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All Hip Replacement Patients Should Receive Metal-on-Polyethylene Bearings

Scroll down to respond to the OrthopaedicsOne Poll: Highly cross-linked polyethylene bearings should be the implant of choice for young and active hip replacement patients

Our colleagues from the Université de Montréal and the University of Toronto present an important and quite à propos debate on the clinical usage and indications of hard-on-hard bearings versus the routine use of highly cross-linked polyethylene.

As it occurs commonly in orthopaedics, we tend to push new designs as the solution to all of our previous difficulties and challenges. For bearing surfaces, this is especially the case when we consider issues such as osteolysis, dislocation, and minimizing the morbidity of revision hip surgery.A perfect example is the monoblock acetabular components with a metal-on-metal bearing,1 which were initially designed for hip resurfacing, but that are now used for primary total hip replacement to minimize the risk of dislocation. Recent ion data2 and clinical data, however, are showing higher ion levels and a higher incidence of adverse tissue reactions3 with this construct, compared with a modular acetabular shell with a metal-on-metal bearing and 28- and 36-mm femoral head, which conversely have been shown to be a reliable construct at mid-term follow-up.4,5 The same can be said with highly cross-linked polyethylene, in which wear rates with 28- and 32-mm heads have shown excellent results.6,7 But to also address the problem of instability, 36- and 40-mm heads are commonly used in young active patients, and early in vivo data are showing higher wear rates.8

Consequently, we need to curb our initial enthusiasm to avoid introducing unforeseen problems. In that same line, the new buzzword with metal-on-metal bearings is "pseudotumour";9 however, it should be pointed out that pseudotumours are not a new phenomenon in total hip arthroplasty, since they were first associated with metal-on-polyethylene bearings in the mid-1980s.10,11 More importantly, although the focus of research and industry has been on prosthetic longevity, lack of revision surgery does not necessarily equate to long-term improvement on overall quality of life after total hip replacement.12

We hope you enjoy this debate!


  1. Beaule PE, Mussett SA, Medley JB. Metal-on-metal bearings in total hip arthroplasty. Instr Course Lect 2010;59:17-25.
  2. Garbuz DS, Tanzer M, Greidanus NV, Masri BA, Duncan CP. Metal-on-metal hip resurfacing versus large-diameter head metal-on-metal total hip arthroplasty: a randomized clinical trial. Clin Orthop Relat Res 2009;Epub.
  3. Langton DJ, Jameson SS, Joyce TJ, Hallab NJ, Nargol AFV. 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 2010;92B:38-46.
  4. Migaud H, Jobin A, Chantelot C, Giraud F, Laffargue P, Duquennoy A. Cementless metal-on-metal hip arthroplasty in patients less than 50 years of age: comparison with a matched control group using ceramic-on-polyethylene after a minimum 5-year follow-up. J Arthroplasty Suppl.3 2004;19:23-28.
  5. Engh CA, Jr, MacDonald SJ, Sritulanondha S, Thompson A, Naudie D, Engh CA. 2008 John Charnley award: metal ion levels after metal-on-metal total hip arthroplasty: a randomized trial. Clin Orthop Relat Res. 2009;467:101-11.
  6. Digas G, Karrholm J, Thanner J, Malchau H, Herberts P. Highly cross-linked polyethylene in total hip arthroplasty: randomized evaluation of penetration rate in cemented and uncemented sockets using radiostereometric analysis. Clin.Orthop.Rel.Res. 2004;429:6-16.
  7. McCalden RW, MacDonald SJ, Rorabeck CH, Bourne RB, Chess DG, Charron KD. Wear rate of highly cross-linked polyethylene in total hip arthroplasty. A randomized controlled trial. J Bone Joint Surg 2009;91A:773-82.
  8. Lachiewicz PF, Heckman DS, Soileau ES, Mangla J, Martell JM. Femoral head size and wear of highly cross-linked polyethylene at 5 to 8 years. Clin Orthop Relat Res 2009;467:3290-3296.
  9. Glyn-Jones S, Pandit HP, Kwon YM, Doll H, Gill HS, Murray DW. Risk factors for inflammatory pseudotumour formation following hip resurfacing. J Bone Joint Surg 2009;91B:1566-74.
  10. Griffiths HJ, Burke J, Bonfiglio TA. Granulamotous pseudotumors in total joint replacement. Skeletal.Radiol. 1987;16:146-52.
  11. Svensson O, Mathiesen EB, Reinholt FP, Blomgren G. Formation of a fulminant soft-tissue pseudotumor after uncemented arthroplasty. A case report. J Bone Joint Surg 1988;70A:1238-42.
  12. Gartland JJ. Orthopaedic clinical research: deficiencies in experimental design and determination of outcome. J Bone Joint Surg. 1988;70A:1357-64.
  13. Franzen H, Johnsson R, Nilsson LT. Impaired quality of life 10 to 20 years after primary hip arthroplasty. J Arthroplasty 1997;12:21-24.

