newsletter Contents Features Regulars 2 Where s the Advantage of Ceramic Vs Metal Heads for Contemporary Big Ball XLPE Cups? Prof. I.

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1 newsletter 07 Dec: Issue 2 This Issue: Ceramics The Tribos newsletter is a quarterly publication covering tribological topics and events for orthopaedic surgeons. It is part of a global educational initiative from Stryker. Comments and contributions to the newsletter are welcome and can be ed to tribos@stryker.com. Features Issue 2 focuses on ceramic bearing surfaces in orthopaedics, confronting common issues and concerns such as ceramic bearing fractures, squeaking and edge loading. This edition also includes the biological response of wear particles and an article from Professor Laurent Sedel who has over 30 years of experience with ceramics. Contents Regulars Prof. I.C Clarke Technology Ceramic Bearings Q & A... with Prof. Eileen Ingham from the University of Leeds Your Time Starts Now Dr Harlan C. Amstutz, MD 2 Meeting Report 2007 Tribos Congress - Coolum Australia 15 International Calendar of Events CALL FOR LETTERS Readers are invited to correspond on issues in orthopaedic tribology and on articles in this newsletter Address all letters to: Tribos Newsletter, Xeno Medical, 6 Bramley Business Park, Surrey, GU5 0AZ, UK tribos@stryker.com Fax: +44 (0) Letters must be 200 words or fewer and contain the writer's full name and contact details 2 Where s the Advantage of Ceramic Vs Metal Heads for Contemporary Big Ball XLPE Cups? Prof. I.C Clarke 5 30 Years Experience with all Alumina Bearings in Total Hip Reconstruction Prof. L Sedel 6 Edge Loading Wear and Acoustic Phenomena of Ceramic on Ceramic Bearings Dr W.L Walter Tribos Newsletter _TribosNL.indd 1 27/11/07 8:06:26 PM

2 Meeting Report MEETING REPORT 2007 Tribos Congress Dr Jenny Burke 5 7 July Hyatt Regency Coolum Queensland, Australia Dr Jenny Burke Stryker South Pacific The second Tribos symposium was held in Australia in July this year. The focus of the meeting was to discuss the differences between bearing surfaces from both a scientific and clinical viewpoint. The faculty included experts from Australia, New Zealand, USA and Europe, and the sessions generated healthy discussion and debate. It became evident throughout the meeting just how diverse opinions are between orthopaedic surgeons and how there is no single correct solution for all patients Tribos Congress Australia (from left to right): Dr Aiguo Wang, Dr John Dumbleton, Dr Pat Campbell, Prof Ian Clarke, Mr Peter Devane, Dr Ed Marel (session chair) Where s the Advantage of Ceramic Vs Metal Heads for Contemporary Big Ball XLPE Cups? Prof. Ian C Clarke Professor Ian C Clarke Director of the Howard and Irene Peterson Tribology Laboratory at Loma Linda University (LLU), USA With total hip replacement (THR) experience spanning approximately 40 years, contemporary bearing contenders include metal or ceramic/polyethylene (MPE, CPE), ceramic/ceramic (COC) and metal/metal (MOM) bearings [1, 2]. While cup designs have changed over decades of use, the alumina ceramic and CoCr materials have remained virtually the same. However, the polyethylene bearings have evolved from initially non-crosslinked to moderately crosslinked (XLPE) and now to the highly crosslinked (HXPE) materials [3, 4]. Thus, all contemporary bearing materials offer the claim of high wear resistance, be they MPE, CPE, COC, MOM or even COM combinations [1-4]. What is still unclear is the risk to benefit ratio for each (Fig. 1) and how this may be affected by variables such as manufacturing, design, surgical technique, patient activity and patient longevity. The metal-on-metal (MOM) combination represents the grandfather of THR bearings. Retrieval reports of pioneering MOM designs have generally shown exemplary performance in small sample 2 Tribos Newsletter _TribosNL.indd 2 27/11/07 8:06:30 PM

3 Meeting Report Fig. 1. Comparisons of risks and benefits believed likely to be encountered with MOM, COC and MPE (and CPE) bearings. sets, say N=1 to 12. Advocates claim such MOM bearings (Dia mm) represented superior material choices and excellent clinical performance with minimal wear. Indeed the successful examples were generally well implanted, securely fixed and performed well for over 20 years. In contrast, apparently identical but failed MOM implants were reported to be poorly-made or had been surgically placed with inferior positioning. While the author was in training for PhD in Scotland circa 1970, it was a fact that the once popular MOM bearings, such as McKee-Farrar and Ring THRs, were abandoned in favor of the newly developed, metal-plastic (MPE) types, such as Charnley and Charnley-Muller designs. Why such a sudden demise of the pioneering MOM bearings? One is inevitably left wondering, of the thousands or hundreds of thousands implanted, how many failed during first years in vivo? Today the MOM concept has been revamped in favor of the big-ball concepts (Fig. 1a). Contemporary MOM studies have shown excellent results at 10 years [5, 6]. Unlike UHMWPE THR bearings, the diameter of the MOM bearing does not appear to have been a wear-related issue. While there may be large variations during the Run-in wear phase (0.5-7 mm 3 /million cycles), the long-term, Steadystate wear phase was very low in all simulator studies (< 1 mm 3 /million cycles), regardless of ball diameter (Fig. 2). Nevertheless, virtually every Fig. 2. Comparisons of simulator wear rates with both small and large diameter MOM bearings run under many different test protocols [6]. simulator study has shown some MOM break-away wear phenomenon [2, 6-8]. This triggering of higher MOM wear in simulator studies has not been satisfactorily e x p l a i n e d. Unfortunately, there are also clinical publications demonstrating adverse, short-term results in some MOM series, i.e. lymphocytic reactions, large pseudo-tumors and even osteolysis [9, 10]. Such short-term results were not anticipated, given the laboratory predictions of low MOM wear. It may be that the rigid CoCr bearings offer impingement and 3rd-body wear issues not yet understood. This may provoke adverse 2nd and 3rd body wear effects that were not as critical with UHMWPE bearings [11]? Thus, it is clear that MOM bearings carry some risk of adverse biological effects in the first 5-10 years of both THR and resurfacing designs (Fig. 1a). However, the larger THR and MOM resurfacing designs may offer more protection from the impingement, subluxation and related edge effects of rigid CoCr cups. Ceramic-HXPE bearings represented a significant long-term improvement over MPE bearings and have been generally under appreciated in USA [2]. However only the alumina-alumina bearings (COC) can claim virtually zero biological risk over years of clinical history (Fig. 1b). Nevertheless, with any rigid cup design, there is also a higher risk of COC impingement issues that can result in clicking, squeaking, stripe wear and a small but