 9.5.

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Fig. 9.5 Kaplan-Meier survival probability estimate

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100 90 80

Cum Survival (%)

70

Revision wear Revision any reason

60 50 40 30 20 10 0.0 0

1

2

3

4

5

6 7 8 Time (y)

9 10 11 12 13 14

9.5 Discussion In our study, we report a high proportion (53.4%) of UHMWPE liners with an wear rate of ³0.2 mm per year, after a mean follow-up of 8.3 years. In contrast, implant survival after 12 years is acceptable (KM 90.1%). However, it is disturbing that in literature the liner wear rate is reported to be nonlinear, with an increase in PE wear 7–8 years after index surgery [26, 61]. These ﬁndings suggest that we have to expect an increasing number of revisions within the next few years of follow-up. Parvizi conducted a study with longer mean followup than our study and found a revision rate of 20% after 11 years of follow-up [47]. And McLaughlin reported a revision rate of 65% after 16 years [41]. A possible explanation for the measured amount of wear can be found in the type of PE used. Free radicals, formed during the sterilization process, negatively inﬂuence the characteristics of conventional UHMWPE. Before and after implantation, these free radicals react to oxygen. This oxidation leads to accelerated wear rates. Oxidation can be reduced by using highly cross-linked polyethylene (HXLPE). Compared to conventional PE, HXLPE shows a signiﬁcant reduction of the head penetration rate in several clinical studies [30, 40, 43, 50]. Currently, we do not know if in the long term, free radicals are released from HXLPE and can still cause oxidation. A recent method to prevent this happening is the infusion of vitamin E into (highly cross-linked) PE to scavenger any free radicals. This method is too new for clinical studies to be available. Alternatively, other bearing materials may be used such as metal or ceramics.

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Although there are some beneﬁts of metal-on-metal (MoM) bearings such as low dislocation rates (due to the large diameter) and very low wear rates reported in in vitro studies [2, 9, 11, 21], these beneﬁts are outweighed by the occurrence of serious complications due to an adverse reaction to metal debris (ARMD), as reported in recent clinical studies [12, 34, 36]. In general, recent clinical studies using MoM bearings report higher revision rates than expected with the introduction of these bearings [49]. Clinical studies with ceramic bearings have good long-term results, but the use of ceramics is limited by high cost, “squeaking,” and difﬁcult revision after liner fractures ([7, 45, 48, 39, 58, 59]). The choice of material for the femoral head does not inﬂuence the PE wear rate signiﬁcantly; only small differences in liner wear were observed between different materials for the femoral head [57]. Wear is not only dependent on the used materials but indeed multifactorial. In our study cohort, more wear was observed in cups with a steeper inclination angle and in male patients. This corresponds with earlier publications [5, 20, 61]. In contrast to earlier studies, we observed more wear with larger sizes of acetabular cups. We could not identify any possible explanation for this observation. We explored the hypothesis that larger cups would be more difﬁcult to place, resulting in steeper cup placement. However, there was no signiﬁcant difference in cup inclination angle between smaller (54 mm) and larger (³56 mm) cup sizes. From our analysis on different subgroups, we could not detect any relation between age, BMI, shelf life or activity level, and the measured PE wear in our study cohort. This was unlike ﬁndings from other studies [5, 52, 61]. There is however a large heterogeneity in number and characteristics of the included patients, making it difﬁcult to compare these results. In our study, shelf life was quite short with an average of 4 months. The measured wear in all patients revised because of liner wear was more than 0.2 mm per year. However, 82.5% of all our patients with a PE wear rate of >0.2 mm per year had no radiolucent zones, no cyst formation, or such clinical symptoms that revision surgery was indicated. This might be due to the genetic proﬁle of these patients, which makes them resistant to osteolysis [19, 23]. The observed wear in our study is comparable to other studies using metal-backed cups [17, 22, 28, 38]. Considering this comparable high wear rate, the number of cases with aseptic loosening (0.5%) and the number of observed osteolysis (5.5%) in our series is low in comparison to other studies. Although, most of these other studies had longer follow-up than our series. For example, Emms et al. found a 17.1% osteolysis rate and a wear-related revision percentage of 20% after 11.5 years of follow-up [18]. The fact that we only used the most recent radiograph for PE wear evaluation, might explain we only observed osteolysis instead of any radiolucency. It is also striking that the number of cases with aseptic loosening in our study cohort is very low. This might either be because we revised patients early or by the retrospective nature of our study which makes it more difﬁcult to classify aseptic loosening. Another explanation might be that the osteointegration of the coating is so effective, that the acetabular component appears to be well ﬁxed in place during revision surgery, even if only a small area is integrated into the bone tissue. The optimal treatment if wear is observed and the best timing to perform revision surgery are clinical issues described in a treatment algorithm by Goosen et al. [22], see Fig. 9.6.

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Polyethylene Wear in Metal-Backed Cups: A Retrospective Analysis of 200 Uncemented Prostheses

Primary uncemented metal backed acetabular component

Standard roentgenographic analysis

Cavitary osteolysis/ evident PE-wean acetabular component associated with a high wear rate

Segmental osteolysis

Helical CT scan

Exploration prosthesis: judgement of shell

Minimal or no osteolytic lesions

Repeat hellical CT scan yearly and consider biphosphonates

(Progression to) considerable cavitary or segmental asteolysis

Stable: Debridement/ bone grafting/ replace liner

Unstable: Remove shell/ debridement/ bone grafting/ replace shell and liner

Determine amount of bone grafts at hemisphere contacting with acetabular component

<50%: Uncemented acetabular component

<50%: Cemented acetabular component

Fig. 9.6 Treatment algorithm for uncemented metal-backed acetabular components by Goosen et al. (reprinted with permission, [22])

Strong points of our study are the large number of included prostheses, the use of a validated method to measure wear, and the analyses of multiple variables which might inﬂuence wear. Our study is limited by the retrospective design, the lack of a control group, the loss to follow-up, and the limited duration of the follow-up. Based on our results and the current literature, we strongly question the use of conventional UHMWPE in uncemented total hip prostheses with metal-backed cups. Detailed follow-up,

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especially in the long term, can prevent serious complications due to the use of conventional PE. Studies with longer follow-up, preferably more than 10 years, are necessary to validate the safety of conventional UHMWPE in uncemented total hip prostheses.

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38. Martell JM, Verner JJ, Incavo SJ (2003) Clinical performance of a highly cross-linked polyethylene at two years in total hip arthroplasty: a randomized prospective trial. J Arthroplasty 18(7 Suppl 1):55–59 39. Matar WY, Restrepo C (2010) Revision Hip arthroplasty for ceramic-on-ceramic squeaking hips does not compromise the results. J Arthroplasty 25(6):81–86 40. McCalden RW, MacDonald SJ, Rorabeck CH et al (2009) Wear rate of highly cross-linked polyethylene in total hip arthroplasty. A randomized controlled trial. J Bone Joint Surg Am 91(4):773–782 41. McLaughlin JR, Lee KR (2010) Total Hip arthroplasty with an uncemented tapered femoral component in patients younger than 50 years. J Arthroplasty 26(1):9–15 42. Merle C, Clarius M, Aldinger PR (2010) Long-term results of uncemented stems in total hip arthroplasty: analysis of survival rates with a minimum 15-year follow-up. Orthopade 39(1):80–86 43. Mu Z, Tian J, Wu T, Yang J, Pei F (2009) A systematic review of radiological outcomes of highly cross-linked polyethylene versus conventional polyethylene in total hip arthroplasty. Int Orthop 33(3):599–604 44. Mueller LA, Schmidt R, Ehrmann C et al (2009) Modes of periacetabular load transfer to cortical and cancellous bone after cemented versus uncemented total hip arthroplasty: a prospective study using computed tomography-assisted osteodensitometry. J Orthop Res 27(2): 176–182 45. Murphy SB, Ecker TM, Tannast M (2006) Two- to 9-year clinical results of alumina ceramicon-ceramic THA. Clin Orthop Relat Res 453:97–102 46. Orishimo KF, Claus AM, Sychterz CJ, Engh CA (2003) Wear and osteolysis in hips with coated cementless cup after seven years of follow-up. J Bone Joint Surg Am 85-A(6): 1095–1099 47. Parvizi J, Keisu KS, Hozack WJ, Sharkey PF, Rothman RH, Petsatodis GE, Papadopoulos PP, Papavasiliou KA et al (2010) Primary cementless total hip arthroplasty with an alumina ceramic-on-ceramic bearing. J Bone Joint Surg Am 92:639–644 48. Petsatodis GE, Papadopoulos PP, Papavasiliou KA, Hatzokos IG, Agathangelidis FG, Christodoulou AG (2010) Primary cementless total hip arthroplasty with an alumina ceramicon-ceramic bearing: results after a minimum of twenty years of follow-up. J Bone Joint Surg Am 92(3):639–644 49. Prosser GH, Yates PJ, Wood DJ et al (2010) Outcome of primary resurfacing hip replacement: evaluation of risk factors for early revision 12,093 replacements from the Australian joint registry. Clin Orthop 81(1):66–71 50. Rajadhyaksha AD, Brotea C, Cheung Y et al (2009) Five-year comparative study of highly cross-linked (crossﬁre) and traditional polyethylene. J Arthroplasty 24(2):161–167 51. Ren P-G, Irani A, Huang Z et al (2010) Continuous infusion of UHMWPE particles induces increased bone macrophages and osteolysis. Clin Orthop Relat Res 469(1):113–122 52. Röder C, Bach B, Berry DJ et al (2010) Case–control study of 4420 patients obesity, age, sex, diagnosis, and ﬁxation mode differently affect early cup failure in total hip arthroplasty. J Bone Joint Surg Am 92:1954–1963 53. Schewelov TV, Sanzén L, Börlin N, Markusson P, Önsten I (2004) Accuracy of radiographic and radiostereometric wear measurement of different hip prostheses an experimental study. Acta Orthop Scand 75(6):691–700 54. Shen Z, Crotti TN, McHugh KP, Matsuzaki K, Gravallese EM, Bierbaum BE, Goldring SR (2006) The role played by cell-substrate interactions in the pathogenesis of osteoclastmediated peri-implant osteolysis. Arthritis Res Ther 8(3):R70 55. Sochart DH (1999) Relationship of acetabular wear to osteolysis and loosening in total hip arthroplasty. Clin Orthop Relat Res 363:135–150

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56. Stauffer R (1982) Ten-year follow-up study of total hip replacement 1107. J Bone Joint Surg Am 64:983–990 57. Stilling M, Nielsen KA, Søballe K, Rahbek O (2009) Clinical comparison of polyethylene wear with zirconia or cobalt-chromium femoral heads. Clin Orthop Relat Res 467(10): 2644–2650 58. Swanson TV, Peterson DJ, Seethala R, Bliss RL, Spellmon CA (2010) Inﬂuence of prosthetic design on squeaking after total hip arthroplasty. J Arthroplasty 25(6):36–42 59. Walter WL, Yeung E, Esposito C (2010) A review of squeaking hips. J Am Acad Orthop Surg 18(6):319–326 60. Wilkinson JM, Hamer AJ, Stockley I, Eastell R (2005) Polyethylene wear rate and osteolysis: critical threshold versus continuous dose – response relationship. J Orthop Res 23:520–525 61. Yamamoto K, Imakiire A, Shishido T et al (2003) Cementless total hip arthroplasty using porous-coated Biomet acetabular cups (hexloc and ringloc types). J Orthop Sci 8(5):657–663

Immunological Adverse Reaction Associated with Low Carbide Content Metal-on-Metal Bearings in a Contemporary Cementless Total Hip Arthroplasty

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Panagiotis Korovessis, Thomas Repantis, Panagiotis Aroukatos, and Maria Repanti

10.1 Introduction Contemporary MoM THAs were introduced about 20 years ago to reduce polyethylene wear-related osteolysis and subsequent aseptic loosening. Subsequently, there have been evidence of increased metal serum levels in patients with THAs with Metasul [2, 9] and Sikomet [13] bearings. Recent histological evidence in retrievals supported the hypothesis of a delayed-type hypersensitivity reaction to CoCr debris in patients with MoM THAs with Metasul bearings [3, 18, 24]. Most studies involved THAs with high-carbide-content bearing, and only two studies reported a hypersensitivity reaction with Sikomet bearing [11, 15]. With the hypothesis that the cause of periprosthetic osteolysis in THAs with Sikomet bearing should be a delayed-type hypersensitivity, we planned a comparative controlled histological and immunocytochemical study. The aim of this study was to show signiﬁcant differences in the inﬂammatory inﬁltrate in periprosthetic retrievals from revised cementless THA with Sikomet articulation versus ceramic-on-polyethylene articulation and primary hip capsule.

P. Korovessis, M.D., Ph.D. • T. Repantis, M.D., Ph.D. (*) Department of Orthopaedics, General Hospital “Agios Andreas”, Patras, Greece e-mail: [email protected] P. Aroukatos, M.D. • M. Repanti, M.D., Ph.D. Department of Pathology, General Hospital “Agios Andreas”, Patras, Greece K. Knahr (ed.), Total Hip Arthroplasty, DOI 10.1007/978-3-642-27361-2_10, © 2012 EFORT

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10.2 Patients and Methods We compared two-matched groups of patients (MoM and CP) who had received a Zweymüller-Plus THA with two different bearing surfaces (ceramic-on-polyethylene [CP] vs. metal-on-metal [MoM]). These hips were revised for aseptic loosening and periprosthetic linear and focal osteolysis. The indications for primary THA implantation were primary osteoarthritis and secondary osteoarthritis due to developmental hip disease. Patients with history of inﬂammatory disease and pyogenic infection were excluded. Routine BSR and ESR and CRP were made in all patients of both groups to disclose infection, while tissue retrievals and primary joint capsule were routinely sent for cultures. The MoM group included 20 patients (6 men, 14 women) with 20 THAs, with a mean age ± SD of 62.5 ± 10 years, (range 42–80 years), who were revised 4.55 ± 1.7 years, (range 3–7 years) after primary implantation of a THA with Sikomet™ (Smith & Nephew Orthopaedics AG, 5000 Aarau, Switzerland) MoM (CoCr) articulation (28-mm ball head). Skin-patch test containing CoCr alloy was performed postoperatively in all patients of MoM group, but only one patient (5%) showed hypersensitivity to skin-patch test. The patients of group CP (control group I), who were operated in the same period with their counterparts of group MoM, have been subsequently selected to match some characteristics of MoM group (diagnosis, age and time lapsed from primary implantation). Age of the patients and time lapsed between primary implantation and revision surgery were similar in the two groups [MoM and CP]. CP group (control) enrolled 13 patients (7 men and 6 women) with 13 unilateral THAs, with an average age ± SD of 61 ± 9 years, (range 39–74 years), who were revised 4.8 ± 3.4 years, (range 1–13 years) following primary implantation for aseptic loss of biological ﬁxation of THA components with ceramic-on-polyethylene articulation (28-mm ball head). The acetabular component was the cementless Bicon-Plus (Smith & Nephew Orthopaedics AG, 5000 Aarau, Switzerland) cup. An RCH-1000 Chirulen ultra-high molecular weight polyethylene liner is interposed between the shell and the Sikomet SM21 Co-28Cr-6Mo low-carbon-alloy-articulating surface (ASTM F799 and 1537, ISO 583212). A 28-mm-diameter metal femoral head manufactured from Sikomet SM21 was used in all patients. Sikomet SM21 is a low-carbon, forged, vacuum-melted Co-28Cr-6Mo alloy exhibiting ﬁne-grain structure with an almost carbide-free surface. The 28-mm ceramic femoral head that was implanted in the hips of CP group was made from alumina (Ceram Tec, Plochingen, Germany). The polyethylene-articulating inlay was machined from bar-stock ultra-high molecular weight polyethylene moulded forms (ISO 5834-2:2006). Immunocytochemical analysis was made in the excised hip capsule from 13 and 7 hips of group MoM and CP, respectively, in primary implantation (controls) as well as in the newly formed capsule and periprosthetic tissues (interface membranes acetabulum Bicon- and SL-Plus stem femur) derived from 20 and 13 hips of group MoM and CP, respectively, in revision surgery. The tissue samples were ﬁxed in 10% neutral-buffered formalin and examined by light microscopy (hematoxylin-eosin, PAS, van Gieson and Pearl’s stain).

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Table 10.1 Grading of metal particles, giant cells and neutrophils Grade Metal particles

1+ Slate-blue histiocytes

Giant cells Neutrophils

£1/HPF £5/HPF Modiﬁed Mirra classiﬁcation HPF high-power ﬁeld (×400)

2+ Dusty-black histiocytes 2–4/HPF 6–49/HPF

3+ Jet-black histiocytes ³5/HPF ³50/HPF

Table 10.2 Grading of lymphocytic inﬁltration Grade Lymphocytic inﬁltration HPF high-power ﬁeld (×400)

– £5/HPF

1+ 6–20/HPF

2+ 21–50/HPF

3+ >50/HPF

Immunocytochemical analysis was performed using the ChemMate™ Dako EnVision™ Detection System HRP/DAB (Dako, Glostrup, Denmark) and included markers of T- and B lymphocytes, T-suppressor and T-helper cells, plasma cells, natural killer (NK) cells as well as macrophages and Langerhans cells. Appropriate positive and negative controls were used for each antibody. The amount of metal (CoCr)-debris-containing macrophages, number of giant cells and neutrophilic inﬁltration were estimated and graded according to the modiﬁed Mirra classiﬁcation [4, 22] (Table 10.1). Lymphocytic inﬁltration was graded by counting perivascular and diffuse-inﬁltrating lymphocytes per high-power ﬁeld (HPF, 400×) (Table 10.2). The degree of immunoreactivity for all antibodies was scored semi-quantitatively, taking into account the percentage of positive cells (i.e. weak (1+), moderate (2+) and strong (3+) for <5%, 6–49% and >50% positive cells, respectively). Differences in the number of metal particles, neutrophilic inﬁltration as well as CD68+ macrophages between independent groups (MoM vs. CP) were evaluated with the Mann– Whitney test. Differences between related groups were tested with the Wilcoxon sign test. p values <0.05 were considered as statistical signiﬁcant. Statistical analysis was performed with SPSS (version 12 for Windows).

10.3 Results The ﬁndings are summarized in the Tables 10.3 and 10.4 and Figs. 10.1, 10.2, 10.3, and 10.4. Retrievals of both groups showed similar amounts of metal particles, neutrophils and CD68+ macrophages. Within the periprosthetic tissues of MoM were detected signiﬁcantly (p < 0.001) more lymphocytes than in group CP.

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Table 10.3 Antibodies used in immunohistochemical evaluation of tissue samples Antibody CD2O CD3

Marker B-lymphocytes T-lymphocytes

CD4 CD8 CD138

T-helper cells T-suppressor cells Plasma cells

CD57 CD68 (PGM1) CD1a

Natural killer (NK) cells Histiocytes Langerhans cells

Source Biogenex, San Ramon, USA Novocastra, Newcastle upon Tyne, UK Lab Vision, Fremont CA, USA Dako, Glostrup, Denmark Novocastra, Newcastle upon Tyne, UK Dako, Glostrup, Denmark Lab Vision, Fremont CA, USA Novocastra, Newcastle upon Tyne, UK

More neutrophils (p = 0.023), lymphocytes (p = 0.013) and CD68+ macrophages (p = 0.008) were found within the periprosthetic tissues than in the primary capsule of group MoM. More T-cells than B-cells, particularly CD8+ (suppressor), were detected in group MoM periprosthetic tissues. More CD68+ macrophages were shown in the periprosthetic tissues of CP than in the capsule of control CP group (p = 0.001). Similar histological and immunocytochemical parameter values were shown within the primary capsules of both control groups. Natural killer cells (CD57+) were rare and Langerhans cells (CD1a+) were not identiﬁed in all four groups of MoM and CP (Tables 10.3 and 10.4).