Reprinted with permission from the Summer 2010 issue of COA Bulletin

Scroll down for additional points of view and to see what others have to say

Viewpoint 1: Prasad Antapur, MRCS, FRCS (Tr&Orth); Rajiv Gandhi, MD, FRCSC; Nizar Mahomed, MD, ScD, FRCSC

The Case for MOP Bearings for All THA Patients

Over the past few years, alternative bearing surfaces have been introduced to increase the longevity of the implant and reduce the risk of osteolysis secondary to wear debris. Improvements have resulted in an increased choice of implants for patients and their surgeons. Current demographic trends indicate that younger patients are now undergoing total hip replacements while aiming to return to an active lifestyle postoperatively.

This debate is focused on the advantages and disadvantages of using metal heads on polyethylene acetabuli.

Metal-on-conventional ultra high molecular weight polyethylene in total hip arthroplasty has produced very good long-term results, with reports of implant survivorship of almost 80% at over 20 years follow-up.1 Bearing surface wear, leading to osteolysis and aseptic loosening, are the leading causes of late revision total hip arthroplasty, especially in younger, more active patients.2,3


Recently, cross-linked ultra high molecular weight polyethylene has been introduced. Initial in vitro studies showed marked improvement in wear characteristics, with up to 95% reduction in volumetric wear. Current reports looking at mid-term results (6-9 years follow up) are extremely encouraging, with reported linear wear rates of 0.02 +/- 0.06mm/year.4,5 No osteolytic lesions in the acetabulum or femur have been described. The decreased wear rates with the use of cross-linked polyethylene may reduce the need for revision arthroplasty by reducing the development of osteolysis and late dislocations. The use of highly cross-linked polyethylene liners offers the surgeon a wide choice of implants with regard to head sizes (28 mm to 40 mm), elevated liners (0-10 – 20 Deg), and offset options (standard or lateralized). The risk of dislocation can be further reduced by the use of a large head with an elevated lip liner.

Enough experience has been gained following a well-performed metal-on-polyethylene (MOP) total hip replacement to recommend its widespread use. The signs of impending failure are well recognized and timely intervention results in a good outcome.

Out of the hundreds of thousands of MOP hip replacements performed worldwide, only one case report in the literature describes local granuloma formation secondary to poly wear.6 However, unlike metal-on-metal articulations, no systemic toxicity has been described. Recent reports about metal hypersensitivity and subsequent tissue necrosis secondary to ALVAL (aseptic lymphocytic vasculitis and associated lesions) have been described. This is thought to be due to a delayed type IV hypersensitivity reaction to the metal ions.7,8 Outcomes following revision surgery for failure secondary to ALVAL are poorer compared to revisions for other reasons.9 A common finding in these patients is soft tissue necrosis, which necessitates the use of constrained prostheses.

In addition, elevated serum metal ion levels are a constant finding in patients with a metal-on-metal bearing. The long-term consequences of this are not known. Patients with chronic diseases such as chronic renal failure have a poor capacity to excrete cobalt and chromium ions. Increased metal ion levels locally, especially chromium, have been shown to induce chromosomal aberrations. Long-term monitoring studies with serial metal ion levels are in progress.

