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Journal of the American Academy of Orthopaedic Surgeons:
Perspectives on Modern Orthopaedics

Ceramic Materials as Bearing Surfaces for Total Hip Arthroplasty

D'Antonio, James A. MD; Sutton, Kate MA

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Perspectives on Modern Orthopaedics articles provide an objective appraisal of new or controversial techniques or areas of investigation in orthopaedic surgery.

Dr. D'Antonio is an active staff member at Sewickley Valley Hospital, Sewickley, PA. Ms. Sutton is Senior Manager, Academic Resources, Stryker Orthopaedics, Mahwah, NJ.

Dr. D'Antonio or a member of his immediate family has received research or institutional support, miscellaneous nonincome support, and royalties from Stryker, and is a consultant to or an employee of Stryker. Ms. Sutton is an employee of Stryker and holds stock or stock options in Stryker.

Reprint requests: Dr. D'Antonio, 1099 Ohio River Boulevard, Sewickly, PA 15143.

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Abstract

During the past decade, advances in total hip arthroplasty component design have produced implants with reliable clinical results in regard to fixation. The foremost unresolved challenge has been the development of bearing surfaces that can withstand the higher demands of younger and more active patients. New alternative bearings with superior wear characteristics that minimize debris include ceramic‐on‐ceramic, metal‐on‐metal, and highly cross‐linked polyethylenes in combination with ceramic or metal. Alumina‐on‐alumina ceramic bearings are extremely hard and scratch resistant and provide superior lubrication and wear resistance compared with other bearing surfaces in clinical use. Survivorship revision for any reason for the alumina ceramic bearings at 10 years was significantly higher compared with metal‐on‐polyethylene. Bearings currently being studied because of their encouraging wear performance in the laboratory are an alumina matrix (82% alumina, 17% zirconia, 0.3% chromium oxide), zirconium oxide, and ceramic‐on‐cobalt‐chromium.

Introduced in 1971 as commercially pure alumina, ceramic‐on‐ceramic bearings have been used for more than 35 years; the major advantages, compared with the risks, have been clearly identified. Important advances in the material properties of alumina were introduced in the 1990s through a hot isostatic pressing process, which greatly increased the durability of alumina ceramics (Biolox forte; CeramTec AG, Plochingen, Germany). The introduction in 2000 of an alumina matrix composite (Biolox delta; CeramTec AG) further improved the mechanical and wear performance of ceramic‐on‐ceramic bearings.1

The Autophor/Xenophor alumina prosthesis (Osteo AG, Selzach, Switzerland), introduced in Europe by Mittelmeier,2 began to be used in the United States in the late 1970s and early 1980s. Clinical results were less than satisfactory, with overall survivorship of between 75% to 84% after 10 years.3,4 Failures were related to both material and design, resulting in aseptic loosening and ceramic fracture, as well as an occasional report of significantly increased wear. The rate of ceramic fracture (3% to 5%) was predominantly due to material of large grain size, the presence of inclusions and grain boundaries, and poor tolerances for taper designs mating ceramic to the implants. Advances in ceramic materials have led to improved prosthetic design for implant fixation and the development of specific taper designs, as well as to a higher level of performance of ceramic bearings, providing excellent biocompatibility, improved mechanical strength, and superior wear characteristics.

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Alumina‐on‐alumina Ceramic Bearings

Currently available alumina ceramics are of high quality, with reduced grain size, inclusions, and grain boundaries. Alumina ceramics are extremely hard and scratch resistant, provide excellent biocompatibility, have superb chemical and hydrothermal stability as well as an extremely low coefficient of friction, are hydrophilic with superior lubrication, and offer superior wear resistance compared with other available bearing surfaces.5‐7 The material and wear properties of alumina ceramics support the use of larger‐diameter femoral heads now commonly used with other materials; with larger heads, there is typically no increase in wear, greater resistance to fracture, and limited potential for metal ion release. Gait and fluoroscopic analyses have demonstrated that femoral head separation from the acetabular liner is less for alumina‐on‐alumina bearings than for all other available couples; this is likely because of the increased wettability of the alumina.8 Current alumina Biolox forte bearings are proof‐tested before distribution and are mated with implant designs that have proven excellent fixation records, have high taper tolerances, and are designed to minimize the risk of ceramic impingement.9‐12