10.4 Discussion Patient’s predisposition to metal hypersensitivity is currently considered as a possible explanation for periprosthetic osteolysis and failure in some contemporary THAs with MoM bearings [3, 8, 11, 15, 18, 23, 24]. However, whether the predisposition to CoCr sensitivity is a cause for periprosthetic osteolysis and subsequent loosening of contemporary THAs or a consequence of the interaction between metal debris and periprosthetic tissue remains still obscure. Although there are several reports [4, 18, 22–25] on highcarbide-content-related immunologic reaction, there is only one comparative study derived from our institutions, with selected matched controls investigating the speciﬁc immunologic reaction to low-carbide-content Sikomet by means of histological and immunocytochemical techniques [1]. The most remarkable histological ﬁndings in the retrievals from the revised metal-onmetal hips with low-carbide content, which clearly differentiate them from those shown in ceramic-on-polyethylene bearing, were: (1) extensive necrosis in all MoM hips and ﬁbrin exudation in the newly formed hip capsule, (2) diffuse and perivascular lymphocytic

Metal particlesb 1+ 5/20 (25%) 2+ 12/20 (60%) 3+ 3/20 (15%) mean ± SD 1.90 ± 0.641 Giant cellsb 1+ 20/20 (100%) 2+ 0/20 (0%) 3+ 0/20 (0%) mean ± SD 1±0 Neutrophilsb 1+ 12/20 (60%) 2+ 5/20 (25%) 3+ 3/20 (15%) mean ± SD 1.55 ± 0.76 Lymphocytic inﬁltrationc 0 0/20 (0%) 1 4/20 (20%) 2 4/20 (20%) 3 12/20 (60%) mean ± SD 2.40 ± 0.82

MoM revision 0/13 (0%) 0/13(0%) 0/13(0%) 0±0 0/13 (0%) 0/13 (0%) 0/13 (0%) 0±0 13/13 (100%) 0/13 (0%) 0/13 (0%) 1±0 6/13 (46.2%) 6/13(46.2%) 0/13 (0%) 1/13 (7.7%) 0.69 ± 0.85

7/13 (53.8%) 2/13 (15.4%) 4/13(30.8%) 1.77 ± 0.93

12/13 (92.3%) 1/13 (7.7%) 0/13 (0%) 1.08 ± 0.28

3/13 (23.1%) 8/13 (61.5%) 2/13 (15.4%) 0/13 (0%) 0.92 ± 0.64

MoM control

5/13 (38.5%) 6/13 (46.2%) 2/13 (15.4%) 1.77 ± 0.72

CP revision

4/7 (57.1%) 3/7 (42.9%) 0/7 (0%) 0/7 (0%) 0.43 ± 0.53

7/7 (100%) 0/7 (0%) 0/7 (0%) 1±0

0/7 (0%) 0/7 (0%) 0/7 (0%) 0±0

0/7 (0%) 0/7 (0%) 0/7 (0%) 0±0

CP control

<0.001

>0.05

0.001

p valuea MoM vs. CP revision >0.05

0.013

0.023

–

MoM revision vs. control –

Table 10.4 Histological and immunocytochemical ﬁndings in metal-on-metal and ceramic-on-polyethylene revision and control groups

>0.05

>0.05

–

(continued)

CP revision vs. control –

10 Immunological Adverse Reaction Associated with MoM bearings 117

MoM revision

CP revision

MoM control

CP control

p valuea MoM vs. CP revision >0.05

MoM revision vs. control 0.008

CP revision vs. control 0.001

10

CD68+ macrophagesc 1 2/20 (10%) 1/13 (7.7%) 9/13 (69.2%) 7/7 (100%) 2 4/20 (20%) 5/13 (38.5%) 4/13 (30.8%) 0/7 (0%) 3 14/20 (70%) 7/13 (53.8%) 0/13 (0%) 0/7 (0%) mean ± SD 2.60 ± 0.68 2.46 ± 0.66 1.3 ± 0.48 1±0 – – – Necrosis Yes 18/20 (90%) 0/13 (0%) 0/13 (0%) 0/7 (0%) No 2/20 (10%) 13/13 (100%) 13/13 (100%) 7/7 (100%) – – – Fibrin exudation Yes 2/20 (10%) 0/13 (0%) 0/13 (0%) 0/7 (0%) No 18/20 (90%) 13/13 (100%) 13/13 (100%) 7/7 (100%) – – – T-cells/B-cells ratio (CD3+/CD20+) T-cells > B-cells 13/20 (65%) 12/13 (92%)a 6/13 (46%) 4/7 (57%) B-cells > T-cells 7/20 (35%) 1/13 (8%)a 7/13 (54%) 3/7 (43%) Wilcoxon sign or Mann–Whitney test. p value <0.005 was considered statistical signiﬁcant MoM metal-on-metal THA, CP ceramic-on-polyethylene THA a Due to the extremely sparse lymphocytic inﬁltration observed in the CP retrievals, statistical analysis for T-, B-cells between CP and MoM groups would be impossible b Scoring was performed according to modiﬁed Mirra classiﬁcation c Scoring was performed as described in patients and methods

Table 10.4 (continued)

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Fig. 10.1 Extensive necrosis in the synovial membrane in association with Grade 3+ lymphocytic inﬁltration of the neo-capsule from a revised MoM THA is shown (stain, hematoxylin and eosin; original magniﬁcation, ×200)

Fig. 10.2 Grade 3+ diffuse and perivascular lymphocytic inﬁltration of the neo-capsule from a revised MoM THA is shown (stain, hematoxylin and eosin; original magniﬁcation, ×400)

inﬁltration and neutrophilic inﬁltration of a higher degree than in the hips of CP group and (3) much more T-cells than B-cells in the hips of CP group. However, there were some limitations in this study: (1) its retrospective character; (2) small number of revised hips and controls; (3) inconsistency in history of previous contact to CoCr before THA implantation and (4) lack of skin-patch test before primary implantation. What strengthens this study, compared with a previous study on Sikomet bearing [15], is the careful selection of the CP control group to match in age and time interval between primary implantation and revision surgery, while as controls served most of the same patients of groups MoM and CP who had received the primary THA. In contrary, others [15] used two independent groups of patients who received different non-comparable types of implants, while their control THAs were revised 14–21 years following primary implantation [15], in contrast to the Sikomet hips which were revised just 5 years following primary implantation. Furthermore, no control samples from the same hips were taken to be used as controls – as we did – during primary implantation [15].

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Fig. 10.3 (a–b) An excess of (a) T-lymphocytes (CD3+) over (b) B-lymphocytes (CD20+) at the acetabulumcup interface from a revised MoM THA is shown (stain, EnVision™, HRP/DAB; original magniﬁcation, ×400)

P. Korovessis et al.

a

b

The results of this study justiﬁed previously reported relative data [14, 15], which supported the hypothesis that a link should exist between metal debris and a speciﬁc immunological reaction probably similar to type-IV-delayed hypersensitivity [24]. However, by comparing our results with previous published data, the development of hypersensitivity reaction cannot be explained by the difference in carbon content as it was shown in retrievals from both Metasul high-carbon content [24] and Sikomet lowcarbide-content bearings [15]. The authors of a previous study [15] used similar conventional histological methods in specimens from revised Zweymüller-Plus THAs with Sikomet bearings and observed a hypersensitivity-like reaction with diffuse and perivascular inﬁltration of lymphocytes in periprosthetic tissues of 13 (76%) patients. This study justiﬁed these ﬁndings in a more detailed study with a much stronger lymphocyte inﬁltration in all 20 specimens. Milosev et al. observed polyethylene particles in 5/17 revised metal-on-metal hips [15], ﬁnding that was not justiﬁed in our MoM group, although the same cup with ultra-high molecular weight polyethylene liner, interposed between the shell and the Sikomet, was also used. The latter should be due to a probably more destruction degree at the index revision of Bicon cups in the Milosev’s [15] series.

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Fig. 10.4 (a) T-suppressor (CD8+) and (b) T-helper (CD4+) lymphocytes at the neo-capsule from a revised MoM THA are shown (stain, EnVision™, HRP/DAB; original magniﬁcation, ×400)

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a

b

In the Milosev’s series, a foreign-body reaction (Willert grades +1 to +4) to Sikomet wear particles was shown in all revised MoM hips [15]. This was justiﬁed in our MoM group with a clear evidence of ingested metal debris in all 20 hips (modiﬁed Mirra grades +1 to +3). The characteristic ﬁnding of necrosis in the newly formed capsule in 90% of the revised hips of our MoM group was not in accordance with a previous series [15] with the Sikomet articulation. Necrosis in the synovial membrane of the newly formed capsule derived from aseptically loosened THAs with same or different metal-on-metal articulations has been reported [11, 15, 21, 25]. The latter was considered by others [14] in different metal-onmetal articulation as an active inﬂammatory process. In contrast to Milosev, who reported [15] extensive (70%) presence of ﬁbrin exudation in the neo-capsule of revised hips with Sikomet articulation, we showed only a 10% ﬁbrin exudation in the hips of MoM group. Differences in the degree of Bicon loosening and component wear as well variable types of stem designs may be the cause for these differences. Park et al. [18] reported on a perivascular accumulation of CD3-positive T-cells and CD68-positive macrophages in periprosthetic tissues collected during revision surgery of

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a THA with different metal-on-metal bearing. In our study, immunocytochemistry analysis revealed the prevalence of CD8+ T-cells against CD4+ T-cells in the lymphocytic population. The prevalence of CD8+ T-cells against CD4+ T-cells in the lymphocytic population is in accordance to the theory of delayed-type hypersensitivity (DTH) as it has recently been shown that both CD4+ and CD8+ T-cells can mediate DTH [7, 10, 12, 16, 19]. Metal-on-metal bearings alloy metals (CoCr) in contemporary THAs are metal sensitizers in humans [6, 20] and in a selected population could be immunogenic in contrast to ceramic-on-polyethylene bearings where polyethylene ﬁbres elicit a foreign-body giantcell reaction [5, 6, 14, 17]. In our study, the increased incidence of T-lymphocytes in the periprosthetic retrievals in THAs with Sikomet articulation in contrast to ceramic-on-polyethylene bearings could be considered to be consistent with a delayed-type hypersensitivity (DTH) reaction. Since there were inconsistent data regarding previous contacts with Cr and Co ions (dental bridges, osteosynthesis material containing CO, Cr, etc.) neither was investigated any genetic predisposition in our patients, who received THA with metal-onmetal articulation, we hypothesized that the ﬁrst sensitization of T-lymphocytes derived from continuous contact with MoM-CoCr-released metal debris. Prospective randomized studies with preoperative patch tests and eventually genetic control before implantation of a THA with Sikomet bearing would be of importance for the aetiology of delayed-type hypersensitivity (DTH) reaction. However, as far as we know, Sikomet bearing is not more in use, and thus such a study would be unethical.

References 1. Aroukatos P, Repanti M, Repantis T, Bravou V, Korovessis P (2010) Immunologic adverse reaction associated with low-carbide metal-on-metal bearings in total hip arthroplasty. Clin Orthop Relat Res 468(8):2135–2142 2. Brodner W, Bitzan P, Meisinger V, Kaider A, Gottsauner-Wolf F, Kotz R (2003) Serum cobalt levels after metal-on-metal total hip arthroplasty. J Bone Joint Surg Am 85:2168–2173 3. Davies AP, Willert HG, Campbell PA, Learmonth ID, Case CP (2005) An unusual lymphocytic perivascular inﬁltration in tissues around contemporary metal-on-metal joint replacements. J Bone Joint Surg Am 87:18–27 4. Doorn PF, Mirra JM, Campbell PA, Amstutz HC (1996) Tissue reaction to metal on metal total hip prostheses. Clin Orthop 329(Suppl):S187–S205 5. Green TR, Fisher J, Stone M, Wroblewski BM, Ingham E (1998) Polyethylene particles of a critical size are necessary for the induction of cytokines by macrophages in vitro. Biomaterials 19:297–302 6. Hallab N, Merritt K, Jacobs JJ (2001) Metal sensitivity in patients with orthopedic implants. J Bone Joint Surg Am 83:428–436 7. Hallab NJ, Caicedo M, Finnegan A, Jacobs JJ (2008) Th1 type lymphocyte reactivity to metals in patients with total hip arthroplasty. J Orthop Surg 13:6 8. Jacobs JJ, Hallab NJ (2006) Loosening and osteolysis associated with metal-on-metal bearings: a local effect of metal hypersensitivity? J Bone Joint Surg Am 88:1171–1172 9. Jacobs JJ, Skipor AK, Doorn PF, Campbell P, Schmalzried TP, Black J, Amstutz HC (1996) Cobalt and chromium concentrations in patients with metal on metal total hip replacements. Clin Orthop Relat Res 329(Suppl):S256–S263

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10. Kalish R, Askenase PH (1999) Molecular mechanisms of CD8+ T cell-mediated delayed hypersensitivity: implications for allergies, asthma, and autoimmunity. J Allergy Clin Immunol 103:192–199 11. Korovessis P, Petsinis G, Repanti M, Repantis T (2006) Metallosis after contemporary metalon-metal total hip arthroplasty. Five to nine-year follow-up. J Bone Joint Surg Am 88:1183–1191 12. Kumar V, Cotran RS, Robbins SL (1997) Basic pathology. W.B. Saunders Co, Philadelphia, pp 94–96 13. Lhotka C, Szekeres T, Steffan I, Zhuber K, Zweymuller K (2003) Four-year study of cobalt and chromium blood levels in patients managed with two different metal on metal total hip replacements. J Orthop Res 21:189–195 14. Lintner F, Bohm G, Huber M, Zweymuller K (2003) Synovial tissue following revision total hip replacement with metal-on-metal joints. Histologic, immunohistologic and bacteriologic evaluation. Osteologie 12:333–346 15. Milosev I, Trebse R, Covac S, Cör A, Pisot V (2006) Survivorship and retrieval analysis of Sikomet metal-on-metal total hip replacements at a mean of seven years. J Bone Joint Surg Am 88:1173–1182 16. Minang JT, Areström I, Troye-Blomberg M, Lundeberg L, Ahlborg N (2006) 31-Nickel, cobalt, chromium, palladium and gold induce a mixed Th1- and Th2-type cytokine response in vitro in subjects with contact allergy to the respective metals. Clin Exp Immunol 146:417–426 17. Pandit H, Vlychou M, Whitwell D, Crook D, Luqmani R, Ostlere S, Murray DW, Athanasou NA (2008) Necrotic granulomatous pseudotumors in bilateral resurfacing hip arthroplasties: evidence for a type IV immune response. Virchows Arch 453:529–534 18. Park YS, Moon YW, Lim SJ, Yang JM, Ahn G, Choi YL (2005) Early osteolysis following second-generation metal-on-metal hip replacement. J Bone Joint Surg Am 87:1515–1521 19. Shanbhag AS, Kaufman AM, Hayata K, Rubash HE (2007) Assessing osteolysis with use of high-throughput protein chips. J Bone Joint Surg Am 89:1081–1089 20. Silva M, Heisel C, Schmalzried T (2005) Metal-on-metal total hip replacement. Clin Orthop 430:53–61 21. Toms AP, Marshall TJ, Cahir J, Darrah C, Nolan J, Donnell ST, Barker T, Tucker JK (2008) MRI of early symptomatic metal-on-metal total hip arthroplasty: a retrospective review of radiological ﬁndings in 20 hips. Clin Radiol 63:49–58 22. Willert HG, Buchhorn GH, Gobel D, Koster G, Schaffner S, Schenk R, Semlitsch M (1996) Wear behavior and histopathology of classic cemented metal on metal hip endoprosthesis. Clin Orthop 329(Suppl):S160–S186 23. Willert HG, Buchhorn GH, Fayyazi A, Lohmann C (2000) Histopathological changes around metal/metal joints indicate delayed type hypersensitivity. Preliminary results of 14 cases. Osteologie 9:2–16 24. Willert HG, Buchhorn GH, Fayyazi A, Flury R, Windler M, Koster G, Lohmann CH (2005) Metal-on metal bearings and hypersensitivity in patients with artiﬁcial hip joints. A clinical and histomorphological study. J Bone Joint Surg Am 87:28–35 25. Witzleb WC, Hanisch U, Kolar N, Krummenauer F, Guenther KP (2007) Neo-capsule tissue reactions in metal-on-metal hip arthroplasty. Acta Orthop 78:211–220

Part IV Ceramic Articulations

Fracture and Squeaking in Ceramic-on-Ceramic Bearings: Is It Really a Concern?

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Alexandra Pokorny and Karl Knahr

11.1 Historical Development of Ceramic-on-Ceramic Bearings Alumina ceramics have been in use since the 1970s. Initially, components were made of pure alumina oxide (Al2O3). After their introduction by Boutin in France [5], they were applied in Germany and Austria by Griss, Mittelmeier and Salzer [21, 36, 44, 56]. The fracture rate for the ﬁrst generation of ceramics was comparatively high with reported fracture rates of up to 13.4% [47]. This was due to a combination of material-, design- and surgical-related factors. First-generation ceramic was of low purity and density and large grain size distribution. Unfavourable designs like skirt heads or mushroom heads as well as missing bony ongrowth on cups led to increased fracture and high loosening rates. Furthermore, some retrievals showed unpredictable complex high wear rates [10]. Monobloc designs associated with loosening were soon abandoned. However, the occurrence of catastrophic failures and reports on occasional high wear rates were disquieting [4]. The reputation of ceramic as being a brittle and unsafe material in total hip arthroplasty was established (Figs. 11.1 and 11.2). Further advances in technology led to the introduction of third-generation ceramics under the trade name Biolox forte (Ceramtec, Plöchingen). According to its manufacturer, it is the most widely used ceramic material for hip arthroplasty in the world. It is produced of synthetic, ﬁne-grained high-purity alumina with minor amounts of sintering aids. Enhancements in the production process as well as quality management like hot isostatic pressing and laser etching as well as adjustments in quality management by proof testing of all components resulted in a signiﬁcant increase in mechanical strength. The fracture rate could be reduced to about 0.02% [32]. The resulting higher quality alumina featured decreased grain size, inclusions and grain boundaries and had a signiﬁcantly greater burst strength than previous ceramics. In order to create even higher mechanical-load bearing capability, Biolox delta ceramic was developed and became available in 2002. It consists of a zirconia-toughened alumina

A. Pokorny • K. Knahr (*) Orthopaedic Hospital Vienna-Speising, Speisinger Strasse 109, 1130 Vienna, Austria e-mail: [email protected]; [email protected] K. Knahr (ed.), Total Hip Arthroplasty, DOI 10.1007/978-3-642-27361-2_11, © 2012 EFORT

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Fig. 11.1 Implant failure of ﬁrst-generation ceramic heads

Fig. 11.2 Implant failure of ﬁrst-generation ceramic cups

(ZTA) and contains 75 vol.% Al2O3, 24 vol.% ZrO2 and mixed oxides (1 vol.% CrO2 and SrO). The added zirconia has the beneﬁt of increased crack resistance. It has been proven to have twice the strength of Biolox forte and lower wear rates even under adverse conditions of microseparation [32, 48] (Table 11.1, Figs. 11.3 and 11.4). The fracture rate is reported to be as low as 0.002% (Source Ceramtec TM).