With increasing cost control measures now becoming common, the MOP bearing is significantly more cost-effective when compared to newer alternate bearing articulations. Current literature justifies the increased cost of newer and more expensive bearing surfaces in younger patients if a 19% reduction in revision rates can be demonstrated.10 Long-term results of the newer metal-on-metal articulations are awaited.

In young patients, it may be acceptable to explore alternative bearing surfaces, but widespread adoption seems unnecessary as MOP bearings have a proven track record without catastrophic complications. The benefits of alternate bearing surfaces in reducing the rates of revision arthroplasty have not yet been conclusively demonstrated. This is even more important in light of promising clinical and laboratory reports of reduced wear and osteolysis with newer, highly cross-linked ultra high molecular weight polyethylene bearings.

Reported survivorship for conventional polyethylene varies between 90% at 15 years to over 80% at 20 years. Given the extremely low wear rates with MOP articulations, these survivorship results may be extrapolated to indicate a survivorship in excess of 90% at 25 years.

All bearings will wear, but by avoiding distant toxicity and high cost, the MOP hip replacement has a good predictable outcome and should outlast most of the patients for whom it is chosen.

Reprinted with permission from the Summer 2010 issue of COA Bulletin


  1. Berry DJ, Harmsen WS, Cabanela ME, Morrey BF. Twenty-five-year survivorship of two thousand consecutive primary Charnley total hip replacements: factors affecting survivorship of acetabular and femoral components. J Bone Joint Surg Am 2002;84:171-7
  2. Kim YG, Kim SY, Park BC, Kim PT, Ihn JC, Kim ID. Uncemented Harris-Galante total hip arthroplasty in patients with osteonecrosis of the femoral head. A 10-16-year follow-up study. Acta Orthop 2005 Feb;76(1):42-8
  3. Beaulé PE, Campbell P, Mirra J, Hooper JC, Schmalzried TP. Osteolysis in a cementless, second generation metal-on-metal hip replacement. Clin Orthop Relat Res. 2001;386:159-65
  4. McCalden RW, MacDonald SJ, Rorabeck CH, Bourne RB, Chess DG, Charron KD. Wear rate of highly cross-linked polyethylene in total hip arthroplasty; a randomized controlled trial. J Bone Joint Surg Am 2009;91:773-782
  5. Manning DW, Chiang PP, Martell JM, Galante JO, Harris WH. In vivo comparative wear study of traditional and highly cross-linked polyethylene in total hip arthroplasty. J Arthroplasty 2005;20:880-6.
  6. Leigh W, O'Grady P, Lawson EM, Hung NA, Theis JC, Matheson J. Pelvic pseudotumor: an unusual presentation of an extra-articular granuloma in a well-fixed total hip arthroplasty. J Arthroplasty 2008;23:934-38
  7. Davies AP, Willert HG, Campbell PA, Learmonth ID, Case CP. An unusual lymphocytic perivascular infiltration in tissues around contemporary metal-on-metal joint replacements. J Bone Joint Surg Am 2005;87:18-27
  8. Pandit H, Glyn-Jones S, McLardy-Smith P, et al. Pseudotumours associated with metal-on-metal hip resurfacings. J Bone Joint Surg Br 2008;90:847-51
  9. Grammatopoulos G, Pandit H, Kwon YM, et al.Hip resurfacings revised for inflammatory pseudotumour have a poor outcome. J Bone Joint Surg Br 2009;91-B:1019-24
  10. Bozic KJ, Morshed S, Silverstein MD, Rubash HE, Kahn JG. Use of cost-effectiveness analysis to evaluate new technologies in orthopaedics. The case of alternative bearing surfaces in total hip arthroplasty. J. Bone Joint Surg Am 2006; 88:706-14

Viewpoint 2: Sanket Diwanji, MS (Ortho); Pascal-André Vendittoli MD, MSc, FRCSC

The Case Against MOP Bearings for All THA Patients

In the 1960s, Sir John Charnley pioneered the use of metal-on-polyethylene (MOP) bearing surfaces for total hip arthroplasty (THA), which have been improving the quality of life (QOL) in patients with arthritis ever since. When their application was extended to young and active patients, MOP bearings had earlier and higher rates of failure.