catastrophic risk of brittle fracture [2, 14-18]. The latest simulator studies of severe stripe wear (Fig. 3) demonstrated still very low wear rates of mm3/million cycles [2, 12, 13] that were also in the clinically relevant range [16-18]. As an Alternate bearing, the alumina ceramic features a ball-diameter limitation due to its need for additional metal-backing and also due to limited ceramic strength. With the high-strength zirconia bearings, an unfortunate clinical experience (Y-TZP ceramic: 1985 to 2000) demonstrated adverse phase transformations that were not predicted by laboratory models [19-21]. Introduction of an alumina-zirconia composite in year 2000 has offered more options for CPE and COC designs [2, 12, 13]. However the issues of COC squeaking and risk of fracture are still being debated today. The MPE bearings of historical significance released millions of polyethylene wear particles for each step the patient made [4]. In sufficient quantities, i.e. wear rates of 80+ mm 3 / year, such debris created adverse biological risks within 10 to 15 years use [1, 2]. It was also known that larger ball sizes increased the risk of osteolysis [Fig. 4a]. However the surgeon would obviously prefer the larger femoral balls to provide both stability and range of motion to his patient s hip joint. Thus the wear resistance of the UHMWPE cups had to be remarkably improved or risk the biological consequences. Compared to non-treated UHMWPE as control, laboratory demonstrations showed that the 3-Mrad irradiation dose produced a 55-65% wear reduction (Fig. 4b). Simulator studies also showed that increasing the radiation dose to 10-Mrad provided a further > 25% wear reduction. Thus the newer HXPE bearings have demonstrated near-zero wear [Fig. 4b], even with large ball diameters. To further improve wear and oxidation resistance while maintaining mechanical properties, manufacturers have developed sequential irradiation/annealing (Stryker X3 TM ), solid-state mechanical deforming processes (Biomet MEP) and vitamin-e enhanced UHMWPE (Biomet, Zimmer E-Poly). Thus is anticipated that the effect of larger femoral heads (Fig. 4a) may be more than offset by the use of highly crosslinked (HXPE) cups (Fig. 4b). The clinical results in first 10 years have been very encouraging [1-4]. However, as Fig. 3. Comparisons of stripe wear produced in simulator run under severe' micro-separation test mode [12, 13]. Narrow stripe wear produced on ceramic ball and rim of cup at 100,000 cycles and then by 5,000,000 cycles duration more extensive stripe wear (Biolox-delta TM ). Tribos Newsletter _TribosNL.indd 3 27/11/07 8:06:31 PM

4 Meeting Report a relatively weak, structural material (Fig. 1c), XLPE and HXPE cups need thicker walls for cemented designs and liner reinforcement by metal shells for non-cemented designs. This limits the MPE ball diameter and there can be the additional risks of backside wear and liner disassociation [1, 2]. Use of larger, metal-backed, cup designs adds further risk of both impingement and 3rd-body abrasive metal wear, particularly when cups may be less protected by bone. Additionally, it is also true that HXPE bearings were more sensitive to abrasive wear conditions. Comparing simulator wear rates with pristine and severely roughened CoCr balls (Ra=500nm), we found no difference in performance between HXPE and XLPE bearings. Thus the role of HXPE, COC and MOM as Alternate bearings continues to be explored, each appearing to have attendant risks and benefits (Fig. 1). Also being considered are hybrid ceramic-on-metal (COM) concepts [22]. Overall, the XLPE and HXPE liners may offer advantages in being more forgiving to insult by 3rd-body wear and lessened impingement issues, i.e. no squeaking. The large-ball MOM offers the unique clinical advantage of improved motion and stability but may trigger adverse biology in some patients. In contrast, COC is the only Alternate bearing to demonstrate lack of adverse biology over years of use. However ceramics have attendant design limitations and some small risk of fracture. Overall such continued refinements in design, materials selection and cup navigation features will surely offer considerable benefit to the younger patients now undergoing THR procedures. Fig. 4a. Volumetric wear of XLPE cups generally increased approx. 10% per 1mm of diameter increase [2]. Fig. 4b. Volumetric wear of XLPE cups generally decreased approx. 95% with crosslinked by radiation to 100kGy [4]. REFERENCES 1) McKellop HA. Assessment of wear of materials for artificial joints. In J. Callaghan, A Rosenberg and H. Rubash Eds. The Adult Hip. NY Lippencott- Raven, p , ) Clarke IC, Donaldson TK and Jobe C. Total Joint Replacement - Effects of Materials and Designs on Osteolysis. In J. Garino Eds., Adult Reconstruction and Arthroplasty - Core Knowledge in Orthopaedics, Chpt. 1, ) Williams P. and Clarke IC. Total Wear Performance of UHMWPE Fabrication Methods in a Hip Simulator Model. In ORS, 2007, San Diego, California. 4) Williams P, Yamamoto, K, Oonishi H and Clarke IC. Highly crossslinked polyethylenes. In Tribology Transactions 50, , ) Dorr LD, Zhinian W, Longjohn DB, Dubois B and Murken R. Total hip arthroplasty with use of the Metasul metal-on-metal articulation. J. Bone Joint Surg. 82A: , ) Clarke IC, Donaldson TK, Bowsher JG et al. Current Concepts of metal-onmetal hip resurfacing. Orthop. Clin. North Am. 36, 143, ) Bowsher JG, Donaldson TK, Wang A, Essner A and Clarke IC. Low running-in wear for large diameter metal-on-metal hip bearings. In ORS, 2007, San Diego, California. 8) Bowsher JG, Donaldson TK, and Clarke IC. The Relationship between wear and ion release for large diameter metal-on-metal hip bearings. In Biomaterials Soc., Chicago, Illinois, ) Milosev I, Trebse R. Kovac S, Cor A and Pisot V. Survivorship and retrieval analysis of Sikomet metal-on-metal total hip replacements at a mean of seven years. J. Bone Jt. Surg. 88A, , ) Korovessis P, Petsinis G, Repanti M and Repantis T. Metallosis after contemporary metal-on-metal total hip arthroplasty 5 to 9 year follow-up. J. Bone Jt. Surg. 88A, , ) Ishida, T, Clarke, IC, Shirasu T, Shishido T, Yamamoto K and Lazennec J-Y. Detailed Wear Mapping of Retrieved Second-Generation Metal-on-Metal THR. In ORS, San Diego, California, ) Clarke IC, Donaldson, TK, Pezzotti, P, Green, D. and Williams, PA. Status of Aluminum, Oxinium, Zirconia ad Zirconia-toughened Alumina Hip Implants in USA. In AAOS Scientific Exhibit, San Diego, California, ) Green, D, Williams P, Pezzotti, G and Clarke, IC. Stripe Wear Analyses in Large Diameter Ceramic-on-Ceramic Bearings in Microseparation Simulator Mode. In Biomaterials Soc., Chicago, Illinois, ) Manaka M, Clarke IC, Yamamoto K, Shishido T, Gustafson A, and Imakiire A. Stripe wear rates in alumina THR - Comparison of microseparation simulator study with retrieved implants. J. Biomed Mater. Res. (B); 69: , ) Shishido T, Yamamoto K, Tanaka S, Masaoka T, Clarke I and Williams PA. A study of a retrieved