The major disadvantages of the alumina ceramic bearing include the risk of fracture; for some designs, chipping on insertion; and squeaking.9,12‐15 Early anecdotal reports suggest a fracture risk of 0.0083% (ie, 1 in 12,000 implants) for the ceramic acetabular insert and of 0.02% (1 in 5,000 implants) for the alumina ceramic head. In our own study group of 1,382 hips implanted before US Food and Drug Administration (FDA) approval in February 2003—a group in which postmarket surveillance is required—there has been one fracture of an acetabular insert (0.07%).9‐11 We estimate the risk of fracture over the lifetime of these implants is more likely to be in the range of 1 in 2,000 to 1 in 3,000 for femoral heads (ie, 0.05% to 0.03%) and 1 in 6,000 to 1 in 8,000 for the alumina ceramic acetabular insert (ie, 0.017% to 0.013%). Data collected by the manufacturer (CeramTec AG) on nearly 2 million distributed implants show the following: 50% of fractures occur within the first 12 months; 70% of fractures occur within 24 months; 83% of fractures occur within 36 months; fractures of alumina heads are more common than fractures of the acetabular insert; fractures of 28‐mm heads occur more frequently than do fractures of 32‐mm and/or 36‐mm heads; and zero‐degree heads have fewer fractures than do +5 or −5 head sizes.12

Ceramic chips that occur during prosthesis insertion are a risk with some designs. Our first prospective randomized study used a ceramic acetabular insert placed within a titanium shell; if the insert is not fully seated upon impaction, a peripheral chip can occur.9,11 We observed a peripheral chip in 1.2% of cases; however, none of these resulted in a fracture or in revision surgery. A subsequent design encased the ceramic acetabular component in a titanium sleeve, which eliminates the risk of insertional chips.10,11

Reported incidence of squeaking with alumina ceramic bearings ranges from 0.45% in a series of 2,716 ceramic implants13 to 7.0% in a series of 159 ceramic implants.14 Most reported series note that squeaking is rare and without clinical significance; however, on rare occasions, major squeaking has led to revision surgery.14,15 Edge loading with resultant stripe wear is the predominant cause; it results from microseparation.13,15‐17 Microseparation can occur from acetabular malpositioning, failure to reconstruct offsets and/or leg lengths, or from bony and/or soft‐tissue impingement. In the laboratory, squeaking can be produced by markedly roughening the articulating surfaces; completely creating a dry articulation; placing a 28‐mm head inside a 32‐mm socket; and repeatedly causing microseparation, which results in edge loading and stripe wear. Clinical reports have shown that edge loading has been found at the time of revision surgery on all retrievals in patients who previously reported squeaking.13,15,17 In one report, excessive acetabular anteversion out of the safe range was found for all patients with ceramic implants with and without squeaking who were matched for demographics. The authors reported a 2.7% incidence of squeaking, and five of six retrievals had signs of impingement.15

In a prospective randomized study comparing alumina ceramic bearings with conventional metal‐on‐polyethylene, a significant clinical advantage has been demonstrated.11 Survivorship revision for any reason for the ceramic bearings at 10 years was 97%, compared with 91.3% for the control metal‐on‐polyethylene bearings. Survivorship revision of cup inserts for the ceramic bearings was 98%, compared with 92% for the control metal‐on‐polyethylene bearings. The incidence of squeaking was <1%, with no patient dissatisfied, disabled, or requiring revision for noise.11

The superior wear and lubrication of alumina ceramic bearings make them an option for young, active patients. The advantages for each patient must be weighed against the risk of fracture of the ceramic component. For the surgeon, the operation is technically difficult for several reasons. There are fewer intraoperative prosthetic options, including only 0° acetabular liners and limited head lengths (−5 to +5 in 5‐mm increments). Also, acetabular positioning and combined acetabular and femoral anteversion, plus reconstruction of offsets and leg length, are crucial to minimize the risk of microseparation and impingement.