Osteolysis associated with bearing wear was identified as a culprit in early failures.1 The incidence of osteolysis in most series beyond 10 years and in a few series of less than 10 years exceeds that of sepsis, dislocation, fatal pulmonary embolization, nerve damage, and other complications.2 Periprosthetic fractures are also attributed, in part, to femoral osteolysis.3-5 Apart from causing osteolysis, polyethylene wear per se decreases range of motion (ROM) due to femoral head penetration into the polyethylene. Polyethylene wear also causes increased rates of late dislocation and heightened torsional forces on the implant-bone interface resulting in mechanical loosening.6

Newer bearing options have been introduced to tackle the problem of wear in hip arthroplasty. Highly cross-linked polyethylene (HCPE) has reduced the wear rate in laboratory and clinical studies with follow-up of up to 5 years. However, clinical follow-up of less than 5 years has little value, as the evolution of radiographic evidence is a slow process in periprosthetic osteolysis.2 Even though absolute wear is decreased with HCPE, the particles generated are biologically active and have the potential of inducing osteolysis.7


Investigation of HCPE performance in the presence of third-body wear or rough counter surface (femoral head’s surface roughness of more than 0.9 µm) has established that cross-linking does not provide any advantage and wear is greater than with conventional polyethylene.8 Recently published data indicate excessive volumetric wear with 36- to 40-mm heads and HCPE liners.9 These authors urge caution with larger femoral heads in young and active patients and in those with low risk of dislocation. Cross-linking alters the material properties of polyethylene, which has evoked concerns about loss of fracture toughness and the brittle nature of HCPE. Baker and colleagues have demonstrated that true stress at breakpoint and resistance to crack propagation are inversely related to cross-linking radiation dose; these are attributed to decreased plasticity at the fracture tip.10

The science of tribology has shown that hard-on-hard bearings — metal-on-metal (MOM) and ceramic-on-ceramic (COC) components — with small clearance, good surface finish and optimal implant sphericity minimize wear.11-13 COC bearings demonstrated excellent resistance to surface damage, such as scratching, by their high-level hardness and offer the lowest wear rate of all available bearings. In MOM bearings, after an initial run-in period, the wear rate declines to below 1 µm/million cycles.14 They are also known to self-polish with usage, a phenomenon unique to these bearings. Thus, in terms of wear, these hard-on-hard bearings present a clear potential for wear reduction and longer survivorship when compared with MOP.

In the early years, osteolytic lesions were reported after MOM implants with low-on-high carbon content, which are now recognized as detrimental factors.15,16 On the other hand, some implants made of high-on-high carbon content CrCo (for example, 28-mm Metasul, Zimmer, USA) have consistently presented a low wear rate, low serum ion levels,17,18 and good to excellent mid-term clinical results with rare osteolytic lesions.17,19-21

Recent problems encountered with MOM (early failures, metal allergy, and pseudotumour) have raised concerns in the orthopaedic community. We must differentiate bearing-related problems from fixation and implant positioning issues. Many large-diameter MOM bearings have been introduced recently with new implant designs, such as thin monoblock acetabular component,22-24 new acetabular porous coatings,23 new neck sleeves for leg length adjustment, and various modular femoral head designs.25,26 Early failures in of these many cases are attributable to rapid introduction of untested implants on the market. Biological response such as pseudotumour and metal allergic reaction seems to occur in abnormally high wear situations, either due to poor implant positioning or design.

In our experience, only three cases of pseudotumour out of 3,400 hips were found (AAOS 2010: A survey on the incidence of pseudotumours with MOM hip resurfacing in Canadian academic centres). We are not aware of any published pseudotumour cases with Metasul 28 mm, which has been in use for more than 20 years. Thus, not all MOM bearings perform similarly.