implant of ceramic-on-ceramic total hip arthroplasty. J. Arthroplasty;21: , ) Walter WL, Insley GM, Walter WK and Tuke MA. Edge loading in third generation alumina ceramic-on-ceramic bearings: Stripe wear. J. Arthroplasty; 19: , ) Walter WL, Lusty PJ, Watson A, O'Toole G, Tuke MA, Zicat B and Walter WK. Stripe wear and squeaking in ceramic total hip bearings. Seminars in Arthroplasty; 17: , ) Walter WL, O'Toole GC, Walter WK, Ellis A and Zicat BA. Squeaking in Ceramic-on-Ceramic Hips - The importance of acetabular component orientation. J. Arthroplasty; 22: , ) Clarke IC. Metastable Nature of Zirconia Femoral Heads From a 20-Year Perspective of Clinical and Simulator Wear Study. Seminars in Arthroplasty, Volume 17, , ) Brown S, Green D, Pezzotti G, Donaldson TK, Clarke IC. Possible Triggers for Phase Transformation in Zirconia Hip Balls. J. Biomedical Materials Res. (B), accepted March ) Donaldson, TD, Clarke IC, Pezzotti, G, Green D, Brown, S, Ries, MD. Williams, PA. In AAOS Scientific Exhibit: Status of Zirconia Hip and Knee Implants in USA, San Diego, California, ) Ishida, T, Clarke, IC, Donaldson, TK Shirasu H, and Yamamoto K. Ceramic-on- Metal Simulator Wear and Ion Comparisons: 32mm vs. 38mm Diameters. In 53rd ORS, San Diego, California, Tribos Newsletter _TribosNL.indd 4 27/11/07 8:06:34 PM

5 Meeting Report 30 Years Experience with Alumina on Alumina Bearings in Total Hip Reconstruction Prof. Laurent Sedel Professor Laurent Sedel University of Paris 7 Denis Diderot, Hôpital Lariboisière, Assistance Publique Hôpitaux de Paris All alumina bearings were introduced in 1970 to address the problem of polyethylene wear debris generated by metal on polyethylene bearing combinations, and to avoid possible general or local biological problems due to ion release with metal on metal cobalt chromium molybdenum alloy combinations 1. At the moment ceramic on ceramic bearings appear to be a real break through even if evidence based materials of Level 1 are not available at the moment. FDA driven studies are on the way but currently only short term data is available. Within the early days of using ceramic on ceramic bearings, surgeons experienced important learning curves coping with manufacturers utilising sub-optimal materials, deficient surgical techniques and product design problems. It is difficult to produce medical grade alumina as it is an extremely hard and rigid material. It is manufactured from a powder that is compressed in a mould at a very high temperature 2. Alumina s modulus of elasticity is about 300 GPa and is so hard that it can be scratched only by itself or by diamond. Its tribological properties are excellent if adequate clearance between the head and cup is obtained during manufacturing and after implantation; this influences the lubrication mode and both boundary lubrication and fluid film has been described 3. Ceramic on ceramic bearings have a very low coefficient of friction and the most interesting quality is its low debris generation. In general, linear wear is about 1 μm depth per year on the head 4,5. In some situations tilting of the component after loosening, edge-loading due to biomechanical abnormalities or to excessive anteversion/ inclination, and wear debris production may be markedly increased; this has been described as stripe wear 5. This increased wear is still far below the amount of regular wear debris produced by metal on polyethylene materials. Ceramic fracture is still of concern but crack propagation will not be observed if quality material and optimal design are obtained. Clinical Results In every series reported from our group or others, the most pre-eminent result is the lack of osteolysis. Socket fixation was a problem for many years resulting in mechanical loosening but with the introduction of press-fit metal backed alumina cups 18 years ago, this problem has been resolved. The most recent results depicted 98% survivorship at 10 years with this design. At the moment alumina on alumina appears to provide the best answer to wear and osteolysis and it is particularly dedicated to young and active patients. REFERENCES 1 Blood and urine metal ion levels in young and active patients after Birmingham hip resurfacing arthroplasty., Vendittoli PA, Ganapathi M, Lavigne M., J Bone Joint Surg Br., 89(7):989; Jul Handbook of properties of technical & engineering ceramics: part 1 and 2, R Morrell, HMSO, 1985, isbn Books 3 Effect of swing phase load on metal-on-metal hip lubrication, friction and wear. Williams S, Jalali-Vahid D, Brockett C, Jin Z, Stone MH, Ingham E, Fisher J., J Biomech., 39(12): , Epub 2005, Sep 6. 4 H McKellop, Bearing surfaces in total hip replacements: state of the art and future developments., Instr Course Lect., 50:165-79, The influence of acetabular cup angle on the wear of "BIOLOX Forte" alumina ceramic bearing couples in a hip joint simulator. Nevelos JE, Ingham E, Doyle C, Nevelos AB, Fisher J. J Mater Sci Mater Med., 12(2):141-4., Feb 2001 Original Cemented Ceraver Osteal Ceramic on Ceramic Hip More Recent Hybrid Cemented Stem and Cementless Socket Ceraver Osteal Ceramic Hip Tribos Newsletter _TribosNL.indd 5 27/11/07 8:06:35 PM

6 Meeting Report Edge Loading, Wear and Acoustic Phenomena in Ceramic on Ceramic Bearings Dr Bill L Walter Dr Bill L Walter Sydney Northside Hip & Knee Surgeons, Sydney, Australia Alumina ceramic-on-ceramic bearings provide an answer to the osteolysis seen with traditional metal-on-polyethylene bearings. However this new bearing has had in vivo reports of edge loading wear and squeaking which was not predicted from in vitro studies. The three investigations below shed some light onto these phenomena. 1. We studied 33 bearings retrieved from cementless hip arthroplasties after more than 6 months in service with third generation alumina ceramic-on-ceramic bearings. Wear volume was measured with a Roundtest machine. Acetabular orientation was measured from the anteroposterior pelvic radiograph. The median early wear rate overall was 0.1mm 3 per year, from the heads and 0.04mm 3 per year from the liners. We excluded hips where the components had migrated. In this subgroup of 22 bearings, those with acetabular anteversion of less than 15 degrees (seven femoral heads) had a median femoral head wear rate of 1.2 mm 3 a year, compared to 0mm 3 from those with anteversion of 15 degrees or more (15 femoral heads, p <0.001). Even under edge loading, wear volumes with ceramic-on-ceramic bearings are small in comparison with other bearing materials. Low acetabular anteversion is associated with greater wear. 2. We also reviewed seventeen patients who complained of a squeaking hip arthoplasty and matched them to 17 controls comparing acetabular component orientation. Ninety four percent of control hips were in an ideal range of 25 ± 10 anteversion and 45 ± 10 inclination but only 35% of squeaking hips were in this range (p=0.0003). Eight hips squeak with bending. Four hips squeak with walking and 5 hips squeak after prolonged