Ceramic fracture is a major complication, and early revision is imperative (Figure 1). A complete synovectomy to remove ceramic debris is necessary. The best options for revision, when possible, include ceramic‐on‐ceramic, followed by ceramic‐on‐highly crosslinked polyethylene, followed by metal‐on‐highly cross‐linked polyethylene. During revision surgery, a ceramic ball cannot be safely placed on a damaged trunnion. A second option is the revision Biolox head, which contains an inner metal sleeve; it is now available, is FDA approved, and is supplied by CeramTec AG. Ceramic‐on‐ceramic provides the best option because of its scratch resistance. The use of metal on a highly cross‐linked polyethylene is currently the most frequently used option, but long‐term results have yet to be determined. Reconstruction with metal‐on‐conventional polyethylene has been shown to carry a risk of accelerated wear and the need for early re‐revision.18,19

Figure 1
Figure 1
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Alumina Matrix Composite

The rationale for adding zirconia to alumina dates back more than 30 years. When zirconia particles are dispersed and encapsulated in the alumina matrix, expansion of their monoclinic crystals provides for volume expansion, which dissipates energy and impedes crack propagation. Extensive studies in the laboratory have demonstrated the hydrothermal stability of the alumina matrix, essentially eliminating the risk of surface phase transformation. This alumina matrix composite, Biolox delta, is 82% alumina, 17% zirconium oxide, 0.3% chromium oxide, and 0.6% strontium oxide.1 The addition of zirconium greatly increases the fracture toughness; the addition of chromium oxide recaptures the hardness of the basic alumina matrix. Wear studies with and without microseparation have produced wear rates three‐ to sixfold lower for Biolox delta compared with alumina‐onalumina Biolox forte. The mechanical properties of the alumina matrix composite, Biolox delta, compared with medical‐grade alumina are significantly improved: fracture toughness increased 150%, burst strength increased 160%, and four‐point bending strength improved 210%.1

The Biolox delta implant was introduced for widespread use in Europe in 2004 and has been approved for use as the ball heads articulating on polyethylene in the United States.1 Two premarket studies are underway investigating Biolox delta‐on‐Biolox delta as a wear couple for total hip replacement arthroplasty. To date, there has been no report of a fracture of a Biolox delta femoral head implant. Because of the Biolox delta's increased fracture toughness and burst strength, the expectation is that fracture would occur with far less frequency than the estimated fracture rate of alumina ceramic heads (0.02%).12 Compared with Biolox forte, Biolox delta femoral heads are offered in a wider range of head sizes in 2.5‐mm increments, which provides greater options for offset and leg length reconstruction at the time of total hip replacement arthroplasty.

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Ceramic‐on‐metal Articulation for Total Hip Arthroplasty

In a simulator study, Firkins et al20 demonstrated superior wear for alumina ceramic‐on‐metal articulations. Femoral heads 28 mm in diameter made of medical‐grade alumina (Biolox forte) were articulated against acetabular cups manufactured from medical‐grade, high‐carbon‐wrought cobalt‐chromium alloy. The implants were tested for 5 million cycles. Wear and surface analyses were performed every 1 million cycles.

The results were compared with metal‐on‐metal articulations that used medical‐grade, low‐carbon, cobaltchromium alloy femoral heads against medical‐grade, high‐carbon, cobaltchromium alloy sockets. The metal‐on‐metal bearings initially showed high bedding‐in and subsequently developed a steady‐state volumetric wear rate of 1.23 mm3 per 1 million cycles. No bedding‐in period was observed with the ceramic‐on‐metal, and a volumetric wear rate of 0.01 mm3 per 1 million cycles was reported. This represents more than a 100‐fold decrease in wear with the ceramic‐on‐metal articulation. Surface analysis of the ceramic head showed no signs of wear or change in surface roughness. Metal particles from both articulations were of nanometer size (6 to 30 nm). In addition, the ceramic‐on‐metal articulations produced slightly smaller particles, although they were far fewer in number.20 Clinical studies are currently under way to assess the performance of these bearings.

The potential advantage of this novel ceramic‐on‐metal bearing is lower wear and the generation of significantly fewer metal particles compared with currently available metal‐on‐metal bearing surfaces. This bearing combination allows for the use of large femoral heads, similar to metal‐on‐metal bearings. With larger ceramic heads, the fracture risk is reduced, and an increased number of femoral head options are available to the surgeon. Potential disadvantages of this new bearing articulation include the risk of a ceramic femoral head fracture and its as‐yet unknown clinical performance.