We believe that MOM implants are a good option for THA in young and active patients. MOM bearing acetabular components can be modular or monoblock. Modular inserts can be used with good track record acetabular components and allow insertion of screws to supplement primary fixation. Very good clinical results (low ions, absence of osteolysis, no pseudotumour and favourable revision rate) have been reported with the original Metasul 28 mm since its introduction in 1989.27,28

More recently, monoblock acetabular components have been introduced. These thin components allow anatomical bearing diameter for hip resurfacing or large-diameter head THA. Large-diameter heads eliminate joint stability problems and permit unrestricted postoperative ROM with a return to demanding sports activities or occupations, such as plumbing, policing, and roofing, a major benefit for patient QOL. Also, patients with very small acetabulums (less than 48 mm) can receive hard-on-hard bearings and large-diameter heads with MOM bearings. Otherwise, cemented polyethylene bearings with 22- or 28-mm metal head would have to be used. However, as mentioned earlier, some of these large diameter head THA implants presented early failures that can be attributed to introduction of deficient designs (new porous coating, corrosion at the neck sleeve, etc) and not related to the MOM bearing itself.23-26

COC bearings have shown significantly lower wear rates than MOP in a randomized trial.29 But as with MOM implants, the European experience with these bearings was largely disregarded, and this led to multiple failures due to design modifications. Recent problems with new alumina implants in metal-back inserts30,31 or polyethylene sandwich32,33 have been clearly documented. These design problems should not diminish the performance of well-functioning COC bearing implants. For the moment, COC bearings do not allow for monoblock acetabular implants and thus limit head diameter to 32 or 36 mm in sockets exceeding 48-52 mm in most instances.

Each bearing surface has its limitations:

  • MOP, wear
  • MOM, elevated metal ions and hypersensitivity
  • COC, bearing fracture and squeaking

However, all bearings do not perform alike, with good and bad performers being found in each group. Bearing selection for THA should be based on individual patient requirements rather than one-size-fits-all. MOP bearings may not be the best option for patients with a very small acetabulum (less than 50 mm), young patients with high physical demands, good candidates for hip resurfacing, and subjects with increased postoperative dislocation risk. COC bearings could be an attractive alternative when MOM bearings are contraindicated (ie, patients with known metal allergies, women of child-bearing age, and patients with chronic renal failure). MOP should be limited to older patients or those with low physical activity. We strongly believe that not all total hip replacement patients should receive MOP bearings.