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Table 11.1 Comparison of properties for different generations of ceramics BIOLOX® (since 1974) Average Variance 99.7 0.15 n.a. – Rest – 3.95 0.01 4 023 500 45

BIOLOX®forte (since 1995) Average Variance >99.8 0.14 n.a. – Rest n.a. 3.97 0.00 1.750 0.076 631 38

BIOLOX®delta (since 2004) Average Variance 81.6 0.17 17 0.1 1.4 0.01 4.37 0.01 0.560 0.036 1384 67

Variable Unit Al2O3 vol.% ZrO2 vol.% Other oxides vol.% Density g/cm3 Grain size Al2O3 mm 4-Point bending MPa strengtha E-Module GPa 410 1 407 1 358 1 Fracture MPa m1/2 3.0 0.45 3.2 0.4 6.5 0.3 toughness KICb Hardness HV1 GPa 20 – 20 – 19 – Source: Ceramtec™ a Average values measured for BIOLOX®delta from 2006 b Fracture toughness refers to the capacity of a material to resist crack propagation; KIC is the corresponding characteristic value Burst stress (kn) 100

80

60

40

20

0 1 2 BIOLOX (Since 1974)

Number of tests (7 ball heads) 3 4 BIOLOX forte (Since 1995)

5

6 7 BIOLOX delta (Since 2004)

Figs. 11.3 and 11.4 Comparison of properties and burst strength for Biolox, Biolox forte and Biolox delta (Source: Ceramtec™)

11.2 Survival of Ceramic-on-Ceramic Bearings Long-term results for ceramic-on-ceramic bearings are very promising. Petsatodis et al. conducted a retrospective analysis of a series of 100 consecutive patients (109 hips). He reported a cumulative rate of survival of 84.4% at 20.8 years. All revisions were due to

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aseptic loosening of the cup [40]. Even better results at intermediate-term follow-up have been published recently. Lusty et al. found a 99% rate of survival at 7 years postoperatively with a median wear rate of the femoral head measured at 0.2 mm3 per year. He therefore encourages the use of third-generation ceramics for primary total hip arthroplasty particularly in young and more active patients [34]. Another report found similar results at 10-year follow-up in 88 hips treated with third-generation alumina-on-alumina bearings [33].

11.3 Tribological Properties of Ceramics Ceramics show a number of tribological advantages as compared to other bearings. Most important is the signiﬁcantly lowest wear rate and friction [17, 38, 39]. Aseptic loosening due to wear is still one of the main indications for revision surgery in total hip arthroplasty [15, 41]. Volumetric wear for alumina-on-alumina bearings has been reported to be 2,000–4,000 times less than for metal-on-polyethylene combinations. Ceramic wear particles are bioinert and feature superior corrosion resistance due to the minimum risk of ionization [7]. These factors lead to the established excellent biocompatibility of ceramic components. Furthermore, Ceramic is hydrophilic and therefore features superior lubrication conditions. Alumina is one of the hardest materials and is therefore resistant to scratching. However, alumina ceramics are brittle and have no way to deform without breakage. The introduction of zirconia-toughened alumina has signiﬁcantly increased crack resistance [32, 48].

11.4 Fracture Rate for Ceramic-on-Ceramic Bearings First-generation ceramics made from pure alumina were associated with high failure rates. They showed unpredictable and inferior results with fracture rates of up to 13% [58]. Reasons were mostly a problem of inferior quality of the alumina as well as implantrelated factors like missing bony ongrowth and dislocation of the acetabular component as well as mushroom or skirt designs of the head [4]. First- and second-generation Biolox ceramics were reported to have a fracture rate of 0.026% and 0.014%, respectively [25]. Enhancements in the production process led to a signiﬁcant decrease in fractures. Willmann et al. reported a fracture rate for third-generation ceramics (Biolox femoral head) of 0.004% [58]. The rate for femoral head fractures with fourth-generation Biolox delta is even lower and is estimated at 0.002%. According to Schmalzried, it is therefore far lower than the risk of a fractured stem (0.27%) [45]. However, fractures still occur (Table 11.2). In a large study by Capello et al., a fracture rate of 0.008% for ceramic inserts and 0.017% for femoral heads in 52.000 ceramic implants used since 2003 was reported [8]. In a multicenter study by Murphy et al., 1,709 hips in 1,484 patients were evaluated,

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Table 11.2 Overview of in vivo fracture rates for Biolox forte standard inserts (Source: Ceramtec™) Fracture rate

0.030% 0.025% 0.020% 0.15% 0.10% 0.005% 0.000% Production year 2000

2001

2002

2003

2004

2005

2006

2007

2008

and a fracture rate of 0.27% for ceramic liners was identiﬁed [37]. Walter et al. reported one case of ceramic liner fracture in 2,503 alumina ceramic-on-ceramic bearings implanted between 1997 and 2004 [53]. Other studies reported not a single case of ceramic fracture at long-term follow-up. Toni et al. reported on a consecutive series of 147 patients. No osteolysis or fracture could be detected at 17-year follow-up [52]. Similar ﬁndings were published by Kim et al. for young patients and dysplastic hips [30]. Hannouche et al. conclude, that ceramic liner fracture caused by impact force during normal life is unlikely to occur in vivo [24].

11.5 Risk Factors for Ceramic Fracture A number of potential risk factors for ceramic head fracture have been identiﬁed. A mismatch between head and taper with unpredictable stress loads, damage to the metal taper at initial surgery, use of a new ball on a previously damaged taper in revision surgery, entrapped debris on the contact area between head and taper, continuing use of the original head at revision surgery and manufacturing problems like autoclave and shock cooling of the head have been identiﬁed as potential risk factors [12, 26] (Fig. 11.5). With regards to fracture of the acetabular liner, positioning of the acetabular component, impingement, contact of head and cup during repositioning as well as a position change of the liner after initial improper insertion have been related to failure [14] (Fig. 11.6).

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Fig. 11.5 Fracture of ceramic head

Fig. 11.6 Fracture of ceramic liner

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11.6 Revision Strategies Following Ceramic Fracture Although ceramic fracture is rare in contemporary ceramic implants, revision surgery can be challenging. Ceramic debris can contaminate the joint area. In a multicenter retrospective study of 105 patients, who had underwent revision surgery for ceramic head fracture, the importance of total synovectomy could be clearly documented. Only 19% of patients required repeat revision following total synovectomy as opposed to 67%, who had only received partial synovectomy. Allain et al. further propagate cup exchange in any case of ceramic fracture because microscopic ceramic particles might be embedded in it [2]. The exchange to a new ceramic head or insertion of a cobalt-chromium head have both shown satisfactory results [2]. However, the use of stainless-steel heads in revision surgery is not recommended and has led to catastrophic wear of the head related to ceramic debris [1, 2]. If the trunnion shows sign of macroscopic damage, the exchange to a cobalt-chrome head or revision head with a titanium sleeve (see Fig. 11.7) is advisable. Otherwise, peak stress loads might lead to repeat fracture if a new ceramic head is used [2, 31].

11.7 Squeaking With the problems of ceramic fractures sufﬁciently addressed by third- and fourth-generation ceramic bearings, reports on audible emissions emerged. General interest was sparked in 2006, when various publications reported a squeaking sensation emanating from ceramic-on-ceramic bearings. The incidences varied widely, ranging from 0.3% to 10.7% [28, 34] (Tables 11.3 and 11.4).

Fig. 11.7 Revision system Biolox option (Ceramtec™, Plöchingen)

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Table 11.3 Overview of incidences of squeaking 0.3% 0.7% 0.8% 2.7% 10.3% 10.7%

1/301 Secur-Fit, or Secur-Fit Plus, + Osteonics ABC cup [34] 17/2397 ABG II system, Osteonics THR, ABG II stem + Duraloc option cup, various combinations [55] 3/452 Omniﬁt stem + 4 groups: ABC insert, porous-coated shell, arc-deposited-HAcoated shell and Trident cup [8] 30/1056 Omniﬁt or Accolade stem + Trident cup [42] 18/175 Stryker ABG II stem + cup [20] 14/131 Accolade TMZF stem + Trident PSC cup [28]

Table 11.4 Overview of incidences of hip noise 20.6% 20.9% 32.8%

36/175 [20] ABG II stem and cup 9/43 [29] ABG II stem Trident cup 43/131 [28] Accolade TMZF stem + Trident PSC cup

11.7.1 Inﬂuencing Factors for Development of Squeaking Numerous factors have been reported as the cause for this phenomenon. Generally, all publications agree that the aetiology is multifactorial.

11.7.1.1 Prosthetic Design and Material Recent reports emphasize the importance of prosthetic design and material. Squeaking is caused by oscillations of the implant due to vibrations. Experimental analysis by Weiss et al. [57] has shown that these vibrations are generated by an instability of the relative motion of the components with respect to each other. Some stems were found to be more susceptible than others. But also in clinical analysis, some implant designs and materials seem to favour the spreading of vibrations. Restrepo et al. demonstrated the importance of the femoral stem component. He found an increased incidence of squeaking in patients managed with a thinner stem component with a V-40 taper neck and a stem made of titanium-molybdenumzirconium-iron alloy, thus indicating that the femoral stem plays a vital role in the development of acoustic phenomena [43]. Furthermore, the design of the cup seems to play a key role. Numerous reports on acoustic emissions from THAs with a cup design consisting of a metal rim on a ceramic liner can be found. The possible impingement between the metal rim and the neck of the prosthesis, especially in designs with a short neck, might lead to increased edge loading or wear of the bearings or even to third-body wear, which in turn can damage the surface of any bearing and cause stripe wear. Swanson et al. found a high incidence of squeaking of up to 35.6%

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for those ensleeved designs [49]. 11.1% of patients experienced an audible sensation at least once a week. Short femoral neck length seemed to favour the occurrence.

11.7.1.2 Fluid Film Disruption Chevilotte et al. conducted in vitro testing of 32-mm heads and inserts in varying conditions [9]. Interestingly, squeaking was reproducible in all dry conditions, especially with increased loading, stripe wear and metal transfer. Furthermore, in case of material transfer, squeaking could be even found in lubricated conditions, whereas in the other settings, squeaking disappeared when lubrication was introduced. Therefore, the authors concluded that a disruption of the lubrication layer is the underlying cause for the squeaking phenomenon.

11.7.1.3 Microseparation Another closely linked factor to these ﬁndings seems to be microseparation of the components. Nevelos et al. and Glaser et al. demonstrated microseparation for all bearings during normal gait [18, 38, 39]. This seems to be aggravated by a general joint laxity. Microseparation in turn leads to edge loading and increased wear of the components [10, 11]. The so-called stripe wear is formed. In an area of such wear, increased amounts of friction might be generated, thus leading to vibration.

11.7.1.4 Component Orientation Initial reports on squeaking attribute a major role to anteversion and inclination of the acetabular component. W. Walter evaluated 2,716 THAs with ceramic-on-ceramic bearings and found an increased variance in cup anteversion for squeaking hips leading to a recommendation for positioning of the acetabular component within 10° of a target of 25° operative anteversion and operative inclination of 45°. Outside this range, he determined an increased possibility of 29% for squeaking [54, 55]. In contrast, Restrepo et al. could not verify a correlation between cup anteversion or inclination and the occurrence of squeaking [43]. This ﬁnding is supported by various other reports [46].

11.7.1.5 Patient-Related Factors Walter et al. described a correlation between patient age, BMI and activity level and occurrence of squeaking, which could be found more frequently in the overweight, young and active patient [55].

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Grimm et al. reported evidence that periprosthetic bone can play a role in the generation of acoustic emissions by inﬂuencing resonance [19].

11.8 Author’s Clinical Experience Until increasing literature coverage of the squeaking sensation, we were unaware of patient reports of acoustic phenomena. Therefore, we started an analysis of our ceramic-onceramic total hip arthroplasties in 2008.

11.8.1 Materials and Method To investigate the occurrence of acoustic emissions in our patients, we conducted a retrospective study of a consecutive series of patients, who had all received the same prosthesis system (Zimmer™ Alloclassic Variall®) in combination with ceramic-on-ceramic bearings. The aim was to evaluate the nature of the noise, duration and clinical consequence. First introduction of the Alloclassic® hip system was conducted in 1979. After some modiﬁcations, the Alloclassic Variall ® system emerged and has been in use at our department since 1998. This cementless design features a rectangular titanium stem of Protasul titanium alloy TiAlNb, which creates a diaphyseal press ﬁt. Secondary stability is achieved by bone ongrowth onto the grist-blasted surface. The conical acetabular component is threaded into the bone and gains long-term stability by bone ongrowth on its rough titanium surface. This hip system was combined with 28-mm heads of alumina ceramicon-ceramic Cerasul® bearing available by Zimmer™. Cerasul® is a third-generation aluminium oxide (Al2O3) hot-isostatic-pressed ceramic, ﬁrst implanted in Europe in 1998. It is available in three head sizes: small, medium and large. The alumina Cerasul® gamma inlays were used. To date, no fracture of Cerasul® gamma inlays has been reported to Zimmer™. The fracture rate for the Cerasul® heads ranges around 1:6, 2,000 (0.01%) (Source: Zimmer™) (Fig. 11.8). Between 1998 and 2003, a consecutive series of 327 patients received 337 cementless Zimmer™ Alloclassic Variall implants at our department. This secured a minimum follow-up period of 5 years. Patients were operated by different surgeons of the same department using the standard lateral transgluteal (Bauer) approach. In order to conduct a retrospective analysis of the occurrence of audible sensations, patients received a detailed questionnaire via mail, including questions on the ﬁrst occurrence of squeaking, information on the kind of noise, duration of the phenomenon and possible negative subjective evaluation on behalf of the patient. In case of a positive reply, the patient was invited to a clinical exam and radiographic evaluation. In addition, a specialized audiography was conducted in patients, who reported audible sensations. Occurrence of noise was tested walking, bending and on clinical exam.

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Fig. 11.8 Zimmer™ Alloclassic Variall® system

11.8.2 Results Two hundred twenty-nine patients returned the questionnaire, 21 were deceased and 46 could not be contacted due to change of address or refused to participate in this study. Only one patient (0.4%), a 52-year-old female, reported a distinct squeaking, which ﬁrst occurred 98 months after implantation. Initially, it was not associated with pain, but soon aggravated. However, only the questionnaire sent by mail caused her to seek contact. She reported a squeaking occurring with every movement, which did not keep her from being physically active but was perceived as disturbing. On clinical exam, movement was painful. The subsequent X-ray showed implant failure with pelvic protrusion of the acetabular. Thirty-one (13.5%) patients reported to have experienced varying other types of noises like clicking, creaking, grinding or combinations of noises. In three cases (9.7%), a snapping of the iliotibial band could be identiﬁed. The mean onset of noise was 45.6 months postoperatively. The majority of patients (83.9%) experienced the noise with speciﬁc movements like getting up from a seated position or bending. Four patients (13.9%) reported the onset after a period of prolonged walking, and one patient (3.2%) felt a clicking noise with every movement. In some cases (16%), noise was self-limiting. Other patients could avoid the occurrence by adapting speciﬁc positions (29%). In order to validate impingement as a possible cause,

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Figs. 11.9 and 11.10 Area of stripe wear on retrieval liner and head

we evaluated the neck length of the component. However, we could not ﬁnd a signiﬁcant difference between hips-emitting noises and silent hips. Demographic analysis showed no signiﬁcant difference in gender, age or BMI between patients with noisy and silent hips. Ceramic fracture could not be detected in any case.

11.8.3 Revisions More than half of the patients (52%) who reported audible sensations felt disturbed by the noise, with one patient seeking revision surgery for this cause. She felt increasingly limited by clicking noises emanating from the hip implant. In addition, two further patients required revision surgery. One 56-year-old male patient reported a creaking sensation, which started 108 months postoperatively and was later associated with pain. Another 53-year-old female patient perceived a clicking sensation associated with pain. Ceramic components were analysed by Ceramtec™ (Figs. 11.9 and 11.10). Analysis of the retrievals showed areas of increased wear corresponding to episodes of edge loading as occurring in subluxation. In addition, a distinct area of metal transfer could be found on one of the ceramic inserts corresponding to impingement. This resulted in a total rate of revision for noise of 1.7% (four patients).

11.9 Revision Strategies for Hip Noise Toni et al. have recently published guidelines on treatment of hip noise associated with ceramicon-ceramic bearings. If a patient reports acoustic emissions and clinical examination conﬁrms the ﬁndings, then radiologic evaluation by means of X-ray or CT scan should be conducted. If ceramic fragments are radiologically documented, revision surgery is indicated. Should radiologic evaluation prove negative, Toni et al. suggest a needle aspiration of synovial ﬂuid. In case

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of ceramic fragments in the aspiration ﬂuid, revision surgery is recommended if fragments measure >5 ym. If fragments are smaller than 5 ym, close follow-up is advisable [51]. In case of positive clinical examination, but negative radiologic ﬁndings as well as negative aspiration results, normal follow-up is thought sufﬁcient. In cases where increased joint laxity might lead to subluxation and increased edge loading and therefore to increased wear, an exchange of the head to a larger neck size might be indicated. In cases where no obvious reasons for squeaking can be detected, an exchange to a metal-on-highly cross-linked polyethylene bearing has demonstrated promising results and eliminated hip noise [35]. However, there are yet no long-term results available, and adverse effects from switching from a hard-hard to a hard-soft bearing with destruction of the metal head through undetectable ceramic debris might be possible.

11.10 Safe Handlings of Ceramic Components Ceramics in THA have proven to be a reliable bearing surface. However, fractures of ceramic components still occur. This is mainly due to false handling of the components or wrong positioning of implants. Therefore, safe handling of ceramic components is crucial to a satisfactory outcome. It is important to ensure that no damage to the articular surface occurs during insertion of the liner and that the liner is placed correctly in the shell. We ensure this by using a suction device, which allows safe and exact positioning of the liner (see Figs. 11.11 and 11.12).

Figs. 11.11 and 11.12 Suction device for handling of ceramic liner

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Fig. 11.13 Avoiding damage to the taper

Fig. 11.14 Use of a shoehorn minimizes risk of damage to ceramic head

To avoid intraoperative damage to the taper, it is important to remove the protective head immediately prior to insertion of the femoral head (see Fig. 11.13) If required, trial repositioning should be conducted by using the trial head. It is necessary to ensure a clean and dry taper. Debris on the interface between taper and head has been associated with an increased risk of ceramic fractures due to areas of increased stress in loading zones. After the correct head size has been identiﬁed, the original ceramic head is inserted. Extreme care during reposition is crucial in order to avoid damage to the articulating surface. Therefore, a special device named “shoehorn” is used to ensure safe repositioning at our institution (see Fig. 11.14).

11.11 Discussion New generation of ceramics are a reliable bearing with outstanding tribological qualities. They show the lowest wear rate of all bearings and feature superior biocompatibility and are therefore recommended for the young and active patient [17, 38, 39].