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Ceramic‐on‐polyethylene Bearings

Alumina and zirconia ceramic femoral heads have long been used to articulate against polyethylene because of their resistance to scratching. Zirconia femoral heads have not performed as well as alumina because of phase transformation that can occur over a 10‐year period, leading to accelerated wear. A further reason for the performance of zirconia femoral heads was an isolated manufacturing‐related fracture problem created with zirconia heads sintered in a tunnel furnace introduced in 1998.21‐23 Clinical studies on the wear of implanted alumina femoral heads on conventional polyethylene compared with metal‐on‐polyethylene have shown mixed results.24‐28 Simulator studies have demonstrated a 50% lower wear for alumina ceramic femoral heads against highly cross‐linked polyethylene for both 28‐ and 36‐mm heads compared with metal‐on‐polyethylene.24‐27 Because of its advantages (ie, scratch resistance, lubrication, burst strength), the Biolox delta alumina matrix composite may offer a promising alternative bearing against highly cross‐linked polyethylene.1

The major advantages of ceramicon‐polyethylene bearings include hardness, scratch resistance, a lower coefficient of friction compared with other available bearings, increased wettability for improved lubrication, and superior wear resistance. In the presence of third‐body wear, their scratch resistance offers a further advantage over cobalt‐chromium heads. The disadvantage to ceramicon‐polyethylene bearings primarily involves the risk of ceramic fracture and the resultant difficult revision procedure. There is some evidence that metal transfer to the ceramic can occur with metal contact on reduction of the total hip; such transfer can increase surface roughness, possibly leading to increased polyethylene wear.28

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Oxidized Zirconium Bearing Surface

A zirconium oxide surface (Oxinium; Smith & Nephew, Memphis, TN) is produced by a thermally driven oxygen diffusion that transforms the metallic zirconium alloy surface into a durable, low‐friction oxide. This oxidized layer is not a ceramic coating but rather is a transformation of the surface that is 5 to 10 μm thick. The oxidized layer is much harder and more scratch resistant than the untreated alloy, although it is less hard and less scratch resistant than a true alumina ceramic surface. This bearing surface preparation has been available for the hip since October 2002 and available on the femoral component of total knees for more than 8 years. To date, no in vivo experience with Oxinium for total hip arthroplasty has been reported in the literature. Laboratory studies have shown that the surface is durable, will not fracture, and is chemically bonded to the zirconium substrate.29‐31

According to wear simulator study results, the major advantage of Oxinium technology is lower wear of both smooth and roughened Oxinium femoral heads against conventional polyethylene and cross‐linked polyethylene, compared with cobaltchromium‐on‐polyethylene.29‐31 Additionally, the Oxinium surface is more scratch resistant than that of cobalt‐chromium femoral heads. Also, the surgeon has the same options with regard to femoral head sizes and offsets as those available with cobalt‐chromium femoral heads.

The major disadvantages of the Oxinium surface preparation are that it is a new technology with no short‐ or long‐term known clinical benefit; to date, there have been no published clinical results. The durability of this surface has been shown to be quite high in vitro; however, if the surface did fail in vivo for any reason, the zirconium substrate would be an inferior bearing surface. Retrievals of Oxinium femoral heads have been reported to show heavy damage in patients who had recurrent dislocations31,32 (Figure 2). Both the femoral head and the acetabular liner after clinical instability should be replaced during revision surgery.