periods of walking. Hips that squeaked with walking had acetabular components that were more anteverted (40 ) than hips that squeaked with bending (19 ) (p=0.001) or prolonged walking (18 ) (p=0.020). The hips started squeaking after an average of 14 months. Patients with squeaking hips were younger, heavier and taller than patients with silent hips. 3. We analyzed 12 alumina ceramic-on-ceramic bearings from squeaking hips collected at revision surgery after an average of 23 months in service (11 to 61 months). There were 4 different designs of acetabular component from 2 different manufacturers. Eleven have an elevated metal rim which is proud of the ceramic and one does not. All 12 bearings showed evidence of edge loading wear. Mean femoral head wear volume was 2.9 mm 3 per year. Seven of the 12 implants also had evidence of impingement of the femoral neck against the elevated metallic rim or the ceramic insert or both. There was no chipping or fracture of any of the ceramic components. This patient s hip squeaked when she bent forward. There is no impingement of the titanium neck against the rim of the cup but there is evidence of edge loading of the ceramic femoral head against the rim of the ceramic insert (coloured with a blue pen). Squeaking is a rare complication of hard-onhard hip bearings. Occasionally the noise is troublesome enough to warrant revision surgery. Although impingement seems to be present in the majority of cases it does not seem to be necessary. Edge loading wear was the common factor in all cases and this may prove to be a critical mechanism. Edge loading and squeaking are related to abnormal loading of the bearing which is influenced by patient factors, surgical factors and implant design factors. 6 Tribos Newsletter _TribosNL.indd 6 27/11/07 8:06:36 PM

7 Technology TECHNOLOGY Ceramic Technology In Orthopaedics Prof. Besim Ben-Nissan and Dr Jenny Burke Professor Besim Ben-Nissan University of Technology Sydney, Australia Dr Jenny Burke Stryker South Pacific, Australia INTRODUCTION Aluminium oxide (Al 2O 3), more commonly known as alumina is the most widely used oxide ceramic material. As a raw material, Al 2O 3 powder is produced in large quantities from the mineral bauxite, by the Bayer process. Its applications are widespread in engineering and biomedical applications. Some common examples include spark plugs, tap washers, pump seals, electronic substrates, grinding media, abrasion-resistant tiles, cutting tools, bioceramics, orthopaedic and dental applications, body armour, laboratory ware and wear parts for the textile and paper industries. High-purity alumina is normally classified as that with a purity of 99.99% and has been developed as an alternative to surgical metal alloys for orthopaedic and dental applications such as total hip replacement. Due to its high hardness, low friction and excellent wear and corrosion resistance, alumina is suitable to be used as articulating surfaces in orthopaedic applications. the fact that ceramics are hydrophilic with good wettability (Figure 1) and can be highly polished, which provides a superior load bearing surface with itself or against polymeric materials in a physiologic environment. The mechanical behaviour of alumina ceramics in simulated physiological environments has led to long-term survival predictions when To achieve the long-term stability of alumina in orthopaedic applications, the material must have extremely low porosity, and its microstructure must be fine and homogenous. Medical-grade alumina has a very low concentration of sintering subjected to sub-critical stresses. The stress magnitude of medical-grade alumina was estimated to be 112 MPa for a 50-year period with a 99.9% survival probability (Ben-Nissan, 1993). additives, very small grain size (<1 micron), and a narrow grain-size distribution. Such a microstructure is capable of resisting static fatigue and slow crack growth while the ceramic is under load. Recently, Alumina Matrix Composites were selected as the best new family of ceramics to provide the foundation for an expanded Figure 1. The wettability of bearings materials in orthopaedics. The lower angle indicates that the material is hydrophilic and a higher angle indicates that use of ceramics in the material is hydrophobic. orthopaedics. CLINICAL EXPERIENCE The German Standards Institute (DIN) As the last 30 years have shown, alumina published the first recognized requirements for can be reliably used for ceramic femoral alumina in orthopaedics in 1979 as DIN heads. In work carried out by Oonishi et al. This standard was adopted in 1981 by the International Standards Organization (ISO) as ISO 6474 and in 1983 by the American Society for Testing and Materials (ASTM) as ASTM F603. (2003), the authors have reported that in total hip arthroplasty (THA) a decrease in wear by 25 30% was noted when comparing aluminaon-ultra high molecular weight polyethylene (UHMWPE) to that of metal-on-uhmwpe in hip simulator tests and clinical results. Wear of THA Ceramics are brittle materials with relatively poor tensile properties. However, they have excellent compressive strength, high resistance to wear when using alumina-on-alumina was observed to be near zero in a similar hip simulator test (Sedel, 1999). and low frictional properties in articulation. These low frictional properties are enhanced by Alumina-on-alumina bearings in total hip Tribos Newsletter _TribosNL.indd 7 27/11/07 8:06:38 PM

8 Technology replacements have been successfully used since the early1970s. Since its initiation by Boutin et al. (1988), more than 2.5 million femoral heads and nearly 100,000 liners have been implanted world-wide. It can be conditionally stated that alumina possesses excellent tribologic properties and its extra low wear debris generation could, in theory, provide an answer to osteolysis. engineered with substantially improved mechanical properties so that new applications, such as spine and knee components, as well as larger and thinner versions of existing components are now possible. Both of these materials can be used either articulating against polyethylene, or against each other. Table 1 lists the physical and mechanical properties of the Biolox products. In the 1990s, Professor Willmann suggested that the success rate of the alumina rests on the use of femoral heads larger than 28 mm in diameter. Several in vitro and in vivo studies using larger than 28 mm femoral heads demonstrated the advantage of using alumina-on-alumina bearings in young patients, and patients with high-demand activity (Willmann, 2000). Biolox Delta is stronger than Biolox Forte. However, it is worth mentioning that it is the loads applied to the components that determine their service life no matter what the strength of the material may be. The magnitude of these loads and the resulting stresses depend to a large extent on the product geometry, the design of the entire implant system, the surgical technique and the post-operative behaviour