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Intermediate and long-term studies report survival rates of 85–99% [33, 34, 40]. Due to improved materials and production methods, ceramic fractures are nowadays a rare phenomenon with incidences of 0.02–0.002%. When handled carefully with regards to surgical technique, it is a safe bearing and should by now have shed its unrightful reputation of being prone to fracture. Studies, which describe high incidences of squeaking or other acoustic phenomena from ceramic-on-ceramic bearings, often deal with the same speciﬁc implant groups, which seem to favour the development of acoustic emissions because of their design [28, 34, 56]. Generally, audible sensations are not limited to ceramic-on-ceramic bearings. They were ﬁrst mentioned as soon as the 1950s for the Judet acrylic hemiarthroplasty. Later on, Holzmann reported a clicking noise for metal-on-metal bearings for 18 of 117 hips [27]. A transient squeaking was described by Brockett et al. for large diameter metal-on-metal bearings as well as by Back et al. in a metal-on-metal resurfacing hip [3, 6]. Recent publications by Glaser et al. and Clarke et al. indicate that all kinds of bearings can cause acoustic sensations [10, 18]. Further reports on the emission of noises for metal-on-metal bearings and hip resurfacings support these ﬁndings [13, 16]. In general, “noisy hips” are more frequent than expected, though they hardly require intervention. But noise can be the ﬁrst sign of an underlying serious problem like implant failure, malpositioning, impingement and advanced wear and can adversely affect patient satisfaction [31]. Toni et al. reported the occurrence of noise as an early clinical sign of liner chipping or fracture or stripe wear of the head [51]. This is in line with our ﬁndings of a case of squeaking in the presence of failure of the acetabular component. We found a very low incidence of audible sensations for ceramic bearings in combination with the Alloclassic Variall® system. Therefore, we conclude that the generation of noise seems to be affected by choice of prosthetic design. High incidences linked to other implant systems are supporting this assumption and show in vivo that the generation of noises is a complex interaction between bearing and implant. The development of the new delta ceramic might be a further improvement to target the squeaking phenomenon as well as ceramic fracture. The delta ceramic consists of a combination of 82% alumina and 17% zirconia as well as 0.5% chromium oxide and 0.3% strontium. This combination improves wear characteristics and makes the bearing less prone to fracture by diffusing crack energy [32]. Delta ceramics show superior performance even under adverse conditions like microseperation in simulator studies [48]. One recent report by Hamilton et al. of a prospective, randomized, multicenter trial of 218 patients (264 hips) could not detect any case of squeaking for this type of ceramic bearing [23]. However, long-term data is still pending. Should revision of a ceramic-on-ceramic implant due to squeaking become necessary, recent data has shown that a change to metal-on-highly cross-linked polyethylene eliminates squeaking and shows promising results [35]. But long-term results are missing and possible adverse effects due to change from a hard-hard to a hard-soft bearing could soccur. In any case, if a ceramic component is used, safe primary handling of the rather delicate ceramics is crucial and is the key to a satisfactory outcome.

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22. Hamadouche M, Boutin P, Daussange J, Bolander ME, Sedel L (2002) Alumina-on-alumina total hip arthroplasty: a minimum 18.5 year follow up study. J Bone Joint Surg Am 84:69 23. Hamilton W, McAuley J, Dennis D, Blumenfeld T, Politi J (2010) THA with delta ceramic. Clin Orthop Relat Res 468:358–366 24. Hannouche D, Nich C, Bizot P, Meunier A, Nizard R, Sedel L (2003) Fractures of ceramic bearings: history and present status. Clin Orthop Relat Res 417:19–26 25. Heros RJ, Willmann G (1998) Ceramics in total hip arthroplasty: history, mechanical properties, clinical results, and current manufacturing state of the art. Semin Arthroplasty 9:114–122 26. Higuchi F, Shiba N, Inoue A, Wakebe I (1993) Fracture of an alumina head in total hip arthroplasty. J Arthroplasty 8:567–571 27. Holzmann P, Eggli S, Ganz R (2002) Metal-on-metal: all things bright and beautiful in opposition. Orthopedics 25:932 28. Jarrett CA, Ranawat AS, Bruzzone M, Blum YC, Rodriguez JA, Ranawat CS (2009) The squeaking hip: a phenomenon of ceramic-on-ceramic total hip arthroplasty. J Bone Joint Surg Am 91:1344–1349 29. Keurentjes JC et al (2008) High incidence of squeaking in THAs with alumina ceramic-onceramic bearings. Clin Orthop Relat Res 466:1438–1443 30. Kim YH, Choi Y, Kim JS (2010) Cementless total hip arthroplasty with ceramic-on-ceramic bearing in patients younger than 45 years with femoral-head osteonecrosis. Int Orthop 34(8):1123–1127, Epub 2009 Sep 26 31. Koo KH, Ha YC, Jung WH, Kim SR, Yoo JJ, Kim HJ (2008) Isolated fracture of the ceramic head after third-generation alumina-on-alumina total hip arthroplasty. J Bone Joint Surg Am 90(2):329–336 32. Kuntz M, Usbeck S, Pandorf T, Heros R (2011) Ceramic hip replacements: wear behaviour affects the outcome- a tribological and clinical approach. Tribol Total Hip Arthroplasty. doi:10.1007/987–3–642–19429–0_3 33. Lee Y-K, Ha Y-C, Yoo JJ, Koo K-H, Yoon KS, Kim HJ (2010) Alumina-on-alumina total hip arthroplasty: a concise follow-up, at a minimum of ten years, of a previous report. J Bone Joint Surg Am 92:1715–1719 34. Lusty PJ, Tai CC, Sew-Hoy RP, Walter WL, Walter WK, Zicat BA (2007) Third generation alumina-on-alumina ceramic bearings in cementless total hip arthroplasty. J Bone Joint Surg Am 89:2676–2683 35. Matar WY, Restrepo C, Javad P, Kurtz SM, Hozack WJ (2010) Revision hip arthroplasty for ceramic-on-ceramic squeaking hips does not compromise the results. J Arthroplasty 25(6 Suppl):81–86, Epub 15 Jul 2010 36. Mittelmeier H (1985) Report on the ﬁrst decennium of clinical experience with a cementless 267 ceramic total hip replacement. Acta Orthop Belg 51:367–376 37. Murphy SB et al (2006) Two-to 9 year clinical results of alumina ceramic-on-ceramic THA. Clin Orthop Relat Res 453:97–102 38. Nevelos JE, Ingham E, Doyle C, Nevelos AB, Fisher J (2000) The inﬂuence of acetabular cup angle on the wear of “BIOLOX Forte” alumina ceramic bearing couples in a hip joint simulator. J Mater Sci Mater Med 12:141–144 39. Nevelos J, Ingham E, Doyle C, Streicher R, Nevelos A, Walter W, Fisher J (2000) Microseparation of the centers of alumina-alumina artiﬁcial hip joints during simulator testing produces clinically relevant wear rates and patterns. J Arthroplasty 15:793–795 40. Petsatodis GE, Papadopoulos PP, Papavasiliou KA, Hatzokos IG, Agathangelidis FG, Christodoulou AG (2010) Primary cementless total hip arthroplasty with an alumina ceramicon-ceramic bearing: results after a minimum of twenty years of follow-up. J Bone Joint Surg Am 92(3):639–644 41. Pospischill M, Knahr K (2005) Cementless total hip arthroplasty using a threaded cup and rectangular tapered stem. J Bone Joint Surg Br 87-B(9):1210–1215 42. Restrepo C, Parvizi J, Kurtz SM, Sharkey PF, Hozack WJ, Rothman RH (2008) The noisy ceramic hip: is component malpositioning the cause? J Arthroplasty 23:643–649

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43. Restrepo C, Post Z, Kai B, Hozack W (2010) The effect of stem design on the prevalence of squeaking following ceramic-on-ceramic bearing total hip arthroplasty. J Bone Joint Surg Am 92:550–557 44. Salzer M, Zweymüller K, Locke H et al (1976) Further experimental and clinical experience 277 with aluminium oxide endoprostheses. J Biomed Mater Res 10:847–856 45. Schmalzried TP (2004) How I choose a bearing surface for my patients. J Arthroplasty 19(8 Suppl 3):50–53 46. Schroder D, Bornstein L, Bostrom MPG, Nestor B, Padgett DE, Westrich GH (2011) Ceramicon-ceramic total hip arthroplasty. Incidence of instability and noise. Clin Orthop Relat Res 469(2):437–442, Epub 18 Sep 2010 47. Sedel L (2000) Evolution of alumina-on-alumina implants: a review. Clin Orthop 379:48 48. Stewart TD et al (2003) Long term wear of ceramic-matrix composite material for hip prosthesis under severe swing phase microsimulation. J Biomed Mater Res Appl Biomater 66B:567–573 49. Swanson T, Peterson DJ, Seethala R, Bliss R, Spellmon CA Jr (2010) Inﬂuence of prosthetic design on squeaking after ceramic-on-ceramic total hip arthroplasty. J Arthroplasty 25(6 Suppl):36–42 50. Tipper JL, Firkins PJ, Besong AA, Barbour PSM, Nevelos J, Stone MH, Ingham E, Fisher J (2001) Characterisation of wear debris from UHMWPE on zirconia ceramic, metal-on-metal and alumina ceramic-on-ceramic hip prostheses generated in a physiological anatomical hip joint simulator. Wear 250:120–128 51. Toni A, Traina F, Stea S, Sudanese A, Visentin M, Bordini B, Squarzoni S (2006) Early diagnosis of ceramic liner fracture. Guidelines based on a twelve-year clinical experience. J Bone Joint Surg Am 88(Suppl 4):55–63 52. Toni A et al (2010) Osteolysis and ceramic-on-ceramic hip prostheses: “fact or fairy tale?”. In: Cobb J (ed) Modern trends in THA bearings. Material and clinical performance. Springer, Berlin/Heidelberg, pp 55–60 53. Walter WK (2005) Australian experience with ceramic systems. In: D’Antonio JA, Dietrich M (eds) Bioceramics and alternative bearings in joint arthroplasty. Steinkopff-Verlag, Darmstadt, pp 113–115 54. Walter W, Insley GM, Walter WK, Tuke MA (2004) Edge loading in third generation alumina ceramic-on-ceramic bearings. J Arthroplasty 19:402–413 55. Walter W, O’Toole GC, Walter WK, Ellis A, Zicat BA (2007) Squeaking in ceramic-onceramic hips: the importance of acetabular component orientation. J Arthroplasty 22(4):496–503 56. Walter W, Waters TS, Gillies M, Donohoo S, Kurtz SM, Ranawat AS, Hozack WJ, Tuke MA (2008) Squeaking hips. J Bone Joint Surg Am 90:102–111 57. Weiss C, Gdaniec P, Hoffmann N, Hothan A, Huber G, Morlock M (2010) Squeak in hip endoprosthesis systems: an experimental study and a numerical technique to analyse design variants. Med Eng Phys 32(6):604–660, Epub 16 Mar 2010 58. Willmann G (2000) Ceramic femoral head retrieval data. Clin Orthop 379:22–28

Long-Term Stability of Ceramic Composite in Total Hip Arthroplasty

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Bernard Masson and Meinhard Kuntz

12.1 Introduction Since the year 2000, more than 960,000 ceramic ball heads and 450,000 ceramic inserts of the new high-performance ceramic composite BIOLOX®delta have been successfully implanted. Due to the unique strength and toughness of this material, the risk of fracture has been substantially reduced when compared to conventional ceramic materials. The outstanding properties of BIOLOX®delta rely on complex reinforcing mechanisms. Therefore, it is necessary to assess if reinforcement is maintained throughout the lifetime of the artiﬁcial joint, which is anticipated to exceed more than 20 years. Like any other material which is intended for surgical applications, the suitability must be evaluated based on multiple approaches, like intrinsic mechanical material properties, biocompatibility, system compatibility and ﬁnally in vivo scoring of the surgical outcome. The basis of all progress in material development for surgical applications is the intrinsic material properties. When the surgeon decides to replace a known material by a new one, there must be sufﬁcient indication for a substantial beneﬁt. The most challenging question is to predict the reliability of the material after many years of service life. Within the scope of this chapter, the intrinsic material properties of the composite ceramic BIOLOX®delta are analysed. Lifetime can be traced back to basic principles, i.e. how can a material be damaged after many years of service. Every material degrades after many years loading in an aggressive environment. It is the challenge to create a material which preserves sufﬁcient residual reliability even under worst case conditions for many years.

B. Masson (*) Medical Products Division, CeramTec GmbH, CeramTec Platz 1-9, 73207 Plochingen, Germany e-mail: [email protected] M. Kuntz Service Center Development, CeramTec GmbH, CeramTec Platz 1-9, 73207 Plochingen, Germany e-mail: [email protected] K. Knahr (ed.), Total Hip Arthroplasty, DOI 10.1007/978-3-642-27361-2_12, © 2012 EFORT

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Due to the chemical stability, ceramics obviously provide an intrinsic advantage in comparison to other materials like metals and polymers. Ceramics are produced in the state of a fully saturated chemical bonding. There is no driving power left for further chemical interaction with the environment. Thus, typical lifetime limiting problems like corrosion or water adsorption are not relevant for high-performance and high-purity ceramics. It must be considered if there are other mechanisms which may limit the lifetime of ceramics. It is well known that like all other materials, also ceramics may suffer degradation from following distinguished events: • Fatigue – resistance against long-time static and alternating load • Ageing – resistance against hydrothermal or other chemical attack • Wear – durability under abrasive conditions In this chapter, the lifetime limiting mechanisms and the relevance for the application as a surgical implant are discussed. It is shown how lifetime of the ceramic material BIOLOX®delta can be described and evaluated. The unique microstructure and reinforcing mechanisms of the material not only support the short-term performance like fracture toughness and strength but also improve substantially the long-term reliability.

12.2 Description of BIOLOX®Delta BIOLOX®delta is an alumina-based composite ceramic. In total, 80 vol.% of the matrix consists of ﬁne-grained high-purity alumina which is very similar to the well-known material BIOLOX®forte. As it is the case in any other composite material, the basic physical properties like stiffness, hardness, thermal conductivity, etc., are mainly predetermined from the dominating phase. The new material was developed in order to increase strength and toughness and preserve all desirable properties of BIOLOX®forte which is widely used today. These properties are rigorously improved by implementation of reinforcing elements. Figure 12.1 shows the microstructure of BIOLOX®delta. Two reinforcing components are integrated in BIOLOX®delta. In total, 17 vol.% of the matrix consists of tetragonal zirconia particles. The average grain size of the zirconia is around 0.2 mm. As a further reinforcing element, approximately 3 vol.% of the matrix is built by platelet-shaped crystals of the ceramic composition strontium aluminate. The platelets stretch to a maximum length of approximately 3 mm with an aspect ratio of 5–10. The reinforcing ability of these ingredients is explained below. Additionally to the reinforcing components, there are also stabilizing elements doped to the material. Chromium is added which is soluble in the alumina matrix and which increases the hardness of the composite. The minor amount of chromium is the reason for the mauve colour of the material. Furthermore, some yttrium is added to the composite which is solved in the zirconia and which supports the stabilization of the tetragonal phase.

12 Long-Term Stability of Ceramic Composite in Total Hip Arthroplasty

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Fig. 12.1 Microstructure of BIOLOX®delta

The reinforcing elements, in particular the zirconia, substantially increase fracture toughness and strength of the material [1, 2]. Fracture toughness (KIC) is a measure for the ability of the material to withstand crack extension. Strength (sc) is deﬁned as the maximum stress within a structure that causes failure of the component. Consequently, when the fracture toughness of the alumina is increased, also the strength is directly improved. This basic principle is the concept of the development of BIOLOX®delta. The microstructure is designed in order to provide a maximum of resistance against crack extension. The beneﬁt in crack resistance which is obtained from incorporating zirconia into an alumina matrix are well known in the science of high-performance ceramics, as it is shown in Fig. 12.2. The ﬁgure represents a realistic part of the microstructure. In the case of severe overloading, crack initiation and crack extension will occur. High tensile stresses in the vicinity of the crack tip trigger the tetragonal–monoclinic phase transformation of the zirconia particles. The accompanied volume expansion leads to the formation of compressive stresses which are very efﬁcient for blocking the crack extension.

1µm

Fig. 12.2 Reinforcing mechanism in BIOLOX®delta at crack initiation and propagation

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As it is shown, this reinforcing mechanism is fully activated within a region of a few micrometres. For the macroscopic performance of the material, it is extremely important that immediately at the beginning of crack initiation, also the reinforcing mechanisms are activated. Regarding Fig. 12.2, one should keep in mind that the average distance between the reinforcing zirconia particles is approximately 0.2 mm, i.e. similar to the grain size. Thus, the reinforcement is activated immediately when any microcrack is initiated. The reinforcing ability of zirconia particles is a consequence of the phase transformation, i.e. the spontaneous change from the tetragonal to the monoclinic phase. The phase transformation is accompanied by a volume change of 4% of the zirconia particle, i.e. a linear expansion of 1.3%. Spontaneous phase transformation is a well-known principle in material science. For example, the properties of high-performance steels also rely on spontaneous phase transformation from austenite to martensite. It should be emphasized that the ability of phase transformation is the precondition for any beneﬁt of the zirconia within the material. The composite is designed such that phase transformation occurs when it is needed, i.e. in the case of microcrack initiation. In contrast to pure zirconia (which draws its high strength from the same principle), the main source of the stability of the tetragonal phase is the embedding of the zirconia particles in the alumina matrix. In contrast, the stability of pure zirconia only relies on the chemical stabilization (i.e. doping with yttria) and the grain size, which should not exceed a certain range. This is the most important distinction of the composite material BIOLOX®delta to pure zirconia. In particular, the mechanical stabilization of the stiff alumina matrix is not sensitive to any ageing effect.

12.3 Comparison of Component and Material Testing As described above, it is the objective of this chapter to show the intrinsic stability of the material BIOLOX®delta against any lifetime limiting effects. This is mainly accomplished by using well-deﬁned specimens according to the requirements of international standards for surgical materials (e.g. ISO 6474 or ASTM F 603). However, it may be useful to compare the data obtained from test specimens like bending bars to the properties of hip components. For this purpose, in Fig. 12.3, the results of ball head fracture tests and of 4-point bending tests of several powder batches are presented. The burst tests on BIOLOX®delta ball heads (Fig. 12.3 left) refer to a standard design diameter 28 mm, taper 12/14. Each individual data point in the ﬁgure represents the average value of a test series of at least seven ball heads. The strength (Fig. 12.3 right) refers to 4-point bending tests according to ASTM F 603. The strength as it is derived from bending tests represents the maximum stress in the specimen at the moment of fracture. Each individual data point represents the average of 30 specimens. As it is shown, plenty of data is available for either ball head burst tests and strength. The larger scatter in the burst tests is a consequence of the smaller number of specimens used in this test. From these data, one is able to compare the strength of the material to the performance of the components. The average burst load is 83 kN, and the average strength is 1,400 MPa.

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Burst test

4-point bending test

Average strength [MPa]

120 Burst load [kN]

100 80 60

46 kN

40 20 0 0

2

4

6 8 Batch no

10

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1,600 1,400 1,200 1,000 800 600 400 200 0 0

10 20 30 BIOLOX® delta lots

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Fig. 12.3 Burst load of BIOLOX®delta ball heads 28mm (+3,5) and strength of bending tests

Usually, the load acting on an artiﬁcial hip joint is expressed as multiples of the body weight (BW). A reasonable value for 1 BW is 1 kN (approx. 100 kg). From various experiments and calculations, it is derived that the maximum load which can occur in vivo in an extreme situation (e.g. one leg balancing of a stumble) is approximately 9 × BW. This result gives an impressive indication of the large safety margin which is provided from the use of the material BIOLOX®delta as a surgical material. On this basis, the lifetime experiments were designed. The long-term stress on the specimens was chosen such that a reasonable margin in comparison to maximum in vivo loading is provided. Thus, for the cyclic loading tests, two stress levels of 300 and 600 MPa were chosen. From the comparison discussed under Fig. 12.3, the stress level of 300 MPa is equivalent to a component loading of 18 × BW, i.e. double the maximum in vivo load (300 MPa/1,400 MPa » 18 BW/83 BW). Analogous, 600 MPa correspond to fourfold maximum in vivo load. Using these stress levels, it is analysed whether the material is able to resist extreme conditions over a lifetime relevant period.