Figure 2
Figure 2
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Discussion and Summary

Alumina ceramic bearings are an attractive option for the young, active patient because of the material's superior wear, improved lubrication, and resultant low volume of less reactive particulate debris. The disadvantages include the remote risk of fracture, the small risk of squeaking, and fewer head and liner options available. Alumina ceramic‐on‐polyethylene offers lower wear than do metal‐on‐polyethylene articulations. Alumina‐on‐highly cross‐linked polyethylene has greater resistance to wear, particularly in the presence of third‐body particles. The recently introduced alumina matrix (Biolox delta) offers increased burst strength, greater fracture toughness, and more options at the time of surgery for head offset replacement. Zirconium oxide (Oxinium) femoral heads have been shown in the laboratory to be hard and scratch resistant; also, they yield low wear in the simulator. However, clinical studies are necessary to determine whether the wear of Oxinium is equivalent to the extremely low wear that has been demonstrated with current alternative bearings (ie, cobalt chromium‐onhighly cross‐linked polyethylene, ceramic‐on‐ceramic, and metal‐on‐metal articulations). The novel “hard‐on‐softer” ceramic‐on‐metalbearing has extremely low wear in the laboratory compared with other bearing surfaces, including hard‐onhard bearings. Prospective studies are currently under way to determine the risks and benefits of this new concept.

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References

Evidence‐based Medicine: Level I/II prospective, randomized studies include references 9‐11 and 25. Level III/IV case reports and case‐control studies include references 2‐4, 6, 12‐18, 21‐24, 26‐29, 31, and 32. The remaining references are expert opinion, gait analyses, and laboratory studies.

Citation numbers printed in bold type indicate references published within the past 5 years.

1. Kuntz M: Validation of a new high performance alumina matrix composite for use in total joint replacement. Semin Arthroplasty 2006;17:141-145.

2. Mittelmeier H: Abstract: Eight years of clinical experience with self-locking ceramic hip prosthesis, “Autophor.” J Bone Joint Surg Br 1984;66:300.

3. Nizard RS, Sedel L, Christel P, Meunier A, Soudry M, Witvoet J: Ten year survivorship of cement into ceramic total hip prosthesis. Clin Orthop Relat Res 1992;282:53-63.

4. Sedel L, Kerboull L, Christel P, Meunier A, Witvoet J: Alumina-on-alumina hip replacement. Results of survivorship in young patients. J Bone Joint Surg Br 1990;72:658-663.

5. Clarke IC: Role of ceramic implants: Design and clinical success with total hip prosthetic ceramic-to-ceramic bearings. Clin Orthop Relat Res 1992;282:19-30.

6. Clarke I, Willmann G: Structural ceramics in orthopaedics, in Cameron HU (ed): Bone Implant Interface. St. Louis, MO: Mosby, 1994, pp 203-252.

7. Germain MA, Hatton A, Williams S, et al: Comparison of the cytotoxicity of clinically relevant cobalt chrome and alumina wear particles in vitro. Biomaterials 2003;24:469-479.

8. Dennis DA, Komistek RD, Mahfouz MR: Kinematic evaluation of total hip arthroplasty with various bearing materials. Presented at Bioceramics and Alternative Bearings in Total Joint Arthroplasty: 11th Biolox Symposium, Rome, Italy, June 30—July 1, 2006.

9. D'Antonio J, Capello W, Manley M, Naughton M, Sutton K: Alumina ceramic bearings for total hip arthroplasty: Five-year results of a prospective randomized study. Clin Orthop Relat Res 2005;436:164-171.

10. D'Antonio JA, Capello WN, Manley MT, Naughton M, Sutton K: A titaniumencased alumina ceramic bearing for total hip arthroplasty: 3 to 5 year results. Clin Orthop Relat Res 2005;441:151-158.

11. D'Antonio JA, Capello WN, Bierbaum B, Manley M, Naughton M: Ceramicon-ceramic bearings for total hip arthroplasty: 5-9 year follow-up. Semin Arthroplasty 2006;17:146-152.

12. Garino J, Rhaman MN, Bal BS: Reliability of modern alumina bearings in total hip replacements. Semin Arthroplasty 2006;17:113-119.

13. Walter WL, O'toole GC, Walter WK, Ellis A, Zicat BA: Squeaking in ceramicon-ceramic hips: The importance of acetabular component orientation. J Arthroplasty 2007;22:496-503.

14. Jarrett CA, Ranawat A, Bruzzone M, Rodriguez J, Ranawat C: Abstract: The squeaking hip: An under-reported phenomenon of ceramic-on-ceramic total hip arthroplasty. Final Program of the 16th Annual Meeting of the American Association of Hip and Knee Surgeons. Rosemont, IL: American Association of Hip and Knee Surgeons, 2006, p 20.