of the patient. CERAMIC MATERIAL SUPPLIERS High-purity alumina bioceramics are currently commercially available from various manufacturers. The following companies are the main suppliers to the medical industry: Morgan Advanced Ceramics (MAC) (Worcestershire, UK) began manufacturing orthopaedic devices in 1985 and quickly became a recognised supplier of ceramic femoral heads for hip replacements. MAC Bioceramics has one of the longest clinical history for alumina ceramic materials, HIP Vitox alumina since Property Biolox Delta Biolox Forte Density (g/cm3) > Young s Modulus (GPa) Flexural Strength (MPa) 1203 ± ± 106 Fracture Toughness (Mpam1/2) Hardness (HV) 1840 ± ± 60 Grain size (μm) Table 1. The physical and mechanical properties of Biolox Delta and Forte (CeramTec) MANUFACTURING IMPROVEMENTS Ceramics are manufactured from the consolidation of fine powders. Improvement in the manufacturing process, such as the use of hot isostatic pressing has resulted in the higher densities and small grain structures required by these bioceramics. These manufacturing processes permit the achievement of a near theoretical 100% density and a very fine grain structure with the addition of appropriate sintering aids. This results in optimization of strength and reduces the risk of crack propagation and component fracture (Sedel et al, 2007). CONCLUSIONS The tribological properties of alumina ceramic against itself are outstanding; with a linear wear rate 4000 times lower than that of metalon-polyethylene. These properties, which have been demonstrated both in vitro and from the analysis of retrieved implants, are responsible for the limited amount of wear particles produced and the subsequent moderate biological reaction to ceramic wear debris. The clinical and radiologic longterm results with alumina-on-alumina are expected to show exceptionally long-term survival in patients with high physical demands. The Kyocera Corporation was founded in 1959 as a producer of fine ceramics. By combining these engineered materials with metals and plastics, and integrating them with other technologies, Kyocera Corporation has become a leading supplier of engineered ceramics, semiconductor packages, electronic components, solar energy systems, medical and dental implants, telecommunications equipment, and document solutions equipment. CeramTec combines over 100 years of experience stemming from a number of innovative companies which have always been among the leaders in the field of high-performance ceramics. CeramTec is active in the biomedical field, electronics, electrical engineering, hermetic systems, piezo-technology, medical technology, mechanical systems, chemicals, textiles, industrial equipment, machining or metal cutting, and many other segments. Two different medical grade materials are manufactured by CeramTec; Biolox Forte is a pure alumina material which has been the backbone of CeramTec s product and readily available for many years. Biolox Delta is an alumina matrix composite material that has been specifically REFERENCES Ben-Nissan B (1993), Review: reliability and finite element analysis in ceramic engineering design, Mater Forum, 17, Boutin P, Christel P, Dorlot J M, Meunier A, de Roquancourt A, Blanquaert D, Herman S, Sedel L and Witvoet J (1988), The Use of Dense Alumina- Alumina Ceramic Combination in Total Hip Replacement, J Biomed Mater Res, 22, Oonishi H, Clarke I C, Good V, Amino H, Ueno M, Masuda S, Oomamiuda K, Ishimaru H, Yamamoto M and Tsuji E (2003), Needs of Bioceramics to Longevity of Total Joint Arthroplasty, in Ben-Nissan B, Sher D and Walsh W, Bioceramics 15, Switzerland, Trans. Tech. Publications, Sedel L (1999), Tribology and Clinical Experience of Alumina-Alumina Articulations, in Proceeding of the 66th Annual Meeting of the American Academy of Orthopaedic Surgeons, Anaheim, CA., February 4-8, 120. Sedel L and Raould A (2007), Engineering aspect of alumina on alumina hip prosthesis, Proc. IMechE Vol. 221 Part H: J. Engineering in Medicine Willmann G (2000), Experience on zirconia ceramic femoral head, in Zirconia femoral heads for total hip prostheses, 6th world biomaterial congress workshops, Hawaii, USA. 8 Tribos Newsletter _TribosNL.indd 8 27/11/07 8:06:38 PM

9 Technology FIVE FACTS ABOUT (P. Boutin et al, The use of dense alumina-alumina ceramic combination in CERAMICS total hip replacement, Journal of Biomaterials Research, Vol 22: , 1988) 1. Precious ruby and sapphire gems are large, single, perfect crystals of BIOLOX forte was introduced into the market in A total of 1,984,949 aluminium oxide (alumina) with traces of other metals that give them their 4. colour. BIOLOX forte alumina THA bearing components were manufactured from January 2000 to December Based on the clinical reports received by the The word ceramic can be traced back to the Greek term keramos, manufacturer, a fractured bearing rate of 0.020% occurred. The overall probability meaning a potter or pottery. Keramos in turn is related to an older Sanskrit of a BIOLOX forte alumina component failure in vivo was therefore about 2 in 10,000 root meaning to burn. Thus the early Greeks used the term to mean burned (J. Garino, M. N. Rahaman, and B. S. Bal, The Reliability of Modern Alumina stuff or burned earth when referring to products obtained through the action Bearings in Total Hip Arthroplasty, Semin Arthroplasty, Vol 17: , of fire upon earthy materials. 2006) Pierre Boutin implanted the first ceramic on ceramic hip in France in 5. Alumina is so strong in compression that an average 5000 kg African The bearing was 32mm in diameter and manufactured from aluminium elephant could stand on a 28mm liner without it cracking. However, the material oxide (alumina) ceramic. is not able to readily plastically deform so cannot absorb shock loading and The implant lasted 17 years until the patient died and wear was virtually non-existent in the retrieved ceramic implant. bending so easily. Long-term Clinical Results for Ceramic-on-Ceramic Bearings Michael Manley Ph.D., James D Antonio M.D., William Capello M.D. (from left to right): William N. Capello M.D. M.D., Indiana Univ. Medical Center, Dept. of Orthopaedic Surgery, Indianapolis, USA Michael Manley Ph.D. Academic Director, Homer Stryker Center for Orthopaedic Education, Mahwah, USA James A.D Antonio M.D. Greater Pittsburg Orthopaedics Assoc., Pennsylvania, USA INTRODUCTION Over the past four decades total hip replacement arthroplasty has evolved to become one of the most durable and successful treatments in medicine1. Long term clinical studies show that when revision is required, one of the causes of failure has been bearing wear and osteolytic changes in supporting bony structures2, 3. The literature suggests that there is a direct correlation between the wear rate of historic polyethylene bearings and the presence or absence of osteolysis4-7 In recent decades younger and more active patients have been receiving total hips arthroplasty8, which has led to development of new