12.4 Discussion of Lifetime Limiting Eﬀects The analysis discussed in this chapter refers to a combination of ageing and fatigue experiments. Any degradation of the material after long-term treatment is evaluated by comparison of residual strength to the as-received state.

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Ageing is a relevant issue for all zirconia-containing materials. The transformation from the tetragonal to the monoclinic phase can be triggered by the so-called hydrothermal attack [3–5]. “Hydrothermal” means that this particular ageing effect only takes place in aqueous environment at elevated temperatures. It has been shown that a critical temperature range for hydrothermal ageing is around 134–150°C. Obviously, this temperature is not realistic for human body environment. However, today, it is well accepted that the ageing in the human body environment can be simulated in an accelerated test using autoclaving conditions of two bar water steam and 134°C. Various authors claim that 1-h autoclaving conditions are equivalent to 2–4 years in the human body [1, 2]. Consequently, accelerated ageing is also required as a standard test for pure zirconia as a material for surgical implants. Usually, it is investigated whether the residual strength of the material deteriorates after ageing. The concept which is presented here does not only rely on the residual strength but also to the performance of the material at cyclic loading. Fatigue is deﬁned as the material sensitivity against cyclic loading. Limited fatigue resistance is usually observed when the materials ability of crack resistance is continuously deteriorating during the cycling. Even materials which offer plastic deformation and high crack resistance like metals can substantially lose their strength during cyclic loading and exhibit brittle fracture. In general, ceramics show higher fatigue resistance in comparison to metals. However, the fatigue effects of ceramics also depend on their speciﬁc crack resistance mechanisms. As it was shown under Fig. 12.2, the crack resistance of BIOLOX®delta is rather complex. Thus, it is necessary to demonstrate whether this material may show any degradation at cyclic loading. As a special feature of this investigation, hydrothermal ageing and fatigue are combined. According to the theoretical background, one should consider if any ageing effect may also impair the fatigue resistance or vice versa.

12.5 Result of Lifetime Experiments The experiments were designed to simulate a combination of worst case conditions on BIOLOX®delta. The specimens were prepared according to the 4-point bending conﬁguration as it is shown in Fig. 12.3 (right). As discussed above, the lifetime limiting effects ageing and cyclic fatigue were combined in these tests. Two stress levels (300 and 600 MPa) are chosen for the cyclic loading tests. The lower stress level was applied for 20 Mio cycles, the higher stress level for 5 Mio cycles. All tests were performed in Ringer’s solution. The accelerated ageing was simulated by 5- and 100-h treatment in autoclaving conditions which is equivalent to 10 and 200 years (!) in vivo. All specimens used for cyclic loading where proof tested prior to the cycling. Table 12.1 shows the test matrix including the number of specimens used. Using 30 specimens is usually required for determination of strength. However, due to the time-consuming experiments applying the cyclic loading, it was decided to use only six specimens for each cyclic loading test. After the treatment, the residual strength of the specimens was determined and compared to the initial strength. Furthermore, the monoclinic phase content was measured for each treatment.

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Table 12.1 Test matrix with number of tested samples Autoclaving (h) 0 5 100

No cyclic load 30 30 30

300 MPa 20 × 106 cycles 6 6 6

600 MPa 5 × 106 cycles 6 6 6

Table 12.2 Residual strength and monoclinic phase content after diverse treatments Autoclaving 0

5

100

No cyclic load Strength (MPa) 1,346 Monoclinic phase 18 content (%) Strength (MPa) 1,332 Monoclinic phase 22 content (%) Strength (MPa) 1,234 Monoclinic phase 30 content (%)

300 MPa 20 × 106 cycles 1,433 33

600 MPa 5 × 106 cycles 1,284 43

1,248 35

1,361 42

1,308 33

1,300 47

As the most amazing result, the yield of specimens surviving all the tests was 100% in all cases. Even most severe conditions (i.e. 100-h autoclaving, 600 MPa cyclic load) did not reveal any premature failure. It should be recalled that this stress level represents four times the highest load level at worst case conditions in vivo. We can thus conclude that the reliability of BIOLOX®delta exceeds by far the necessary requirements for reliable surgical components. Table 12.2 shows the results of the post-test analysis including residual strength and monoclinic phase content. There is a marginal natural scatter in residual strength which is always expected for ceramic materials. However, statistical analysis using Student’s t-test did not reveal any signiﬁcant deviation of all strength results. In contrast, there is a clear tendency of an increase in monoclinic phase content both after autoclaving and after cyclic loading, which is illustrated in Fig. 12.4. For example, the test series without autoclaving shows an increase of monoclinic phase content from 18% in the initial state to 43% after 5 Mio cycles at 600 MPa. It must be concluded that the cyclic mechanical loading at a high stress level (600 MPa) of almost half the strength (1,400 MPa) activated the reinforcing ability of the material. As discussed under Fig. 12.2, a high mechanical stress triggers localized phase transformation which prevents any further crack propagation. Obviously, the increased amount of monoclinic phase content does not deteriorate the strength of the material. This important conclusion is independent from the source of the phase transformation. In other words, when the phase transformation is activated either by accelerated ageing, cyclic fatigue or a combination of both, the residual strength remains on the initial level. The reported monoclinic phase content should be discussed with respect to the composition of the material. The monoclinic phase content shown in Fig. 12.4 is related to the total zirconia. As described above, the total volume content of zirconia in the alumina

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Fig. 12.4 Increase of monoclinic phase content at cyclic loading

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5 h ageing No ageing

10 0 No cycling

300 MPa 20 Mio cycles

600 MPa 5 Mio cycles

matrix is 17%. In order to assess the effect of the zirconia content, one should refer the amount of monoclinic phase relative to the total volume of the material. For example, the highest amount of monoclinic phase in a region close to the surface measured in this study is 47%. This equals a total monoclinic content of only 8% (= 47% × 17%). Obviously, even under extreme conditions, the amount of monoclinic phase in this material is well under control. In this context, it is elucidative to remind that in pure zirconia, an amount of 20% monoclinic phase is allowed according to the standard ISO 13356 already in the initial state before accelerated ageing. It is thus concluded that the speciﬁc composition of BIOLOX®delta provides inherent protection against improper phase transformation.

12.6 Conclusions The material BIOLOX®delta has been exposed to extreme conditions (accelerated ageing and cyclic loading in Ringer’s solution). It has been shown that even a combination of worst case conditions do not reveal any premature failure. Furthermore, it was shown that the residual strength remains on the initial level. A certain amount of phase transformation was observed during the tests. The highest amount of monoclinic phase relative to the total volume of the specimen was 47%. The residual strength was not affected by the phase transformation. In other studies, it was shown that BIOLOX®delta performs extremely well in severe wear tests [6]. These results are also attributed to the reinforcing mechanism in the material. These exciting results promote the conﬁdence that BIOLOX®delta offers the highest probability of long-term durability in well-designed artiﬁcial joint systems.

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References 1. Clarke IC, Pezzotti G, Green DD, Shirasu H, Donaldson T (2005) Severe simulation test for run-in ear of all-alumina compared to alumina composite THR. In: Proceedings 10th BIOLOX symposium, Washington DC, 2005, pp 11–20 2. De Aza AH, Chevalier J, Fantozzi G, Schehl M, Torrecillas R (2002) Crack growth resistance of alumina, zirconia and zirconia toughened alumina ceramics for joint prostheses. Biomaterials 23:937–945 3. Gremillard L, Chevalier J, Epicier T, Deville S, Fantozzi G (2004) Modeling the ageing kinetics of zirconia ceramics. J Eur Cer Soc 24:3483–3489 4. Hannink RHJ, Kelly PM, Muddle BC (2000) Transformation toughening in zirconia-containing ceramics. J Am Cer Soc 83(3):461–487 5. Ohmichi N, Kamioka K, Ueda K, Matsui K, Ohgai M (1999) Phase transformation of zirconia ceramics by annealing in hot water. J Cer Soc Japan 107(2):128–133 6. Pezzotti G (2006) Environmental phase stability of next generation ceramic composite for hip prostheses. Key Eng Mater 309–311:1223–1226

Ceramic-on-Ceramic Bearings in Hip Arthroplasty: A Clinical Review

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James M. Buchanan

13.1 Introduction Fixation of prosthetic implants is vital, and failure from loosening needs to be avoided if possible. Cement ﬁxation is improving with advanced insertion techniques, but long-term use of cement beyond 10 years is still a worry. To compound the worries, polythene wear will cause periprosthetic osteolysis from debris disease. Fixation using the physiological process of bony integration of synthetic hydroxyapatite (HA) will obviate the use of cement. An HA-coated implant will become integrated and thereby ﬁxed in cancellous bone. It is postulated that stem cells in the bone marrow will adhere to the HA coating and then become osteocytes, thereby ﬁxing the implant. Fixation may outlast the bearing surfaces. With over 20 years experience, results from HA ﬁxation suggest that it is a reliable system, but we know that polythene bearings continue to wear and need isolated revision. Surgeons who have used HA coating as a system of ﬁxation might be advised to review their patients regularly, regardless of the patients’ claims to be asymptomatic and particularly when they have had polythene implants in place for 15 years or more. The polythene bearings may be wearing out. Ceramic materials are hard and durable. Any ceramic debris would be expected to cause major destruction leading to osteolysis and loosening. However, this has not been observed in clinical practice. Are ceramic bearings the answer to the selection of bearing surfaces in total hip arthroplasty?

J.M. Buchanan, FRCS Emeritus Consultant Orthopaedic Surgeon, Sunderland Royal Hospital, UK Hon. Clinical Lecturer, University of Newcastle upon Tyne, UK e-mail: [email protected] K. Knahr (ed.), Total Hip Arthroplasty, DOI 10.1007/978-3-642-27361-2_13, © 2012 EFORT

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13.2 Methods In 1988, hip replacement with implants ﬁxed by hydroxyapatite (HA) bonding was commenced. The patients were assessed annually with interview, examination and plain X-ray to evaluate their progress and the efﬁcacy of HA ﬁxation. Coupled with this, the use of ceramic-on-ceramic bearings in younger patients was added to the series in 1990. A prospective study of clinical evaluation of ceramic-on-ceramic hip arthroplasty was reported at the EFORT meeting in Copenhagen in 2011. This study extended over 19 years with 626 HA-coated hip arthroplasties all with ceramic bearings. Two factors were studied. One, to establish that ﬁxation by HA osseointegration provided a stable long-lasting system of ﬁxation; the other, to observe the function of hard-on-hard ceramic bearings. Would they work in the long term without causing wear, debris disease or pseudo-tumours? In this study, the patients were invited to attend for annual review using the Harris Hip Score to assess pain and function and to have X-rays to check osseointegration. Alumina on alumina ceramic was inserted in 467 hips. The newer Zirconia Toughened Alumina (ZTA) was inserted in 169 hips. There were 118 hips still under review at 10 or more years.

13.3 Results Aseptic loosening was unusual (1 stem and 2 acetabulae (3 of 1,252 components, 0.24%)). Failure from mal-orientation with repeated dislocation occurred in six hips (0.96%). Three alumina heads (0.48%) and two alumina liners (0.32%) broke. There has been no failure of ZTA ceramic. No patients have thigh pain. Osteolysis and debris disease have not arisen. Harris hip scores show 91.2% scoring over 90 or 100. Lower scores mostly related to co-morbidity problems in other joints or medical diseases. There has been no observed third body wear or osteolysis, and no patients have developed a pseudo-tumour.

13.4 Discussion and Conclusions Fixation of implants by physiological HA bonding appears to establish that this is a secure and long-lasting solution to ﬁxation [2–4, 9–11, 19, 20]. However, ﬁxation alone is of little use if the bearing surfaces wear out. No bearing combination is perfect. Polythene debris often, but not inevitably, leads to debris disease. Metal on polythene has been shown to wear the polythene [8]. This can be observed at any time after about 10 years. Ceramic on polythene still wears the polythene being observed after 15 years. Occasionally, a polythene component may be totally destroyed.

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For the future, will the use of cross-linked polythene obviate the worries of debris disease or just postpone them? Avoiding the use of polythene would appear to be desirable especially for long-term use, and so hard-on-hard bearings must be considered. Metal-onmetal bearings function well but create their own complications [5–7]. There are now worries about ion release, especially in women of childbearing age. Additionally, might metal ion release contribute to malignant changes? Metal-on-metal bearings have already been associated with pseudo-tumours [14–17]. Ceramic-on-ceramic bearings have been in use since 1970 when they were implanted by Boutin [1]. Garino studied wear with different bearing couples and concluded that alumina–alumina caused least wear (0.005 mm/year compared with 0.2 mm/year with metal on polythene) [12]. Sedel reported on the long-term results of ceramic bearings in 2003. With negligible wear, ceramic-on-ceramic bearings in THR look attractive [18]. However, nothing is perfect. Alumina is brittle and can fracture in a very small number of cases. With the next generation of composite ceramics (Zirconia toughened alumina (ZTA)), the incidence of ceramic failure should be reduced to negligible levels (ZTA is marketed by Ceramtec as Biolox Delta®). It is 80% alumina, 18% Zirconia and 1.5% mixed oxides (CrO2, Y2O3 and SrO). Plastic debris contributes to debris disease and aseptic loosening. Hard-hard bearings should obviate this problem. Metal–metal will release ions which might be deleterious [13]. Experience with metal–metal resurfacing has highlighted problems including pseudotumours. Ceramic bearings may occasionally fracture but otherwise appear free of complications. Assessments conﬁrmed that patients remained well. Aseptic loosening of HA hips was rare at 0.24%. Failure from broken alumina components was unusual. Alumina has now been superseded by ZTA for implantation. Ceramic on ceramic is a reliable combination for bearing surfaces in patients of any age and either sex.

References 1. Boutin P (1972) Total arthroplasty of the hip by fritted alumina prosthesis. Rev Chir Orthop Reparatrice Appar Mot 58(3):229–246 2. Buchanan JM, Goodfellow S (2008) Nineteen year review of hydroxyapatite ceramic coated hip implants: a clinical and histological evaluation. Key Eng Mater 361–363:1315–1318, ISBN 1013–9826, ISBN 0–87849–457-x, ISBN-13–978–0–87849–457–6 3. Buchanan JM, Malcolm AJ (2004) Fifteen year review of hydroxyapatite ceramic coated hip implants: a clinical and histological evaluation. J Bone Joint Surg Br 86-B(Suppl 111):320 4. D’Antonio JA, Capello WN, Manley MT, Geesink R (2001) Hydroxyapatite stems for total hip arthroplasty. Clin Orthop Relat Res 393:101–111 5. Daviers AP, Willert HG, Campbell PA, Learmonth ID, Case CP (2005) An unusual lymphocytic perivascular inﬁltration in tissues around contemporary metal-on-metal joint replacements. J Bone Joint Surg Am 87A:18–27 6. Doorn PF (2000) Wear and biological aspects of metal-on-metal total hip replacements. Thesis, University Medical Centre Nijmegen, Nijmegen, October 2000

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7. Doorn PF, Mirra PF, Campbell PA, Amstutz HC (1996) Tissue reaction to metal-on-metal total hip prostheses. Clin Orthop Relat Res 329S:S187–S205 8. Dumbleton JH et al (2002) A literature review of the association between wear rate and osteolysis in total hip arthroplasty. J Arthroplasty 17:649–661 9. Furlong RJ, Osborn JF (1991) Fixation of hip prostheses by hydroxyapatite coatings. J Bone Joint Surg Br 73-B:741–745 10. Geesink RGT, Hoefnagels NHM (1992) Six years results of hydroxylapatite coated total hip replacement. J Bone Joint Surg Br 74-B:74–77 11. Geesink RGT, de Groot K, Klein CPAT (1988) Bonding of bone to apatite coated implants. J Bone Joint Surg Br 70-B:17–22 12. Greenwald AS, Garino JP (2001) Alternate bearing surfaces: the good, the bad and the ugly. J Bone Joint Surg 83-A(Suppl 2, part 2):68–72, Metal-on-metal total hip replacements 13. Jacobs JJ, Skipor AK, Doorn PF, Campbell PA, Schmalzried TP, Black J, Amstutz HC (1996) Cobalt and chromium concentrations in patients with metal-on-metal total hip replacements. Clin Orthop 329S:S256–S263 14. Kwon YM, Ostlere S, McLardy-Smith P, Gundle R, Whitwell D, Gibbons CLM, Taylor A, Pandit HS, Glyn-Jones P, Athanson N, Beard D, Gull HC, Murray DW (2009) Asymptomatic pseudotumours in patients with metal-on-metal hip resurfacing: prevalence and metal ion study. Presented at annual scientiﬁc meeting British Hip Society, Manchester, 2009 15. Laughton DJ, Jameson SS, Joyce TJ, Natu S, Logishetty R, Tulloch C, Nargol AV (2009) Adverse reactions to metal debris following large bearing metal-on-metal arthroplasty. Presented at annual scientiﬁc meeting British Hip Society, Manchester, 2009 16. Murray DW (2008) Pseudotumour after hip resurfacing. Presented at second annual U.S. comprehensive course on total hip resurfacing arthroplasty, Los Angeles, 24–25 Oct 2008 17. Pandit H, Glyn-Jones S, McLardy-Smith P, Gundle R, Whitwell D, Gibbons CLM, Ostlere S, Athanasou N, Gill HS (2008) Pseudotumours associated with metal-on-metal hip resurfacings. J Bone Joint Surg Br 90-B:847–851 18. Sedel L, Hamadouche M, Bizot P, Nizard R (2003) Long term data concerning the use of alumina on alumina bearings in total hip replacements. Key Engineering Materials 240–242:769– 772. BIOCERAMICS 15; Trans Tech Publications Ltd, Switzerland ISBN 0-87849-911-3 19. Søballe K, Hansen ES, Brockstedt-Rasmussen H et al (1990) Hydroxyapatite coating enhances ﬁxation of porous coated implants: a comparison in dogs between press-ﬁt and non-interference ﬁt. Acta Orthop Scand 61:299–306 20. Tonino A, Thèrin M, Doyle C (1999) Histology and histomorphometry around autopsy components. J Bone Joint Surg Br 81-B:148–154

Part V Miscellaneous

Study of a Titanium Dual-Mobility Socket with a Mean Follow-up of 18 Years

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Remy Philippot, B. Boyer, and F. Farizon

14.1 Introduction Prosthetic instability is currently one of the major complications occurring after implantation of a total hip arthroplasty. In order to avoid such issues, Prof. G. Bousquet designed the dual-mobility socket in 1974. The three main objectives of these dual-articulation implants were reduced wear, restoration of a physiological range of motion, and increased implant stability [4]. This concept has been shown to provide high stability after revision total hip arthroplasty and to successfully address chronic instability after total hip arthroplasty [9, 18, 19]. The initial concept was a cementless stainless steel socket with alumina coating. In 1987 and during a 5-year period, a cementless alumina-coated titanium socket was marketed. We wanted to carry out a long-term analysis of this original conﬁguration with singular tribological properties in order to precise the corresponding indications and limitations. So the purpose of our study was to analyze the results of a mean 18-year follow-up series of 103 primary cementless titanium dual-mobility sockets.