Reprinted with permission from the Summer 2010 issue of COA Bulletin


  1. Willert HG, Bertram H, Buchhorn GH. Osteolysis in alloarthroplasty of the hip. The role of ultra-high molecular weight polyethylene wear particles. Clin Orthop Relat Res 1990;(258):95-107.
  2. Harris WH. Wear and periprosthetic osteolysis: the problem. Clin Orthop Relat Res 2001;(393):66-70.
  3. Charnley J, Halley DK. Rate of wear in total hip replacement. Clin Orthop Relat Res 1975;(112):170-9.
  4. Clarke IC. Wear in total hip replacement. Hip arthroplasty, ed. A. HC. 1991, New York: Churchill Livingstone 535-554.
  5. Yamaguchi M, Bauer TW, Hashimoto Y. Deformation of the acetabular polyethylene liner and the backside gap. J Arthroplasty 1999;14(4):464-9.
  6. Wroblewski BM. Wear and loosening of the socket in the Charnley low-friction arthroplasty. Orthop Clin North Am 1988;19(3):627-30.
  7. Ingram JH, Stone M, Ingham E. Effect of crosslinking on biological activity of UHMWPE wear debris. Trans Orthop Res Soc 2003; 28:1439.
  8. McKellop H, DiMaio W, Lancaster JG. Wear of gammacrosslinked polyethylene acetabular cups against  roughened femoral balls. Clin Orthop Relat Res 1999;(369):73-82.
  9. Lachiewicz PF, H.D., Soileau ES et a, Femoral head size and wear of highly cross linked polyethylene at 5 to 8 years. Clin Orthop Relat Res 2009;467(12):3290-6.
  10. Baker DA, Bellare A, Pruitt L. The effects of degree of crosslinking on the fatigue crack initiation and propagation resistance of orthopedic-grade polyethylene. J Biomed Mater Res A 2003;66(1):146-54.
  11. Dowson D, et al. A hip joint simulator study of the performance of metal-on-metal joints: Part II: design. J Arthroplasty 2004;19(8 Suppl 3):124-30.
  12. Dowson D, et al. A hip joint simulator study of the performance of metal-on-metal joints: Part I: the role of materials. J Arthroplasty 2004;19(8 Suppl 3):118-23.
  13. Rieker CB, et al. Influence of the clearance on in-vitro tribology of large diameter metal-on-metal articulations pertaining to resurfacing hip implants. Orthop Clin North Am 2005;36(2):135-42, vii.
  14. McMinn DJ, Daniel J, Ziaee H. Controversial topics in orthopaedics: metal-on-metal. Ann R Coll Surg Engl 2005;87(6):411-5.
  15. Park YS, et al. Early osteolysis following second-generation metal-on-metal hip replacement. J Bone Joint Surg Am 2005;87(7):1515-21.
  16. Milosev I, Pisot V, Campbell P. Serum levels of cobalt and chromium in patients with Sikomet metal-metal total hip replacements. J Orthop Res 2005;23(3):526-35.
  17. Brodner W. et al. Serum cobalt levels after metal-on-metal total hip arthroplasty. J Bone Joint Surg Am 2003;85-A(11):2168-73.
  18. Vendittoli PA, et al. Randomised controlled trial comparing two methods of acetabular cup positioning during total hip arthroplasty. Hip Int 2007;17(3):137-42.
  19. Sieber HP, Rieker CB, Kottig P. Analysis of 118 second-generation metal-on-metal retrieved hip implants. J Bone Joint Surg Br 1999;81(1):46-50.
  20. Delaunay C. Can metal-on-metal bearings improve the longevity of total hip prostheses?. Rev Chir Orthop Reparatrice Appar Mot 2005;91(1):70-8.
  21. Najjar D, et al. Mechanisms of damage to metal-on-polyethylene articulating surfaces of total hip prostheses: influence of intra-articulate migration of metallic debris. Rev Chir Orthop Reparatrice Appar Mot 2004;90(8):732-40.
  22. Berton C, et al. The Durom large diameter head acetabular component: early results with a large-diameter metal-on-metal bearing. J Bone Joint Surg Br;92(2):202-8.
  23. Long, W.T., et al., Failure of the Durom Metasul acetabular component. Clin Orthop Relat Res 2010;468(2):400-5.
  24. Langton DJ, et al. 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 2010;92(1):38-46.
  25. Garbuz DS, et al. The John Charnley Award: Metal-on-metal hip resurfacing versus large-diameter head metal-on-metal total hip arthroplasty: a randomized clinical trial. Clin Orthop Relat Res 2010;468(2):318-25.
  26. Vendittoli P-A, Amzica T, Roy A, et al. Metal ion release with large-diameter metal-on-metal hip arthroplasty. J Arthroplasty 2011;26(2):282-8.
  27. Delaunay C. [Can metal-on-metal bearings improve the longevity of total hip prostheses?] Rev Chir Orthop Reparatrice Appar Mot 2005;91(1):70
  28. Migaud H, Jobin A, Chantelot C, Giraud F, Laffargue P, Duquennoy A. Cementless metal-on-metal hip arthroplasty in patients less than 50 years of age: comparison with a matched control group using ceramic-on-polyethylene after a minimum 5-year follow-up. J Arthroplasty 2004;19(8 Suppl 3):23
  29. Vendittoli PA, Girrard J., Lavigne M, et al. Comparison of alumina-alumina to metal-polyethylene bearing surfaces in THA : A randomized study with 4- to 9- years follow-up. Acta Orthop Belg 2007;73:468-477.
  30. Miller AN, et al. Incidence of ceramic liner malseating in Trident acetabular shell. Clin Orthop Relat Res 2009;467(6):1552-6.
  31. Langdown AJ, Pickard RJ, Hobbs CM, et al. Incomplete seating of the liner with the Trident acetabular system: a cause for concern? J Bone Joint Surg 2007;89(3):291-5.
  32. Milosev I, et al. Dissociation of the metal inlay from the polyethylene liner in an uncemented threaded cup. Arch Orthop Trauma Surg 2005;125(2):134-41.
  33. Kircher J, et al. Extremely high fracture rate of a modular acetabular component with a sandwich polyethylene ceramic insertion for THA: a preliminary report. Arch Orthop Trauma Surg 2009;129(9):1145-50.


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