bearing surfaces with improved wear properties. Three alternative bearings to metal-on-conventional polyethylene have become available during the past decade: metal- or ceramic-on-highly crosslinked polyethylene, metal/metal, and alumina ceramic-on-alumina ceramic. Of these, alumina ceramic bearings have many potential advantages. They are very hard and scratch resistant, have a lower coefficient of friction and superior wear resistance to the alternatives, and have excellent lubrication properties as they are more hydrophilic than either polyethylene or metal. Alumina ceramic bearings have been in use for several decades9. First generation bearings performed poorly in the 1970 s and 1980 s due to poor mechanical properties and early failures. Contemporary alumina ceramics are of higher quality and have addressed many of these concerns. With the potential for low wear and excellent host response, we conducted a prospective clinical study to compare contemporary alumina ceramic bearings with cobalt chromium (CoCr)/conventional polyethylene bearings. The most recent data from that study are reported here. Tribos Newsletter _TribosNL.indd /11/07 8:06:39 PM

10 Meeting Technology Report MATERIALS AND METHODS In October 1996, a US IDE (Investigational Device Exemption) prospective controlled study began in which alumina / alumina ceramic bearings or CoCr / polyethylene bearings were implanted in a randomized fashion in a cohort of patients undergoing total hip replacement. Twenty-two investigators at sixteen sites implanted 514 hips in 458 patients. All sites received approval from their Institutional Review board and all patients signed an informed consent agreement. All patients received the same femoral stem (Omnifit-HA, Stryker Howmedica- Osteonics, Mahwah, NJ, USA) and one of three bearing/acetabular component combinations assigned randomly. System I was an ABC ceramic/ceramic bearing and a porous-coated titanium shell, System II an ABC ceramic/ceramic bearing and an arc deposited titanium shell with HA coating and System III a CoCr/ conventional polyethylene bearing and a porous-coated titanium shell. System III was the study control. On completion of the FDA study requirement (2 years minimum follow-up), five surgeons responsible for 278 patients with 289 hips agreed to follow these patients for the long-term. On completion of the ABC study, six surgeons at six institutions proceeded with Phase 2 of the evaluation as a fourth (Trident ) arm. The Trident design has the ceramic acetabular insert preassembled in a shrink-fit titanium sleeve. This titanium sleeve protects the rim of the ceramic from intra-operative chipping and increases the burst strength of the alumina ceramic construct. The Trident arm began in September Again, on completion of the FDA requirement, five surgeons agreed Figure 1: Kaplan-Meier survivorship endpoint revision for any reason: 6-yr and 9-yr survivorship for ABC and 6-yr survivorship for Trident. to follow186 Trident hips in 174 patients for a minimum of ten years. Results reported here are for the five to nine-year ABC clinical follow-up and the four to six-year Trident clinical results. ABC I (N=75) Clinical complications included two post operative ceramic insert fractures, one in ABC System II and one in the Trident group. The System II insert was revised 9 years postoperatively secondary to pain. Visible ABC II (N=68) Trident (N=164) Control (N=71) Pain none/slight 97% 94% 93% 91% Limp none/mild 100% 99% 98% 97% Mean Harris Score Harris % G/E 96% 94% 95% 97% Pt. Satisfaction (Are you satisfied with results?) 100% 99% 99% 99% TABLE I: Clinical Data: Latest evaluation (ABC minimum 6-year follow-up: Trident minimum 4-year follow-up) Mid-term results suggest that ceramic bearings release less debris clinically than conventional polyethylene. RESULTS Three chips (1.5%) occurred in the ABC alumina ceramic study group at the time of liner insertion and the alumina ceramic liner and/ or shell was replaced at the time of surgery. No complications related to these events were reported. No intra-operative chips were reported with Trident. Long-term results of the ABC and Trident systems are excellent. Clinical data for the ABC and Trident Systems are listed in Table I, major orthopaedic complications are shown in Table II. The survivorship for ceramic bearings was significantly higher than for the metal-on-polyethylene control System III (p=0.0201) (Figure 1). ceramic debris was noticeable on radiographic evaluation. The Trident insert was revised 6.5 years postoperatively due to fracture of the ceramic liner. Radiographic analysis of all implants showed appearance of a small lesion (scalloping) at the femoral neck resection level in some patients. This is believed to a lytic lesion resulting from the release of bearing debris (Figure 2). This phenomena was recorded in 3 of 194 ceramic/ ceramic ABC I and II bearings (1.5%), in one of 186 Trident bearings (0.5%), and in 19 of 95 CoCr / polyethylene bearing controls (20%). The difference in presence of the lesion between the ceramic bearings and the controls 10 Tribos Newsletter _TribosNL.indd 10 27/11/07 8:06:39 PM

11 Meeting Technology Report Figure 2: Mid-term follow-up of a ceramic-onceramic bearing (left) and CoCr-on-polyethylene bearing (right). A region of reduced radiographic density at the femoral resection level (scalloping) is clearly seen with the polyethylene bearing and is almost certainly a reaction to bearing debris. was statistically significant (p=0.001). One patient with an ABC System II bearing and neck scalloping in Zone 14 was asymptomatic at latest (7-year) follow-up. Three patients who received either an ABC or Trident bearing (3 hips, 0.8%) reported intermittent squeaking of their hips with activities of daily living. This incidence of squeaking is similar to that reported by Walter et al 10 (13 of 2397 hips, 0.5%). SUMMARY The most common mode of long-term failure for total hip arthroplasty is aseptic loosening. It has Complication ABC System I been recognized that particulate debris is one cause of the inflammatory response that leads to bone resorption and loosening of the implants over time. Eliminating wear debris may help extend implant life. Our radiographic methods use an indirect assessment of debris release by looking for changes in radiographic density of small lesions at the resection level of the femur. Mid-term results suggest that ceramic bearings release less debris clinically than conventional polyethylene. This finding, together with the excellent clinical and survivorship data associated with the ceramic bearings in this study, suggests that alumina ceramic/ceramic bearings can be recommended for young and active patients. ABC System II Trident Control Revision-Acetabular (2.1%) Revision-Femoral 1 (1.0%) 1 (1.1%) 0 2 (2.1%) Revision-all 1(1.0%) 1 (1.1%) 0 1 (1.1%) Revision-Insert and/or head only Intra op Femoral Fx/ Crack 0 2 (2.1%) 4 (2.2%) 4 (4.2%) 6 (6.1%) 5 (5.3%) 4 (2.2%) 4 (4.2%) Post