14.2 Material and Method 14.2.1 Patients We conducted a retrospective study of 103 consecutive total hip prostheses implanted in 87 patients between October 1987 and May 1993 with a mean follow-up of 18 years. The population of patients included in the series was homogenous since all patients underwent primary hip arthroplasty using the same type of implant.

R. Philippot, M.D., Ph.D. (*) • B. Boyer, M.D. • F. Farizon, M.D. Hôpital nord Saint-Etienne, Centre Hospitalier et Universitaire, Saint Etienne 42000, France e-mail: [email protected] K. Knahr (ed.), Total Hip Arthroplasty, DOI 10.1007/978-3-642-27361-2_14, © 2012 EFORT

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Fig. 14.1 Photograph of a titanium Novae

The mean age of the patients at implantation was 53 [24, 80] years. Forty-ﬁve men and 42 women were included in the series that is 63 right hips and 40 left hips. Seventy patients were classiﬁed Charnley A, 14 Charnley B, and 3 Charnley C. The etiologies included: • Primary osteoarthritis in 45 cases • Osteoarthritis secondary to hip dysplasia in 34 cases (25 grade I and II and 7 grade III and IV according to Crowe [6]), one posttraumatic osteoarthritis (acetabular fracture) and one osteoarthritis secondary to an epiphysiolysis. • Twenty-two cases of aseptic osteonecrosis of the femoral head Surgery was performed in a conventional operating room by four senior surgeons from the department. A Moore posterolateral approach was ﬁrst selected. Postoperative management was normal and consisted in early getting out of bed with complete support and discharge after 10 postoperative days. Implants used were always identical: • A dual-mobility socket of cylindrico-spherical-indented geometry, made from anodized TA6V4 titanium alloy without any ionic implantation in its concavity and a porous plasma-sprayed A1203 alumina coating on its convexity (Fig. 14.1). Shell implantation was uncemented. Press-ﬁt ﬁxation was reinforced by a 3-point ﬁxation system consisting of two Morse taper pegs impacted into the ischium and the ischiopubic ramus, respectively, and one 4.5 mm screw inserted bicortically into the ilium at 45° to the

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sagittal plane. This 3-point ﬁxation system had been designed to resist rotation and pull out forces and provide adequate primary ﬁxation. The mobile liner was made from gamma-air-sterilized ultra-high molecular weight polyethylene (UHMWPE). It was 5/8 of a sphere and articulated both with the femoral head and the metal shell. The femoral head had to be impacted into this highly retentive PE liner. All femoral heads of 22.2 mm in diameter were manufactured from cobalt-chromium. Femoral stems were all A1203 alumina-coated titanium alloy cementless screwed stems with modular plates of Proﬁl® (Serf, Décines, France) type. Anodized necks were 13 mm in diameter. All patients were seen for clinical and radiographic examination in the department. Clinical evaluation was performed at last follow-up and based on the Postel Merle d’Aubigné score [15]. Peri-prosthetic ossiﬁcation according to Brooker [5], femoral osteolysis according to Gruen, and radiolucent lines around the cup according to De Lee were radiographically assessed at last follow-up. Implant survival was evaluated at last follow-up using the actuarial method, with surgical revision for aseptic loosening as the end point. The standard error, given as a percentage, and the 95% conﬁdence intervals were calculated from the data reported in the life table. Statistical analysis was performed using nonparametric tests. Signiﬁcance was determined using the StatView statistical software (version 5.0; SAS Institute, Cary, North Carolina) and was set at p < 0.05.

14.3 Results Nineteen patients died during follow-up (22 hips), and one was lost to follow-up (1 hip). The average Postel Merle d’Aubigné score improved from 7.46 preoperatively to 16.52 at last follow-up. Results were graded as excellent by 52% of the patients, as good by 33%, and moderate to poor by 15%. Eighty patient ﬁles were radiographically analyzed at last follow-up (Fig. 14.2). The mean external diameter of the sockets was 48 mm. The average degree of cup inclination was 43° ± 8°. No migration of the acetabular cup was observed. One case of clinically symptomatic posttraumatic aseptic loosening of the acetabular cup was reported, revealing a radiolucent line exceeding 3 mm in zones I, II, and III according to De Lee and Charnley with no breakage of the mooring screw (Fig. 14.3). The absence of radiolucent lines at the bone interface was noted in 61 cups. Eighteen cups had nonprogressive radiolucent lines of less than 3 mm in zones I or II according to De Lee and Charnley. These hips were considered asymptomatic. Regarding the presence of peri-prosthetic calciﬁcations, 54 hips were Brooker grades I and II, seven were Brooker grade III, and no Brooker grade IV was reported. On the femoral side, osteolysis involving Gruen zone I was constant on all radiographs, and 64 hips showed a moderate osteolysis in Gruen zone 7. Successive images demonstrated

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Fig. 14.2 Postoperative radiograph of a THA with a titanium screw stem and a titanium Novae cup

no distal progression of osteolysis. Radiographic evidence of osteolysis was noted from the ﬁfth postoperative year. Stress shielding was observed in 38% of cases and resulted in thigh pain with no sign of femoral stem loosening or migration. On the acetabular side, failures included: • Nine cases of intra-prosthetic dislocation (Fig. 14.4) • One case of aseptic loosening of the traumatic socket Among the 9 cases of intra-prosthetic dislocation, there were 3 women and 6 men with a mean age of 50 years at revision. The etiologies were primary osteoarthritis in 9 cases. The mean acetabular cup external diameter was 50 mm. The average degree of cup inclination was 37°. The mean time to intra-prosthetic dislocation was 8.5 years (102 months ±39). There was no intra-prosthetic dislocation in patients over 70 years. For these 9 cases of intra-prosthetic dislocation, 6 cases required cup revision associated with revision of the polyethylene liner and the 3 other cases underwent isolated revision of the polyethylene mobile liner. The actuarial survival rate of the Novae® titanium socket at 18 years, when taking acetabular cup revision for aseptic loosening as the end point, was 87.4% ± 2.3% (with a conﬁdence interval superior to 95%).

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Fig. 14.3 One case of clinically symptomatic posttraumatic aseptic loosening of the acetabular cup was reported, revealing a radiolucent line exceeding 3 mm in zones I, II, and III according to De Lee and Charnley with no breakage of the mooring screw

14.4 Discussion The Novae® acetabular cup made from titanium alloy was ﬁrst introduced in September 1987 to supplement the range of Novae® (Serf, Décines, France) dual-mobility stainless steel acetabular cups. Titanium was ﬁrst used in orthopedics in the late 1980s due to its superior biocompatibility and osseointegration properties [2]. The Young’s modulus of elasticity of the titanium is close to that of the cortical bone when compared to other metals frequently used in the manufacturing of dual-mobility sockets (stainless steel, cobalt-chromium). In our study, the survival rate of the Novae® titanium socket (87.4 ± 2.3%) at 18 years is comparable to that reported in large series published in the literature; the survival rate at 15 years is 85% for the Harris-Galante I socket [11], 84.4 ± 4.5% at 15 years for the Novae® stainless steel dual-mobility socket, and 83% at 16 years for the Charnley-cemented cup [8, 12]. The long-term behavior of the Novae® titanium dual-mobility socket was thus globally acceptable since the mean age at implantation was 53 years in our series.

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Fig. 14.4 Case of intra-prosthetic dislocation

No cases of failure secondary to aseptic loosening of the acetabular component were reported with titanium sockets, unlike observed with Novae® stainless steel dual-mobility sockets, which accounts for the good survival rate despite a signiﬁcant increase in the intra-prosthetic dislocation rate. This implant provided new long-term prospects for cementless ﬁxation of dual-mobility implants due to the superior osseointegration properties of the titanium socket. In our series, the rate of aseptic loosening of the acetabular component was 1% at 18 years compared with a 9% rate at 15 years reported by aluminacoated stainless steel dual-mobility sockets with tripod ﬁxation [12]. Intra-prosthetic dislocation is a dual-mobility-speciﬁc complication. The polyethylene liner loses its retaining properties, and the prosthetic head can be expelled by decoaptation. Surgical management is required and consists in the replacement of the polyethylene liner [14]. Intra-prosthetic dislocation could be classiﬁed into two groups in our series according to its mechanisms of occurrence: intra-prosthetic dislocation induced by normal wear of the polyethylene component and intra-prosthetic dislocation secondary to blockage of the larger articulation in a context of ﬁbrosis or cam effect. Another contributing factor was classically observed in other series: the third-body effect and the increase in wear of the retentive rim in a context of acetabular loosening.

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This cause does not explain the intra-prosthetic dislocations observed with titanium sockets. The incidence rate for intra-prosthetic dislocations with the Novae® titanium socket in primary total hip arthroplasties was 9% at 18 years compared to the 4% at 15 years reported with alumina-coated stainless steel sockets. Statistically signiﬁcant intra-prosthetic dislocation risk factors (p < 0.05) were found in our series: • Young (less than 50 years old) and active patients with increased wear of the polyethylene liner • Excessive horizontal positioning of the socket (inclination of less than 40°) thus inducing a cam effect between the neck and the superior edge of the socket Some authors have reported a strong correlation between the increase in the socket size and the incidence of intra-prosthetic dislocations, which was not conﬁrmed in our series [1]. In the mid-1990s, titanium was shown to cause premature wear when articulating with polyethylene due to a very high friction coefﬁcient (poor tribological characteristics of titanium). Wear of the polyethylene liner when articulating with a titanium prosthetic head was twice higher than that reported with a stainless steel or cobalt-chromium head [10, 17]. The survival rate at 10 years was 42% for Howse II socket. Failures were attributed to wear of the polyethylene component [16]. Due to the uncertainties of that time, the Novae® titanium implant manufacturing was abandoned at the end of 1992 after a 5-year existence. As abovementioned, severe signs of wear of the Novae® titanium socket were detected associated with a high rate of femoral osteolysis at the level of the greater trochanter and calcar (macrophagical reactions to polyethylene wear debris). In large series from the literature, the rate of early dislocations during the ﬁrst 2 postoperative months ranged from 2% to 5%. But the overall long-term rate would have probably been higher to the one exposed in the short term [3]. Recurrent prosthetic instability is the main cause for surgical revision in patients over 70 years. Several series have reported the excellent stability of dual-mobility sockets implanted in primary THA and their beneﬁt in the treatment of chronic prosthetic instabilities [7, 13]. Our series conﬁrms once again the beneﬁt of dual mobility which appears as a reliable technique to prevent the occurrence of dislocation and related complications since there was no instability event at 18-year follow-up.

14.5 Conclusions Our homogenous and continuous series conﬁrms the excellent long-term behavior of dualmobility sockets in primary THA and highlights the very good stability of dual-mobility implants. However, the use of titanium implants has been shown to induce a great number of intra-prosthetic dislocations due to its disappointing tribological characteristics (high friction coefﬁcient). Therefore, the use of polished surface ﬁnish materials with a low friction

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coefﬁcient such as cobalt-chromium or stainless steel should be further promoted to reduce the incidence of polyethylene wear and its related complications, avoid intra-prosthetic dislocation, and improve quality of the femoral stem ﬁxation.

References 1. Adam P, Farizon F, Fessy MH (2005) Dual articulation retentive acetabular liners and wear: surface analysis of 40 retrieved polyethylene implants. Rev Chir Orthop Reparatrice Appar Mot 91:627–636 2. Aldinger PR, Breusch SJ, Lukoschek M, Mau H, Ewerbeck V, Thomsen M (2003) A ten to 15 year follow up of the cementless spotorno stem. J Bone Joint Surg Br 85-B:1207–1211 3. Berry DJ, von Knoch M, Schleck CD, Harmsen WS (2004) The cumulative long-term risk of dislocation after primary Charnley total hip arthroplasty. J Bone Joint Surg Am 86-A:9–14 4. Bousquet G, Gazielly D, Girardin P, Debiesse JL, Relave M, Israelia A (1985) The ceramic coated cementless total hip arthroplasty. Basic concepts and surgical technique. J Orthop Surg 1:15–28 5. Brooker AF, Bowerman JW, Robinson RA, Rileyl H (1973) Ectopic ossiﬁcation following total hip replacement: incidence and a method of classiﬁcation. J Bone Joint Surg Am 55-A:1629–1632 6. Crowe JF, Mani VJ, Ranawat CS (1979) Total hip replacement in congenital dislocation and dysplasia of the hip. J Bone Joint Surg Am 61-A:15–23 7. Farizon F, de Lavison R, Azoulai JJ, Bousquet G (1998) Results with a cementless aluminacoated cup with dual mobility. A twelve-year follow-up study. Int Orthop 22(4):219–224 8. Garellick G, Herberts P, Stromberg C, Malchau H (1994) Long-term results of Charnley arthroplasty. A 12–16-year follow-up study. J Arthroplasty 9(4):333–340 9. Guyen O, Pibarot V, Vaz G, Chevillotte C, Béjui-Hugues J (2009) Use of a dual mobility socket to manage total hip arthroplasty instability. Clin Orthop Relat Res 467(2):465–472 10. Hernandez JR, Keating EM, Faris PM, Meding JB, Ritter MA (1994) Polyethylene wear in uncemented acetabular components. J Bone Joint Surg Br 76(2):263–266 11. Kim YG, Kim SY, Park BC, Kim PT, Ihn JC, Kim ID (2005) Uncemented Harris-Galante total hip arthroplasty in patients with osteonecrosis of the femoral head. A 10–16-year follow-up study. Acta Orthop 76(1):42–48 12. Lautridou C, Lebel B, Burdin G, Vielpeau C (2008) Survival of the cementless bousquet dual mobility cup minimum 15-year follow-up of 437 total hip arthroplasties. Rev Chir Orthop Reparatrice Appar Mot 94(8):731–739 13. Leclercq S, El Blidi S, Aubriot JH (1995) Traitement de la luxation récidivante de prothèse totale de hanche par le cotyle à double mobilité de Bousquet. A propos de 13 cas. Rev Chir Orthop Reparatrice Appar Mot 81:389–394 14. Lecuire F, Benareau I, Rubini J, Basso M (2004) Intra-prosthetic dislocation of the bousquet dual mobility socket. Rev Chir Orthop Reparatrice Appar Mot 90(3):249–255 15. Merle d’Aubigne R (1990) Numerical classiﬁcation of the function of the hip. Rev Chir Orthop Reparatrice Appar Mot 76(6):371–374 16. Mohan R, Grigoris P, Johnstone F, Hamblen DL (2003) Howse II cemented titanium metalbacked acetabular cups. Poor 10 year results in 107 hips. Acta Orthop Scand 74(4):397–403 17. Nashed RS, Becker DA, Gustilo RB (1995) Are cementless acetabular components the cause of excess wear and osteolysis in total hip arthroplasty. Clin Orthop Relat Res 317:19–28 18. Philippot R, Adam P, Farizon F, Fessy MH, Bousquet G (2006) Survival of cementless dual mobility sockets: ten-year follow-up. Rev Chir Orthop Reparatrice Appar Mot 92(4):326–331 19. Philippot R, Farizon F, Camilleri JP, Boyer B, Derhi G, Bonnan J, Fessy MH, Lecuire F (2008) Survival of dual mobility socket with a mean 17 years follow-up. Rev Chir Orthop Reparatrice Appar Mot 94(1):43–48

ECiMa™ for Low Wear, Optimal Mechanical Properties and Oxidation Resistance of Hip Bearings

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Alison Traynor, David Simpson and Simon Collins

15.1 Introduction Ultra-high molecular weight polyethylene (UHMWPE) remains a widely used bearing material in total joint replacement. Peri-prosthetic osteolysis, secondary to the wear of UHMWPE, is one of the major factors that limits the long-term performance of acetabular components and highly cross-linked polyethylene (HXLPE) materials were introduced to address this issue [11]. Ionising radiation is used in the manufacture of HXLPE materials [5], and this causes the radiolytic cleavage of C-H and C-C bonds resulting in the generation of free radicals. Free radicals in the amorphous region recombine to form cross-links, the formation of which results in an initial decrease in the fatigue resistance of the material due to the reduced chain mobility of the UHMWPE that decreases the ductility of the material [22]. Free radicals in the crystalline region remain trapped and decay very slowly [12] therefore remaining active for a long period of time [13, 18]. These free radicals can migrate into the amorphous phase and cause embrittlement through reactions with diffused oxygen [17]. It is therefore necessary to stabilise free radicals in order to improve the long-term stability of HXLPE materials; however, it is important not to compromise the mechanical properties of the material. High toughness and high fatigue strength of polymers are attributed to energy-absorbing mechanisms such as cavitation and plastic deformation. A fatigue crack starts and propagates when the localised stress at the crack tip cannot be dissipated through energy-absorbing mechanisms ahead of the crack tip. The main energy-absorbing mechanism in UHMWPE is the plastic deformation of the crystalline regions, which depends on ductility and crystallinity of the material; therefore, the inﬂuence of any stabilisation methods on these properties must be considered.

A. Traynor, M.Eng. (*) • D. Simpson, Ph.D. • S. Collins, Ph.D. Technical Department, Corin Ltd, Corinium Centre, GL7 1YJ, Cirencester, Gloucestershire, UK e-mail: [email protected]; [email protected]; [email protected] www.coringroup.com K. Knahr (ed.), Total Hip Arthroplasty, DOI 10.1007/978-3-642-27361-2_15, © 2012 EFORT

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Two methods for the stabilisation of free radicals have previously been developed and are widely adopted by industry. Free radicals can be reduced by thermally annealing the HXLPE material below the melting point or they can be eliminated by re-melting the material. Thermal annealing maintains the crystallinity and mechanical properties of the material, but since it is only possible to reduce the number of free radicals, there is still the potential for oxidation to occur and this has been observed in vivo [35]. Re-melting the crystalline regions completely enables free radicals to be eliminated but also causes a reduction in the fatigue strength of the material due to a decrease in crystallinity [1, 27]. This is likely caused by the decrease in amorphous content of the polymer available for re-crystallisation after crosslinking. This limits the use of such materials to low-stress applications [24]. As a result of free radicals generated during the cross-linking process and the trade-off in properties due to the subsequent heat treatment, an alternative method is required to provide long-term oxidative stability and to maintain mechanical properties. A recent development is the use of antioxidants such as the naturally occurring antioxidant vitamin E (α-tocopherol) to stabilise radiation-induced free radicals instead of reducing them to undetectable levels by post-irradiation melting. However, an important point to note when UHMWPE is irradiated in the presence of vitamin E is that the degree of cross-linking is hindered with increasing vitamin E concentration due to the free radical scavenging ability of vitamin E [25, 31]. It is therefore necessary to optimise the vitamin E concentration and radiation dose to achieve a cross-link density comparable to 100 kGy irradiated and melted UHMWPE which has been shown to have very high wear resistance in vivo [7]. Further, another method is a mechanical annealing technique which has been developed as a method by which free radicals can be quenched whilst maintaining the crystallinity of the material. This retains the wear and fatigue resistance of the material and therefore eliminates the need for subsequent re-melting. As such, the mechanical properties of the material may be limited by the overall cross-link density and the fatigue crack propagation resistance [2, 26]. ECiMa™ is a new material developed to maintain mechanical properties minimises wear and to improve the oxidation resistance in the long term by combining the beneﬁts of vitamin E and the technology of mechanical annealing. During the manufacture of this material, vitamin E is blended into the UHMWPE resin powder, consolidated, cold-irradiated and mechanically annealed. The aim of this chapter was to compare the in vitro mechanical properties of three different UHWMPE materials; conventional UHMWPE, HXLPE and ECiMa before and after ageing. In addition, the wear rates of the three acetabular liner materials were assessed along with the oxidative stability of ECiMa under different environmental conditions.