15. Restrepo C, Parvizi J, Purtill J, Sharkey P, Hozack W, Rothman R: Abstract: Noisy ceramic hip: Is component malposition the problem? Final Program of the 16th Annual Meeting of the American Association of Hip and Knee Surgeons. Rosemont, IL: American Association of Hip and Knee Surgeons, 2006, p 21.

16. Walter WL, Lusty PJ, Watson A, et al: Stripe wear and squeaking in ceramic total hip bearings. Semin Arthroplasty 2006;17:190-195.

17. Walter WL, Insley GM, Walter WK, Tuke MA: Edge loading in third generation alumina ceramic-on-ceramic bearings: Stripe wear. J Arthroplasty 2004;19:402-413.

18. Allain J, Roudot-Thoraval F, Delecrin J, Anract P, Migaud H, Goutallier D: Revision total hip arthroplasty performed after fracture of a ceramic femoral head. A multicenter survivorship study. J Bone Joint Surg Am 2003;85: 825-830.

19. Barrack RL, Burak C, Skinner HB: Concerns about ceramics in THA. Clin Orthop Relat Res 2004;429:73-79.

20. Firkins PJ, Tipper JL, Ingham E, Stone MH, Farrar R, Fisher J: A novel low wearing differential hardness, ceramic-on-metal hip joint prosthesis. J Biomech 2001;34:1291-1298.

21. Masonis JL, Bourne RB, Ries MD, McCalden RW, Salehi A, Kelman DC: Zirconia femoral head fractures: A clinical and retrieval analysis. J Arthroplasty 2004;19:898-905.

22. Minakawa H, Stone MH, Wroblewski BM, Lancaster JG, Ingham E, Fisher J: Quantification of third-body damage and its effect on UHMWPE wear with different types of femoral heads. J Bone Joint Surg Br 1998;80:894-899.

23. Santos EM, Vohra S, Catledge SA, McClenny MD, Lemons J, Moore KD: Examination of surface and material properties of explanted zirconia femoral heads. J Arthroplasty 2004;19(7 suppl 2):30-34.

24. Urban JA, Garvin KL, Boese CK, et al: Ceramic-on-polyethylene bearing surfaces for total hip arthroplasty: 17-21 year results. J Bone Joint Surg Am 2001; 83:1688-1694.

25. Wroblewski BM, Siney PD, Dowson D, et al: Prospective clinical and joint simulator studies of a THA using alumina ceramic heads and a crosslinked polyethylene cup. J Bone Joint Surg Br 1996;78:280-285.

26. Zichner LP, Willert HG: Comparison of alumina-polyethylene and metalpolyethylene in clinical trials. Clin Orthop Relat Res 1992;282:86-94.

27. Clarke IC, Gustafson A: Clinical and hip simulator comparisons of ceramic-on-polyethylene and metal-on-polyethylene wear. Clin Orthop Relat Res 2000;379: 34-40.

28. Della Valle AG, Doty S, Gradl G, Labissiere A, Nestor BJ: Wear of a highly crosslinked polyethylene liner associated with metallic deposition on a ceramic femoral head. J Arthroplasty 2004;19: 532-536.

29. Bourne RB, Barrack R, Rorabeck CH, Salehi A, Good V: Arthroplasty options for the young patient: Oxinium on crosslinked polyethylene. Clin Orthop Relat Res 2005;441:159-167.

30. Ries MD, Salehi A, Widding K, Hunter G: Polyethylene wear performance of oxidized zirconium and cobaltchromium knee components under abrasive conditions. J Bone Joint Surg Am 2002;84(suppl 2):129-135.

31. Jaffe WL, Strauss E, Kummer FJ: Abstract: Types of THA head damage due to dislocation and reduction: Causes and effects. Final Program: 74th Annual Meeting Proceedings of the American Association of Orthopaedic Surgeons. Rosemont, IL: American Academy of Orthopaedic Surgeons, 2007, p 418.

32. Kop AM, Whitewood C, Johnston D: Damage of oxinium femoral heads subsequent to hip arthroplasty dislocation: Three retrieval case studies. J Arthroplasty 2007;22:775-779.

© 2009 American Academy of Orthopaedic Surgeons

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