Op Femoral Fx. 4 (4.0%) 1 (1.1%) 0 1 (1.1%) Dislocation 2 (2.0%) 1 (1.1%) 4 (2.2%) 5 (5.3%) REFERENCES 1. Papatheofanis, F. Technology Report: Prosthetic Hip and Knee Arthroplasty. In: University Hospital Consortium (UHC) Technology Advancement Center Holt, G., C. Murnaghan, J. Reilly, and R.M. Meek, The biology of aseptic osteolysis. Clin Orthop Relat Res, : p Parvisi, J., F.A. Wade, V. Rapuri, B.D. Springer, D.J. Berry, and W.J. Hozack, Revision hip athroplasty for late instability secondary to polyethylene wear. Clin Orthop Relat Res, : p NIH, C.S., National Institutes of Health Consensus Paper on Total Hip Replacement (5): p Saikko, V.O., P.O. Paavolainen, and P.S. Slatis, Wear of the polyethylene acetabular cup, metallic and ceramic heads compared in a hip simulator. Acta Orthop Scand, (4): p Harris, W.H., Osteolysis and particle disease in hip replacement. Acta Orthop Scand, (1): p Geesink, R. and N. Hoefnagels, Six-year results of hydroxyapatite-coated total hip replacement. J Bone Joint Surg Br, (4): p Capello, W.N., J.A. D'Antonio, J.R. Feinberg, and M.T. Manley, Hydroxyapatite-coated total hip femoral components in patients less than fifty years old. Clinical and radiographic results after five to eight years of follow-up. J Bone Joint Surg Am, (7): p Sedel, L., R. Nizard, P. Bizot, and A. Meunier, Perspective on a 20-year experience with cermic-on-ceramic articulation intotal hip replacement. Seminars in Arthroplasty, : p Walter, W.L., G.C. O'Toole, W.K. Walter, A. Ellis, and B.A. Zicat, Squeaking in ceramic-onceramic hips - The importance of acetabular component orientation. J Arthroplasty, (4): p Heterotopic Bone 6 (6.1%) 7 (7.4%) 10 (5.4%) 11 (11.6%) Intra Op Insert Chip 2 (2.0%) 1 (1.1%) 0 0 Post Op Insert Fx. 0 1 (1.1%) 1 (0.5%) 0 TABLE II: Complications Tribos Newsletter _TribosNL.indd 11 27/11/07 8:06:39 PM

12 Q & A Q & A: CERAMIC ON CERAMIC WEAR DEBRIS Professor Eileen Ingham University of Leeds, UK Dr Jim Nevelos Stryker EMEA, Hambridge Road, Newbury, UK Send in your tribology questions! An expert will answer your bearing surface queries. questions to tribos@stryker.com If we select your question for the Q & A section of the newsletter, we will notify you prior to printing. Following on from last issue s interview with Dr Andrew Shimmin, Professor Eileen Ingham from the University of Leeds kindly agreed to answer some questions about wear debris in general and also on the specifics of ceramic on ceramic wear debris. Professor Ingham s microbiology research group has published some of the landmark papers in the field of cellular reactions to wear debris including a lot of work on ceramic on ceramic. The conventional wisdom holds that polyethylene wear debris causes osteolysis whereas ceramic wear debris is completely inert. To explore this and other issues, the following questions were posed by Jim Nevelos, a European Tribos TM faculty member: 1. According to the conventional wisdom, polyethylene wear debris causes osteolysis. Is the relationship between wear and lysis a straightforward one, i.e. is it a straight relationship with volume or a combination of volume and debris size? Several authors reported on the relationship between wear of the UHMWPE acetabular cup and osteolysis during the mid-1990`s. Dowd et al (J. Bone & Joint Surgery 2000; 82A: 1102) reported on the relationship between an increase in penetration rate and the occurrence of osteolysis 10 years following implantation with all patients with an average penetration rate of greater than 0.3mm per year showing radiographic evidence of osteolysis. In these studies, however the UHMWPE would have been the historical material and gamma irradiated in air, giving reasonably consistent results in different series. Based upon years of studying clinically relevant UHMWPE particle interactions with macrophages in vitro, I strongly believe that it is the volumetric concentration in the submicrometre size range that is critical. If you challenge primary human macrophages with endotoxin-free particles of UHMWPE in different size ranges at the same volumetric concentration, particles in the size range micrometre will activate the macrophages to produce osteolytic cytokines such as TNFalpha and bone resorbing activity. Particles larger or smaller than this evoke much less of a response, with particles above 10 micrometres evoking no measurable response with macrophages from most individuals. In fact, if you challenge macrophages with a mixture of different size particles, the level of response can be directly related to the volumetric proportion of submicrometre particles in the mixture. 2. Is there a difference in the response between patients? Again, I have to refer to in vitro data to answer this question. In our in vitro studies, we have found a marked difference in the levels of osteolytic cytokines (TNF-alpha, IL-1 beta and IL-6) produced by macrophages from different donors in response to the same volume and size range of UHMWPE particles. The pattern of response is always similar, with the submicrometre sized particles evoking the greatest response, but the concentration of given cytokine released can vary by a factor of ten. I believe that this is due to genetic polymorphisms in cytokine promoter genes. The biological variation in the population leads to some high responders, some low responders and the norm. This is something that one of my colleagues, Dr. Tipper is currently investigating in a long term study. 3. Ceramic on ceramic wear debris is generally held to be tiny in size and in volume and totally inert. Is this really the case? We have studied the size of alumina ceramic wear particles generated in vivo (by investigation of retrieved tissues) and in vitro (by isolating the particles from hip joint simulations). The particles generated in vivo have a mode size of 10 nanometres but larger particles (100 nanometres - 3 micrometres) are also produced. When alumina ceramic hips are worn in hip simulators under standard 12 Tribos Newsletter _TribosNL.indd 12 27/11/07 8:06:40 PM