15.2 Methods 15.2.1 Mechanical Properties The mechanical properties of ECiMa were assessed by machining dog bone specimens, 3.2 mm thick (ASTM D638 type V), from samples of the material. The production

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process involves compressing the material using a proprietary process; therefore it exhibits some degree of anisotropy. As a result, 36 specimens were machined in three different directions: parallel to the direction of consolidation, parallel to the direction of deformation and orthogonal to both of these directions. A further set of dog bone specimens (1.8 mm thick, ASTM D638 type IV) were machined from HXLPE (GUR 1020, 75 kGy, re-melt and EtO sterilised). Half of the samples were aged in accordance with ASTM F2003-02. Uniaxial tension testing was carried out as per ASTM D638 to characterise the mechanical properties of the aged and unaged material. Ultimate tensile strength (UTS), yield strength and percent elongation values were measured.

15.2.2 Fatigue Crack Propagation Six compact test specimens (ASTM E647, W = 30 mm, B = 7 mm) were machined from ECiMa and a predicate HXLPE material (GUR 1050, 100 kGy gamma radiation, re-melted at 170°C). A notch was machined into all of the test specimens using a regular notch cutter. The pre-crack was generated by slicing a razor blade into the notch. The total crack length (notch length + razor notch length) was approximately 9 mm, and the a/W ratio was 0.3. The samples were sterilised using EtO sterilisation. Half of the samples were subject to an accelerated ageing protocol in accordance with ASTM F2003-02. Testing of all of the samples was performed in accordance with ASTM F647-08 on a MTS load frame. The control mode was constant force, and DP was 99 lbs. Specimens were tested with an R-ratio of 0.1, a sinusoidal waveform and a frequency of 3 Hz. All of the testing was performed at room temperature. Fatigue crack growth was monitored with an optical microscope and the number of cycles for each growth period was recorded. Specimens were cycled until failure occurred. Fatigue crack growth rate (da/dN) and cyclic stress intensity factor (DK, the minimum stress intensity to initiate crack propagation) were calculated. Linear regression of the linear portion of the log-log data was used to determine the exponent (m) and coefﬁcient (C) æ da ö = C DK m ÷ . The Paris regime was deﬁned as the data in the crack of the Paris regime ç d N è ø growth range of 1 × 10–4 to 1 × 10–2 mm/cycle.

15.2.3 Wear Testing A total of 15 acetabular liners (Corin, UK) underwent hip simulation testing (servo-hydraulic, type C6/2-07). Three conventional UHMWPE liners (Ø32 mm, GUR 1050, gamma sterilised in nitrogen to 30 kGy) were tested to 3 million cycles (mc). Six HXLPE liners (Ø40 mm, GUR 1020, 75 kGy, re-melt and EtO sterilised) and six ECiMa liners (Ø40 mm, GUR 1020 blended with 0.1 wt% vitamin E, 120 kGy, mechanically deformed and annealed, and EtO sterilised) were tested to 5 mc. All liners articulated against CoCrMo alloy femoral heads to ASTM F75 (hot isostatically pressed and solution annealed) (Corin, UK).

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The wear testing was performed in accordance with ISO 14242 parts 1 and 2. The wear simulator used a double-peak force curve according to Paul [32], with a maximum force of 3.0 kN. The test lubricant used was calf serum with a protein content of 30 g/l supplemented with 1% (v/v) patricin as an antibacterial agent. The simulators operated at a frequency of 1 Hz and were stopped after the ﬁrst 0.5 mc and every 1.0 mc thereafter so that the volumetric wear rate could be determined gravimetrically. The location of the specimens within the simulator was periodically changed to reduce the affects of inter-station variability. Moisture uptake was monitored using loaded soak controls: one for UHMWPE and two for HXLPE and ECiMa.

15.2.4 Oxidation Following completion of the ECiMa wear testing, three of the wear tested liners were cut in half. One half of each was subject to accelerated ageing in accordance with ASTM F2003-02 (5 atm of pure oxygen at 70°C for 14 days), while the other half was tested as received. Each liner half was cross-sectioned, and a microtome was used to section 200 mm thick slices from each cross-section. Hexane extraction under reﬂux for 3 days was performed on both the aged and unaged samples prior to oxidation analysis to remove any lipid contaminants from the wear testing. To provide comparative data, samples of untested ECiMa material (n = 3) were aged in accordance with ASTM F2003-02. Post-ageing, 200 mm thick slices of material were microtomed from the centre of each specimen. Oxidation analysis was performed using a Fourier transform infrared technique in accordance with ASTM F2102-01 throughout the thickness of each liner half.

15.2.5 Cyclic Loading Under Accelerated Ageing Cyclic loading of ECiMa under accelerated ageing was performed to investigate the oxidative stability and fatigue resistance of the material during cyclic loading at an elevated temperature. HXLPE (GUR 1050, 100 kGy gamma radiation, re-melted at 170°C) was used as a control. The materials were machined into 6.5-mm thick, type-A ﬂexural fatigue specimens as per ASTM D671. For each material, there were four test specimens and three control specimens. All samples were placed in the test chamber and heated to 80°C in air for testing. The test specimens were clamped at the base while a cyclic load about the zero load line was applied at the apex of the triangular region such that the alternating stress was 10 MPa. Testing was performed at a frequency of 0.5 Hz. The heated controls were positioned close to the test specimens but not subjected to load. Tests were conducted on an MTS hydraulic mechanical testing system. The corresponding maximum and minimum loads for the displacement were recorded every 20 min. Failure of a sample was deﬁned as the visible appearance of cracks in the surface of the triangular neck region or as the complete separation of the head from the base.

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On completion of 1.5 mc or when a test sample failed, the test sample was removed from the chamber for oxidation analysis along with a heated control sample. Samples were analysed using FTIR as per ASTM F2102 to determine the oxidation proﬁle throughout the thickness of the material. Thin sections were cut using a microtome from the constant stress triangular region for analysis. Infrared spectra were collected in 100-mm intervals with each spectrum recorded as an average of 32 individual infrared scans. Three thin sections from each sample were analysed. Oxidation proﬁles were quantiﬁed as a function of depth from a free surface after the samples were boiled in hexane for 16 h and dried in a vacuum to remove any absorbed species that could interfere with the oxidation measurement.

15.3 Results 15.3.1 Mechanical Properties The average of the UTS, yield strength and percent elongation for the three directions for aged and unaged ECiMa and HXLPE are presented in Table 15.1 alongside previously published data for a conventional UHMWPE. There was an increase in UTS, yield strength and percent elongation of 12%, 10% and 8% respectively, for unaged ECiMa compared to HXLPE. Following ageing of the ECiMa and HXLPE samples, there was minimal change in all three mechanical properties, and the corresponding increases for ECiMa compared to HXLPE were 13% for UTS, 12% for yield and 7% for elongation.

15.3.2 Fatigue Crack Propagation The data plots for the fatigue crack propagation analysis are shown in Figs. 15.1 and 15.2 for the predicate HXLPE and ECiMa samples before and after ageing. Analysis of the data for the stress intensity factor at crack inception and the Paris regime parameters were computed as detailed in Table 15.2.

Table 15.1 Comparison of mechanical properties UHMWPE GUR 1020 [9] HXLPE Unaged UTS (MPa) 57 ± 3.7 49.44 ± 3.24 Yield (MPa) 22.1 ± 0.5 20.32 ± 0.26 Elongation (%) 418 ± 19 320.02 ± 9.32

Aged 46.91 ± 1.36 20.36 ± 0.15 311.82 ± 4.78

ECiMa Unaged 55.18 ± 5.88 22.41 ± 1.77 345.88 ± 59.39

Note: ECiMa data presented is the average of the directions tested

Aged 53.12 ± 6.78 22.88 ± 1.76 334.12 ± 59.70

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1.00E-01

15

HXLPE_1 HXLPE_2 HXLPE_3 HXLPE_AGED_1 HXLPE_AGED_2 HXLPE_AGED_3

da/dN [mm/cycle]

1.00E-02

1.00E-03

1.00E-04

1.00E-05

1.00E-06 1

10

ΔK [MPa m1/2]

Fig. 15.1 Fatigue crack propagation data for the predicate HXLPE before (closed symbols) and after (open symbols) accelerated ageing 1.00E-01 ECiMa_1 ECiMa_2 ECiMa_3 ECiMa_AGED_1 ECiMa_AGED_2 ECiMa_AGED_3

da/dN [mm/cycle]

1.00E-02

1.00E-03

1.00E-04

1.00E-05

1.00E-06

1

10

ΔK [MPa m1/2]

Fig. 15.2 Fatigue crack propagation data for the ECiMa before (closed symbols) and after (open symbols) accelerated ageing

15.3.3 Wear Testing Figure 15.3 shows the wear rates for the three different materials tested. There was a 95% and an 83% reduction in the wear rate for the ECiMa liners compared to the conventional UHMWPE and HXLPE liners, respectively.

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Table 15.2 Stress intensity factors and Paris regime parameters for both materials

Unaged

Aged

Group

Exponent, m

Coefﬁcient, C

DKincep(MPa m1/2)

HXLPE – 1 HXLPE – 2 HXLPE – 3 ECiMa – 1 ECiMa – 2 ECiMa – 3 HXLPE – 1 HXLPE – 2 HXLPE – 3 ECiMa – 1 ECiMa – 2 ECiMa – 3

8.91 9.35 10.97 8.93 7.64 8.12 8.95 8.03 7.37 7.59 7.96 7.35

2.87E-05 7.82E-05 1.52E-04 7.16E-06 1.14E-05 6.22E-06 2.91E-04 1.42E-04 1.42E-04 1.60E-05 1.64E-05 2.09E-05

1.07 1.09 1.17 1.19 1.21 1.17 1.06 1.09 1.01 1.16 1.19 1.19

50 45 Wear rate mm3/mc

40 35 30 25 20 15 10 5 0 UHMWPE

HXLPE Material

ECiMa

Fig. 15.3 Comparison of wear rate (mm3/mc) for 3 different polyethylene materials

15.3.4 Oxidation All of the oxidation values for the wear tested ECiMA liners, before and after ageing (Fig. 15.4), and the aged, untested ECiMa samples (Fig. 15.5) were negative, which shows oxidation levels below the level of detection throughout the thickness of the samples.

15.3.5 Cyclic Loading Under Accelerated Ageing Both of the materials pre-testing showed no signiﬁcant levels of oxidation. The HXLPEheated controls showed levels of oxidation approximately twice that of the pre-test control,

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0.00

15

0

1000

2000

3000

4000

5000

6000

−0.01

Oxidation Index [ ]

−0.02 −0.03 −0.04 −0.05 −0.06 −0.07 −0.08 −0.09

ECiMa_wear_1 ECiMa_wear_aged_1

−0.10

ECiMa_wear_2 ECiMa_wear_aged_2

ECiMa_wear_3 ECiMa_wear_aged_3

Depth location (μm)

Fig. 15.4 Oxidation index proﬁles for unaged and aged ECiMA Wear Test Samples 0.5 HXLPE_1 HXLPE_2 HXLPE_3 ECiMa_1 ECiMa_2 ECiMa_3

0.4

Absorbance [ ]

0.3

0.2

0.1

0 0

1,000

2,000 3,000

4,000

5,000

6,000

7,000

8,000

9,000 10,000

-0.1 -0.2

Depth locator [µm]

Fig. 15.5 Oxidation index proﬁles for aged ECiMA and HXLPE from the surface to the bulk

while the HXLPE-tested specimens showed oxidation levels four to ﬁve times greater than the heated control. All four ECiMa samples completed 1.5 mc cyclic loading, and there was no detectable oxidation for the test or heated control specimens. Two of the HXLPE samples completed 1.5 mc, while the other two failed by fracture at 1.313 and 1.233 mc. Average oxidation indices for all of the samples are shown in Fig. 15.6.

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0.35 Pre-test control Heated controls Test specimen

Average oxidation (A.U.)

0.30 0.25 0.20 0.15 0.10 0.05

_4 XL H

PE XL H

PE

_3

** _2 PE XL H

XL H

EC

iM

PE

a_

_1

*

4

3 a_ iM EC

a_ iM EC

EC

iM

a_

1

2

0.00

Fig. 15.6 Average oxidation for all samples. * and ** indicate samples which failed during testing

15.4 Discussion Conventional UHMWPE has good mechanical properties such as high fatigue strength which makes it suitable for use as a total joint replacement bearing material. However, peri-prosthetic osteolysis secondary to the wear limits the long-term performance of the material. HXLPE materials were introduced to overcome such limitations but there are concerns related to the use of these materials for challenging designs such as acetabular cups and posterior stabilized knees. Use of these materials in such applications can lead to rim fracture [8, 21, 34] due to a decrease in mechanical properties (presumably as a result of decreases in chain mobility with increased cross-linking) and oxidation in the long term as a result of residual free radicals [6, 17]. Antioxidants such as vitamin E have been shown to be able to protect HXLPE materials from oxidation caused by residual free radicals as a result of ionising radiation [28]. Due to this improved oxidation resistance coupled with improved fatigue strength [24] there is increased research focus on the use of vitamin E and other antioxidants in medical grade UHMWPE [15, 20, 33]. This study has assessed the in vitro performance of a new vitaminE-based HXLPE, ECiMa which has been introduced to overcome the existing concerns associated with UHMWPE and HXLPE materials. This material has been developed to obtain sufﬁcient cross-link density to achieve wear resistance, improved strength and longterm oxidative stability. Previous studies have shown radiation cross-linking to reduce the wear of UHMWPE in vitro [19, 23] and as a result, the occurrence of osteolysis due to UHMWPE wear may

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be reduced [3]. This reduction in wear is corroborated by the results presented during this study which indicate a reduction in wear rate for HXLPE and ECiMa in comparison to UHMWPE. It is also known that when vitamin E is blended with polyethylene prior to irradiation the cross-linking efﬁciency is hindered. It has also been shown that vitamin E concentrations equal to or above 0.3 wt% prevent the necessary cross-link density needed for improved wear resistance [29]. The results presented here demonstrate that 0.1 wt% vitamin E in combination with 120 kGy irradiation is sufﬁcient to enable a signiﬁcant reduction in the wear rate of ECiMa in comparison to UHMWPE and HXLPE. There are concerns regarding the decline in mechanical properties of HXLPE materials when compared to gamma-sterilised UHMWPE [10]. In particular, there is a reduction in fatigue resistance as a result of post-irradiation melting (necessary to remove the residual free radicals that would otherwise cause oxidative embrittlement in the long term). These concerns are especially heightened in component geometries with stress risers such as acetabular cups and posterior stabilized knees [30]. This work aimed to address these concerns by testing the mechanical properties of ECiMa. Encouragingly, these test indicated that the mechanical properties of ECiMa were not substantially degraded and were more comparable to conventional UHMWPE than HXLPE. Further to this, following an aggressive ageing protocol the ECiMa material maintained the mechanical properties of the unaged condition. This is in part due to the high crystallinity achieved from mechanical annealing during the manufacture of ECiMa. When the fatigue strength of the material was examined ECiMa demonstrated a signiﬁcantly higher crack inception threshold than HXLPE after accelerated ageing. This is likely to be due to the post-irradiation melting which decreases the chain mobility and hence the amorphous content available for recrystallisation post-cross-linking. In order to preserve the material properties over the lifetime of the device it is necessary to retain the oxidation resistance of the material. The oxidation analysis presented for ECiMa has indicated a high level of through-thickness oxidation resistance for the ECiMa specimens even after being subject to an aggressive ageing protocol and cyclic loading. This implies that the presence of a vitamin E will act as an ‘active stabilization’ reservoir that can protect the material from oxidation in the long term. This is in-line with the increasing body of evidence that the presence of an antioxidant in medical grade UHMWPE is beneﬁcial for preserving the material properties in the long term [4, 15, 16]. This data supports previous studies of a similar HXLPE material which contained 0.1 wt% vitamin E and demonstrated good oxidation resistance throughout the thickness of the material [9]. Conversely, even though the HXLPE material should contain no detectable free radicals, both elevated temperature and cyclic loading during the environmental stress cracking testing caused the material to oxidise resulting in the failure of two test specimens. The improved oxidation resistance of ECiMa in comparison to HXLPE is likely to be due to the free radical scavenging ability of vitamin E. This evidence is in support of the use of antioxidants to eliminate the need for post-irradiation melting. Some concerns have been raised regarding the incorporation of vitamin E into UHMWPE however, vitamin E is a naturally occurring antioxidant. Taking into consideration a component manufactured from ECiMa with a total mass of 50 g, this equates to 50 mg of vitamin E. Vitamin E toxicity is associated with doses >400 IU/day over a long period of time. Even if all of the vitamin E was to elute from the component in 1 day this is still signiﬁcantly less than 400 IU/day [14].

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The results of this study have demonstrated that the addition of vitamin E to polyethylene can provide a material with superior mechanical properties without sacriﬁcing wear resistance and provide increased oxidation resistance compared to UHMWPE without antioxidants. Further to this, these properties are maintained in the long term.

15.5 Conclusion UHMWPE has good mechanical properties which make it suitable as a bearing material for total joint replacement; however, it is limited by wear and osteolysis. HXLPE materials introduced to overcome the limitations associated with UHMWPE have demonstrated low wear but are limited by lower mechanical properties and concerns over oxidation resistance in the long term. Vitamin E incorporated into UHMWPE provides a potential solution, and in vitro testing has been performed to evaluate mechanical performance and oxidation resistance of such a material. The reduced wear rate during in vitro hip simulation of ECiMa compared to conventional UHMWPE means that it is possible that this material may reduce wear related osteolysis in vivo. Coupled with improved mechanical properties and long-term oxidation resistance in comparison to HXLPE, this makes ECiMa a promising next-generation UHMWPE bearing material. It is now necessary to support this body of in vitro test data with clinical data.

