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

Prasad Antapur, MRCS, FRCS (Tr&Orth)
Clinical Fellow in Arthroplasty,
University Health Network, Toronto Western Hospital
Toronto, ON

Rajiv Gandhi, M.D., FRCSC
Assistant Professor, Department of Surgery, University of Toronto,
University Health Network, Toronto Western Hospital,
Toronto, ON

Nizar Mahomed, M.D., ScD, FRCSC
Smith & Nephew Chair in Orthopaedic Surgery,
Associate Professor of Surgery, University of Toronto,
University Health Network, Toronto Western Hospital,
Toronto, ON

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-up1.

Bearing surface wear, leading to osteolysis and aseptic loosening, are the leading causes of late revision total hip arthroplasty, especially in younger, more active patients2-3.

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 (six-nine years follow up) are extremely encouraging with reported linear wear rates of 0.02 +/- 0.06mm/year4-5.

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 (28mm 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-poly 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 metal-on-poly hip replacements performed worldwide, there exists a case report in the literature describing local granuloma formation secondary to poly wear9. 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 ions6-7.

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.

The outcomes following revision surgery for failure secondary to ALVAL are poorer compared to revisions for other reasons8. Common finding in these patients is soft tissue necrosis which necessitates the use of constrained prostheses.

With increasing cost control measures now becoming common, the metal-on-cross-linked poly 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 the younger patient if a 19% reduction in revision rates can be demonstrated10. 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 metal-on-polyethylene has 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 metal-on-cross-linked polyethylene articulations, the above 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 metal-on-polyethylene hip replacement has a good predictable outcome and should outlast most of the patients for whom it is chosen.

Table: Hip Simulator Wear of Various Bearing Combinations*

Bearing Condition

Wear Rate (mm 3/million cycles)

Cobalt-chromium/polyethylene gamma sterilized in nitrogen


Cobalt-chromium/UHMWPE sequentially irradiated and annealed






*All wear measurements were made on hip joint simulator with crossing path motion. Loading pattern with maximal load or 2450 N and a minimum load of 150 N applied. Alpha fraction bovine calf serum was used as joint fluid.


Table showing the volumetric wear from metal-on-cross-linked poly is less than that of metal-on-metal articulation.

Reference: OKU - Hip and Knee Reconstruction 3; 2006, p 338


  1. Berry D.J., Harmsen W.S., Cabanela M.E., Morrey B.F. 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 Y.G., Kim S.Y., Park B.C., Kim P.T., Ihn J.C., Kim I.D. Uncemented Harris-Galante total hip arthroplasty in patients with osteonecrosis of the femoral head. A 10-16-year follow-up study. Acta Orthop
  3. Beaulé P.E., Campbell P., Mirra J., Hooper J.C., Schmalzried T.P. Osteolysis in a cementless, second generation metal-on-metal hip replacement. Clin Orthop Relat Res. 2001;386:159-65
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  5. Manning D.W., Chiang P.P., Martell J.M., Galante J.O., Harris W.H.; In vivo comparative wear study of traditional and highly cross-linked polyethylene in total hip arthroplasty; J Arthroplasty. 2005;20:880-6.
  6. Davies A.P., Willert H.G., Campbell P.A., Learmonth I.D., Case C.P.; An unusual lymphocytic perivascular infiltration in tissues around contemporary metal-on-metal joint replacements; J Bone Joint Surg Am. 2005;87:18-27
  7. Pandit H., Glyn-Jones S., McLardy-Smith P., Gundle R., Whitwell D., Gibbons C.L., Ostlere S., Athanasou N., Gill H.S., Murray D.W.; Pseudotumours associated with metal-on-metal hip resurfacings; J Bone Joint Surg Br. 2008;90:847-51
  8. Grammatopoulos G., Pandit H., Kwon Y.M., Gundle R., McLardy-Smith P., Beard, D.J., Murray D.W., Gill H.S. Hip resurfacings revised for inflammatory pseudotumour have a poor outcome. J Bone Joint Surg [Br] 2009;91-B:1019-24.
  9. eigh W., O'Grady P., Lawson E.M., Hung N.A., Theis J.C., 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.
  10. Bozic K.J., Morshed S., Silverstein M.D., Rubash H.E., and Kahn J.G. 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., Apr 2006; 88: 706 - 714.


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