13 Q & A conditions (normal walking cycle) only the nanometre sized particles are produced. In order to generate the larger particles seen in tissues from patients, we have run our hip simulators with microseparation between the head and cup, which gives repeated contact of the head on the rim of the cup. This replicates the particle sizes seen in vivo. Hence, we believe that under normal wear, the particles are in the nanometre sized range and that some larger particles are generated when you get contact of the head on the rim of the cup. Ceramic on ceramic bearings are extremely low wearing, with wear rates 50 times less than moderately cross-linked polyethylene even when tested under severe microseparation conditions. In terms of their biological activity, alumina ceramic particles generated in laboratory simulations evoke very little response in macrophages. We have tested the particles generated under microseparation conditions for their capacity to activate macrophages in vitro and found that they will only induce a response at massively high concentrations of 500 μm 3 per cell. This is in comparison to UHMWPE particles which activate macrophages at μm 3 per cell. 4. Genetic damage is often discussed around metal on metal bearings and yet there is one report of DNA damage around ceramic on ceramic hips. Is this a real concern or an artefact? Very high volumetric concentrations of alumina ceramic particles are toxic to cells. Hence, it is conceivable that with the accumulation of very high concentrations of ceramic particles in cells, there may be sub-lethal DNA damage that is not repaired. Of course, with ceramic on ceramic bearings there is the potential for metal particles/ions to be present in the tissues as a result of fretting wear of the stem and modular junctions. The advantage of ceramics over current plastics is the combination of low wear volume and nanometre sized particles which appear to be less able to evoke osteolytic cytokine release from macrophages than larger particles in the phagocytosible size range. Are ceramics the ultimate in terms of inert debris? I am a scientist and never try to predict the future! RECENT PUBLISHED PAPERS ON CERAMICS Ha, Y. C., K. H. Koo, et al. (2007). "Cementless alumina-on-alumina total hip arthroplasty in patients younger than 50 years: a 5-year minimum follow-up study." J Arthroplasty 22(2): Hwang, D. S., Y. M. Kim, et al. (2007). "Alumina femoral head fracture in uncemented total hip arthroplasty with a ceramic sandwich cup." J Arthroplasty 22(3): Kim, Y. H., S. H. Yoon, et al. (2007). "Changes in the bone mineral density in the acetabulum and proximal femur after cementless total hip replacement: alumina-on-alumina versus alumina-on-polyethylene articulation." J Bone Joint Surg Br 89(2): Kohn, D. and D. Pape (2007). "Extensive intrapelvic granuloma formation caused by ceramic fragments after revision total hip arthroplasty." J Arthroplasty 22(2): You have experience in analysing tissues from all types of hip replacements, how do the tissues differ in typical ceramic on ceramic cases from typical metal on polyethylene cases? The tissues retrieved from typical failed metal-on-polyethylene hips show a characteristic granulomatous reaction involving a dense macrophage infiltrate and the presence of giant cells. It is possible to visualise the large particles of polyethylene within macrophages and giant cells. In contrast, the tissues from around failed alumina ceramic prostheses that I have looked at had a mixed pathology with areas of healthy fibrous tissue, some areas rich in macrophages and in over half the tissues I have looked at there were areas of necrobiosis/ necrosis. Necrobiosis describes tissues which are devoid of cells with the extracellular matrix still intact. It is possible to visualise the larger ceramic particles associated with areas rich in macrophages or ghost like cell remnants in the necrobiotic tissue. 6. Are ceramics the ultimate in terms of inert debris or should we be looking at other types of material such as other plastics or carbon composites etc? I believe that the size of the particles is the most important determinant of osteolytic potential, provided that the material is not chemically reactive (ie bioinert). Carbon composites that we have tested in simple configuration wear tests also generate the majority of particles in the circa 10 nanometre sized range and have very low reactivity with macrophages. Langdown, A. J., R. J. Pickard, et al. (2007). "Incomplete seating of the liner with the Trident acetabular system: a cause for concern?" J Bone Joint Surg Br 89(3): Liang, B., K. Kawanabe, et al. (2007). "Polyethylene wear against alumina and zirconia heads in cemented total hip arthroplasty." J Arthroplasty 22(2): Nath, S., S. Bodhak, et al. (2007). "Tribological investigation of novel HDPE- HAp-Al2O3 hybrid biocomposites against steel under dry and simulated body fluid condition." J Biomed Mater Res A 83(1): Sedel, L. and A. Raould (2007). "Engineering aspect of alumina on alumina hip prosthesis." Proc Inst Mech Eng [H] 221(1): Sugano, N., T. Nishii, et al. (2007). "Mid-term results of cementless total hip replacement using a ceramic-on-ceramic bearing with and without computer navigation." J Bone Joint Surg Br 89(4): Tateiwa, T., I. C. Clarke, et al. (2007). "Surface micro-analyses of long-term worn retrieved "Osteal" alumina ceramic total hip replacement." J Biomed Mater Res B Appl Biomater 83(2): Walter, W. L., C. O'Toole G, et al. (2007). "Squeaking in ceramic-on-ceramic hips: the importance of acetabular component orientation." J Arthroplasty 22(4): Tribos Newsletter _TribosNL.indd 13 27/11/07 8:06:40 PM

14 YOUR TIME STARTS NOW... Dr Harlan C. Amstutz, MD Dr Amstutz is Professor Emeritus and former Chief of Orthopaedic Surgery at the University of California at Los Angeles. Dr. Amstutz is recognized worldwide as a preeminent orthopaedic surgeon and researcher in the field of joint replacement. He has authored countless articles, abstracts and book chapters; holds numerous patents for joint implant designs; and is highly sought as a lecturer to audiences worldwide. 1. I first worked as an orthopaedic surgeon at... The Hospital for Special Surgery in New York which is affiliated with Cornell Medical College, before a two-year stint in the military followed by an NIH fellowship in London. 2. I chose to do orthopaedics because... partly due to my interest in sports. I chose it after considerable thought in preference to general surgery. 3. The biggest impact on my orthopaedics career is... has been my training at The Hospital for Special Surgery, and then the subsequent collaborations with the high caliber surgeons when I was invited to join their practice there. 4. The thing I m most excited about for the future of orthopaedics in joint replacement is... the success we are having with resurfacing hips after working on that concept for 35 years. 5. My proudest achievement is the development of the modern day resurfacing hip. 6. The people who have influenced me most are that group at the Hospital for Special Surgery, in particular Dr Philip D Wilson Sr. and Dr Philip D Wilson Jr. as well as Dr. William Longmire who introduced me to surgery at UCLA. 7. When I was 7 years old I wanted to be a I can t remember, I don t think anyone ever asked. 8. I m always being asked when I m going to retire? 9. If I wasn t me I d like to be I wouldn t really want to be anyone else. 10. Friends say I am a workaholic, and they are probably right. 11. I wish I had I wouldn t change a thing, I d do it all over again. 12. I wish I hadn t... as above! 13. I wish I could be young again. 14. At the moment I m reading I m not reading anything at the moment as I have just finished writing a book on resurfacing with little time to spare. 15. The person I d most like to sit next to at a dinner party is my wife. 14 Tribos Newsletter _TribosNL.indd 14 27/11/07 8:08:46 PM