References 1. Baker DA, Hastings RS, Pruitt L (2000) Compression and tension fatigue resistance of medical grade ultra high molecular weight polyethylene: the effect of morphology, sterilisation, aging and temperature. Polymer 41(2):795–808 2. Baker DA, Bellare A, Pruitt L (2003) The effects of degree of crosslinking on the fatigue crack initiation and propagation resistance of orthopaedic grade polyethylene. J Biomed Mater Res A 66A:146–154 3. Calvert GT, Devance PA, Fielden J, Adams K, Horne JG et al (2009) A double-blind, prospective, randomized controlled trial comparing highly cross-linked and conventional polyethylene in primary total hip arthroplasty. J Arthroplasty 24(4):505–510 4. Costa L, Bracco P, Carpentieri I et al (2009) On post-irradiation oxidation of vitamin E-stabilized UHMWPE. In: Transactions of the 55th annual meeting of the Orthopaedic Research Society, Las Vegas, 2009 5. Crowninshield RD, Muratoglu O (2008) How have new sterilisation techniques and new forms of polyethylene inﬂuenced wear in total joint replacement?. J Am Acad Orthop Surg 16(Suppl 1):S80–S85 6. Currier BH, Currier JK, Mayor MB et al (2007) Evaluation of oxidation and fatigue damage of retrieved cross-ﬁre polyethylene acetabular cups. J Bone Joint Surg Br 89(9):2023–2029 7. Digas G, Karrholm J, Thanner J et al (2004) Highly cross-linked polyethylene in total hip arthroplasty: randomised evaluation of penetration rate in cemented and uncemented sockets using radiostereometric analysis. Clin Orthop Relat Res 429:6–16 8. Duffy P, Wannomae KK, Rowell SL et al (2009) Fracture of a cross-linked polyethylene liner due to impingement. J Arthroplasty 24(1):158e15–158e19 9. Dumbleton JH, D’Antonio JA, Manley MT et al (2006) The basis for a second-generation highly cross-linked UHMWPE. Clin Orthop Relat Res 453:265–271

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10. Halley D, Glassman A, Crowninshield R (2004) Recurrent dislocation after revision total hip replacement with a large prosthetic femoral head - a case report. J Bone Joint Surg Am 86:827–830 11. Jacobs CA, Christensen CP, Greenwald AS et al (2007) Clinical performance of highly crosslinked polyethylenes in total hip arthroplasty. J Bone Joint Surg Am 89(12):2779–2786 12. Jahan MS, King MC, Haggard WO et al (2001) A study of long-lived free radicals in gammairradiated medical grade polyethylene. Radiat Phys Chem 62:141–144 13. Keyser R, Tsuji K, Williams F (1968) Trapped electrons in gamma-irradiated polyethylene identiﬁed by electron spin resonance spectroscopy. Macromolecules 1:289–290 14. Jarrett BT, Cofske J, Rosenberg AE et al (2010) In vivo biological response to vitamin E and vitamin E doped polyethylene. J Bone Joint Surg Br 92(16):2672–2681 15. King R, Narayan VS, Ernsberger C (2010) Characterisation of gamma-irradiated UHMWPE stabilised with a hindered phenol antioxidant. In: Transactions of the 55th annual meeting of the Orthopaedic Research Society, Las Vegas, 2010 16. Kurtz SM (2009) UHMWPE biomaterials handbook: ultra high molecular weight polyethylene in total joint replacement and medical devices. Elsevier/Academic Press, Burlington 17. Kurtz SM, Hozack W, Purtill JJ et al (2006) Signiﬁcance of in vivo degradation for polyethylene in total hip arthroplasty. Clin Orthop Relat Res 453:47–57 18. Lawton E, Balwit J, Powell R (1960) Paramagnetic-resonance studies of irradiated highdensity polyethylene. II. Effect of irradiation dose on the radical species trapped at room temperature. J Chem Phys 33(2):405–412 19. McKellop H, Shen FW, Lu B et al (1999) Development of an extremely wear-resistance ultra high molecular weight polyethylene for total hip replacements. J Orthop Res 17(2):157–167 20. Micheli BR, Wannomae K, Ghali B et al (2010) Viability of an Irganox 1010 UHMWPE blend for use in total joint arthroplasty. In: Transactions of the 55th annual meeting of the Orthopaedic Research Society, Las Vegas, 2010 21. Moore KD, Beck PR, Petersen DW et al (2008) Early failure of a cross-linked polyethylene acetabular liner – a case report. J Bone Joint Surg Am 90(11):2449–2504 22. Muratoglu O, Bragdon CR, O’Connor D et al (1999) Uniﬁed wear model for highly crosslinked ultra-high molecular weight polyethylenes (UHMWPE). Biomaterials 20(16):1463–1470 23. Muratoglu O, Bragdon CR, O’Connor D et al (2001) A novel method of cross-linking ultrahigh molecular-weight polyethylene to improve wear, reduce oxidation, and retain mechanical properties. J Arthroplasty 16(2):149–160 24. Oral E, Wannomae KK, Hawkins N et al (2004) Alpha-tocopherol-doped irradiated UHMWPE for high fatigue resistance and low wear. Biomaterials 25(24):5515–5522 25. Oral E, Greenbaum ES, Malhi AS et al (2005) Characterisation of irradiated blends of a-tocopherol and UHMWPE. Biomaterials 26(33):6657–6663 26. Oral E, Christensen SD, Malhi AS et al (2006) Wear resistance and mechanical properties of highly cross-linked, ultrahigh-molecular weight polyethylene doped with vitamin E. J Arthroplasty 21(4):580–591 27. Oral E, Rowell SL, Muratoglu O (2006) The effect of a-tocopherol on the oxidation and free radical decay in irradiated UHMWPE. Biomaterials 27(32):5580–5587 28. Oral E, Wannomae KK, Rowell SL et al (2008) Diffusion of vitamin E in ultra-high molecular weight polyethylene. Biomaterials 28(35):5225–5237 29. Oral E, Godleski Beckos C, Malhi AS et al (2008) The effects of high dose irradiation on the cross-linking of vitamin E-blended ultrahigh molecular weight polyethylene. Biomaterials 29(26):3557–3560 30. Oral E, Bassem WG, Rowell S et al (2010) A surface crosslinked UHMWPE stabilized by vitamin E with low wear and high fatigue strength. Biomaterials 31:7051–7060 31. Parth M, Aust N, Lederer K (2008) Studies on the effect of electron beam radiation on the molecular structure of ultra-high molecular weight polyethylene under the inﬂuence of a-tocopherol with respect to its application in medical implants. J Mater Sci Mater Med 13(10):917–921

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32. Paul JP (1966) Forces transmitted by joints in the human body. Proc Inst Mech Eng 181(37):8–15 33. Senyurt AF, Warner D, Narayan VS (2010) Mechanical properties of antioxidant stabilised UHMWPE at 80 and 115 kGy. In: Transactions of the 55th annual meeting of the Orthopaedic Research Society, Las Vegas, 2010 34. Tower SS, Currier JH, Currier BH et al (2007) Rim cracking of the cross-linked Longevity polyethylene acetabular liner after total hip arthroplasty. J Bone Joint Surg Am 89: 2212–2217 35. Wannomae KK, Bhattacharyya S, Freiberg A et al (2006) In vivo oxidation of retrieved crosslinked ultra–high-molecular-weight polyethylene acetabular components with residual free radicals. J Arthroplasty 21(7):1005–1011

Index

A Adverse reaction to metal debris (ARMD), 10 ALVAL. See Aseptic lymphocyte dominated vasculitis associated lesions (ALVAL) Articular surface replacement (ASR) arc angles, 81 cup inclination, 81 lower blood metal, 81 XL systems, 74 Articulation related failure catastrophic wear, 10 destroyed ceramic head, 10 low wear bearing surfaces, 9 malposition, 15 materials, 9 osteolysis and head eccentricity, 10 revision ceramic on ceramic, 13–14 decision-making factors, 11–12 metal on metal, 13 PE, 12 treatment, 11 X-PE liners, 10 x-rays, 14, 15 Aseptic lymphocyte dominated vasculitis associated lesions (ALVAL), 10–11 ASR. See Articular surface replacement (ASR) B BIOLOX® delta, 127, 129 chromium, 146 crack extension, 147 description, 146 fracture toughness and strength, 147 microstructure, 146, 147 physical properties, 146 reinforcing mechanism, 147, 148 zirconia particles, 148 Biolox Delta alumina matrix composite bearings, 5 Biolox Forte alumina ceramic-on-ceramic bearings, 5 Birmingham hip resurfacing (BHR), 81

C Ceramic composite, long-term stability BIOLOX® delta, 146–148 component and material testing ball head fracture, 148, 149 burst tests, 148 stress levels, 149 degradation, 146 description, 145 lifetime experiments autoclaving, 151, 152 bending tests, 149, 150 inherent protection, 152 monoclinic phase, cyclic loading, 151, 152 phase transformation, 151 residual strength and monoclinic phase, 151 test matrix, 150, 151 lifetime limiting effects fatigue, 150 human body environment, 150 hydrothermal, 150 long-term treatment, 149 Ceramic-on-ceramic bearings Biolox delta, 127–128 clinical review alumina, 157 aseptic loosening, 156 debris, 155 fixation, 155 HA bonding, 156 Harris hip scores, 156 methods, 156 plastic debris, 157 prosthetic implants, 155 delta ceramics, 141 demographic analysis, 138 description, 127 fracture rate alumina, 130 femoral heads, 130 in vivo, 130, 131 osteolysis, 131

K. Knahr (ed.), Total Hip Arthroplasty, DOI 10.1007/978-3-642-27361-2, © 2012 EFORT

183

184 Ceramic-on-ceramic bearings (cont.) handlings intraoperative damage, 140 shoehorn, 140 suction device, 139 hip noise, 138–139 implant failure, 127, 128 laser etching, 127 materials and method prosthesis system, 136 retrospective analysis, 136 Zimmer™ Alloclassic Variall® system, 136, 137 noises, 137 pelvic protrusion, 137 properties and burst strength, 128, 129 reputation, 127, 128 revision breakage, 13–14 stable cup, 13 strategy, 133 risk factors, 131–132 squeaking, 133–136 stripe wear, retrieval liner and head, 138 survivorship, 129–130 transient squeaking, 141 tribological properties, 130 wear rate, 5 Ceramic-on-metal bearings, 4–5 Conventional vs. sequentially cross-linked polyethylene liners bone resorption, 33 larger femoral head sizes, 33–34, 36 materials and methods liners and femoral heads, 34, 35 six-station hip wear simulator, 34 wear testing, 34 results average gravimetric wear, 35, 36 X3T liners wear, 35 simulator studies, 37 Cross-linked polyethylene (X-PE) breakage, 10 failures, 36–37 larger femoral heads, 34, 36 THR, 33 wear and osteolysis reduction acetabular osteolysis, 65, 66, 68 annual wear rates, 65 duration vs. conventional PE, 67–68 HXLPE, 68 patient characteristics and implant parameters, 64 patients and methods, 61–63

Index randomization, 64 RCTs, 66 total linear head penetration vs. duration and conventional PE, 64–65 wear rates, 37, 67 D Delayed-type hypersensitivity (DTH) CoCr debris, 113 Sikomet articulation and ceramic-onpoly-ethylene, 122 T-cells, 122 Durom. See Large-diameter metal-on-metal cup (LDMOM) and standard stem E ECiMa™ annealing technique, 170 antioxidants, 177 average oxidation, samples, 175–177 fatigue crack propagation, 173–175 free radicals, 170 HXLPE, 178 ionising radiation, 169 mechanical properties, 173 methods average oxidation, samples, 172–173 fatigue crack propagation, 171 mechanical properties, 170–171 oxidation, 172 wear testing, 171–172 oxidation, 175, 176 peri-prosthetic osteolysis, 169 UHMWPE, 177 vitamin E, 178, 179 wear testing, 174, 175 Elongation at break (EAB), 24, 25 F Free radicals crystalline region, 169 HXLPE materials, 169, 170 radiation stabilisation , 170 H Harris hip scores (HHS), 62, 64, 156 Highly cross-linked polyethylene (HXLPE) fatigue crack, 173, 174 ionising radiation, 169 mechanical properties, 173 stress intensity, 175 vitamin-doped, 27

Index Hip prostheses ceramic-on-ceramic bearings, 5 ceramic-on-metal bearings, 4–5 metal-on-metal bearings, 4 polyethylene bearings head size, 3 osteolysis, 5 wear rate, 4 HXLPE. See Highly cross-linked polyethylene (HXLPE) HXLPE isoelastic monoblock pressfit cup, oxidation prevention ceramic-on-ceramic bearings, 22 clinical documentation, 25 hip simulator testing inlays, 24 materials, 24 test fluid, 24 mechanical properties accelerated ageing, 25, 26 tensile testing, 25, 26 mechanical testing, 23–24 RM Pressfit vitamys cup, 23 UHMWPE and HXLPE, 22, 23 vitamin-doped HXLPE material, 22 vitamys material, 22 wear rates accelerated ageing, 27 clinical follow-up, 27–29 cross-linking, 26–27 head material and diameter, 27 I Immunological adverse reaction antibodies, immunohistochemical evaluation, 115, 116 Bicon cups, 120 CD3 and CD68, 121–122 ceramic-on-polyethylene bearing, 116 CoCr debris, 113 DTH, 122 fibrin exudation, neo-capsule, 121 IV-delayed hypersensitivity, 120 metal hypersensitivity, 116 Milosev’s series, 121 MoM and CP revision, 115, 117–118 MoM THAs, 113 necrosis, synovial membrane, 115, 119 patients cementless Bicon-Plus, 114 ceramic femoral head, CP, 114 ChemMate™ Dako EnVision™, 115 CP and MoM, 114 giant cells and neutrophils, 115

185 lymphocytic infiltration, 115 periprosthetic tissues, 114 primary implantation, THA, 114 periprosthetic osteolysis, 113 perivascular infiltration, lymphocytes, 120 perivascular lymphocytic infiltration, 115, 119 Sikomet articulation, 121 Sikomet bearing, 119 T and B-lymphocytes, 115, 120 T-suppressor, 115, 121 K Kaplan-Meier (KM) method, 102 L Large-diameter metal-on-metal cup (LDMOM) and standard stem cemented stem, 92 clinical assessment, 92 data collection, 93 Durom acetabular component, 91 LHMOM, 91 longevity and pseudotumors, 94 low threshold patients acetabular cup, 96 cup loosening, 95 loose stems, 95 metallosis, 95 materials and methods, 91–92 opening angle, 91–92 osteoarthritis (OA), 94 prosthesis infection, 94 radiographic analysis, 94 radiological analysis anteroposterior pelvic and lateral radiographs, 92 cup inclination, 92 heterotopic ossification, 93 loosening definition, 92 radiographs, 92–93 revision rate, 95 Trendelenburg sign, 93 M Metal-backed cup, 99–100 Metal-on-metal bearings acetabular cup, 73 femoral bone stock, 73 imaging, soft tissues, 85 immunological adverse reaction ( see Immunological adverse reaction) measuring component position, 84–85

186 Metal-on-metal bearings (cont.) MHRA and ASR, 74 pathogenesis, 73–74 revision, 13 soft tissue reactions pseudotumour, 86–87 revision surgery, 87–88 wear and ion levels chromium and cobalt, 74, 75 component design, 81–82 diametric size tolerance, 76 high bearing surface, 77–78 linear/volumetric measurement, 76 material loss, large diameter, 83–84 parts per billion (ppb) and micrograms per litre (mg/L), 74 patient factors, 83 roundness measurement and CMM, 76 sensitivity and specificity, 76 soft tissue pathology, 74, 75 surgical positioning (see Surgical positioning) wear rate, 4 Milosev’s series, 121 Mooring screw, 163, 165 N Novae® acetabular cup, 165 O Orthopaedic arthroplasty. See Vitamin Eblended UHMWPE P Perkin-Elmer DSC6 differential scanning calorimeter, 43 Perkin-Elmer SPECTRUM SPOTLIGHT 300 auto-image microscope, 44 Polyethylene (PE) bearings head size, 3 revision, 12 wear rate, 4 Polyethylene (PE) wear anteroposterior (AP) radiograph, 101, 102 aseptic loosening, 106 cemented hip prostheses, 99 conventional UHMWPE, 107–108 femoral head, 101 head penetration rate, 101 heterogeneity, 106 highly cross-linked polyethylene (HXLPE), 105 hydroxyapatite (HA), 99 implant failure

Index KM survival estimation, 104, 105 liner and related revision, 103, 104 index surgery and UHMWPE liners, 105 Kaplan-Meier (KM) method, 102 macrophages, 99, 100 metal-backed cup, 99, 100 metal-on-metal (MoM) bearing, 106 osteolysis boxplot, 102, 103 cup inclination angle, 103 mean measurement, 103, 104 patient demographics, 101 production and implantation, 100 radiograph, 106 squeaking, 106 steeper inclination angle, 106 total hip prostheses, 101 treatment algorithm, 106, 107 uncemented hip prostheses, 100 Postel Merle d’Aubigné score, 163 Pseudotumour, 86–87 R Reicher-Jung POLYCUT S microtome, 44 RM Pressfit vitamys implantation, 23, 25 Roman V 1.70 software, linear head penetration, 63 S Sikomet articulation, 121 Sikomet bearing, 119 Soft tissue reactions pseudotumour, 86–87 revision surgery, 87–88 Squeaking ceramic fractures, 133 incidence, 133, 134 influencing factors component orientation, 135 fluid film disruption, 135 patient-related factors, 135–136 prosthetic design and material, 134–135 StatView statistical software, 163 Surgical positioning articular arc angle, 80 cup inclination and negative correlation, 78, 79 femoral diameter, 79 radius, contact patch, 80 wear and metal ion, 78 T Titanium dual-mobility socket cementless fixation, 166 femoral stem loosening or migration, 164

Index intra-prosthetic dislocation, 164, 166 loosening, acetabular cup, 163 low friction coefficient, 167–168 material and method, patients clinical and radiographic examination, 163 etiologies, 162–163 mobile liner, 163 primary hip arthroplasty, 161 StatView statistical software, 163 titanium Novae, 162 mooring screw, 163, 165 Novae® acetabular cup, 165 osteolysis, 163 polyethylene component, 166 Postel Merle d’Aubigné score, 163 prosthetic instability, 161, 167 radiography, THA, 163, 164 wear, 167 Trendelenburg sign, 93 U UHMWPE. See Ultra-high molecular weight polyethylene (UHMWPE) Ultra-high molecular weight polyethylene (UHMWPE). See also Vitamin E-blended UHMWPE acetabular components, 169 cross-linking, 33 fatigue strength, 177 implants accelerated ageing, 24 gamma-sterilised, 26 lifetime, 23 mechanical properties, 26 wear rate, 27, 28 plastic deformation, 169 wear resistance, 60 Uncemented prostheses. See Polyethylene (PE) wear V Visual analogue scale (VAS), 28 Vitamin E-blended UHMWPE biocompatibility, in vitro and in vivo studies machining, 44 results, 50–51 tests and conditions, 44, 45 chemico-physico-mechanical characterisation concentration profile, 49 crystallinity, samples, 43, 46

187 FTIR measurements, 44, 46 IR spectra, accelerated ageing test, 48 non-additivated material, 46, 47 oxidation levels, 47, 48 quantitative amount, ketones concentration, 48, 49 Reicher-Jung POLYCUT S microtome, 44 stress-strain curve, 50 tensile test data, 50 cumulative mass loss, 55 DSC measurements, 53 g-irradiation, 41 GUR, 42 in vivo mechanical stress and oxidation, 42 post-irradiation treatment elimination, 54 samples, disposal, 43 wear test behaviour determination, 44 contact areas, 52 EDTA, 45 liner areas, microscope, 45, 46 rate, non-additivated UHMWPE, 51 servo hydraulic six-station hip simulator, 45 surface damage, 52–54 W Wear and osteolysis reduction, X-PE acetabular osteolysis, 68 duration vs. conventional PE, 67–68 HXLPE, 68 patients and methods ABG-II implant system, 61 assessment, 62 conventional and duration PE, 62 Fisher’s exact test, 63 linear head penetration measurement, 63 polyethylene inserts, 62 unilateral THA, 61 RCTs, 66 results acetabular osteolysis, 65, 66 annual wear rates, 65 patient characteristics and implant parameters, 64 randomization, 64 total linear head penetration vs. duration and conventional PE, 64–65 wear rates, 67 Z Zimmer™ Alloclassic Variall® system, 136, 137