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Wear Rate of Highly Cross-Linked Polyethylene in Total Hip Arthroplasty

A Randomized Controlled Trial

¹ Division of Orthopaedic Surgery, London Health Sciences Centre, University Campus, 339 Windermere Road, London, ON N6A 5A5, Canada. E-mail address for R.W. McCalden: richard.mccalden{at}lhsc.on.ca
² The Hand and Upper Limb Centre, St. Joseph's Health Centre, 268 Grosvenor Street, Suite D2-167, London, ON N6A 4L6, Canada

Investigation performed at University Hospital, University of Western Ontario, London, Ontario, Canada

Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from Zimmer, Inc., Warsaw, Indiana. In addition, one or more of the authors or a member of his or her immediate family received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from a commercial entity (Zimmer, Inc.). Also, a commercial entity (Zimmer, Inc.) paid or directed in any one year, or agreed to pay or direct, benefits in excess of $10,000 to a research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which one or more of the authors, or a member of his or her immediate family, is affiliated or associated.

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Methods: One hundred patients were enrolled in a prospective, randomized controlled study comparing highly cross-linked and conventional polyethylene acetabular liners in total hip arthroplasty. Fifty patients were in each group. At the time of follow-up, clinical outcomes were assessed and steady-state femoral head penetration rates (after bedding-in) for each patient were calculated with use of a validated radiographic technique. In addition, a statistical comparison of polyethylene wear between groups was performed with use of generalized estimating equations.

Results: At a mean of 6.8 years postoperatively, there were no differences between the two polyethylene groups with regard to the Harris hip score, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), or Short Form-12 (SF-12) score. The mean femoral head penetration rate in the first through fifth years was found to be significantly lower in the group treated with the highly cross-linked polyethylene (0.003 mm/yr [95% confidence interval, ±0.027]) than it was in the group treated with conventional polyethylene (0.051 mm/yr [95% confidence interval, ±0.022]) (p = 0.006). Men treated with a conventional polyethylene liner had a significantly higher (p 0.012) femoral head penetration rate (0.081 mm/yr [95% confidence interval, ±0.065]) than both men and women with a highly cross-linked liner (–0.013 mm/yr [95% confidence interval, ±0.074] and 0.009 mm/yr [95% confidence interval, ±0.028], respectively). The general estimating equations demonstrated that the group with a highly cross-linked polyethylene liner had a significantly lower femoral head penetration rate than the group with a conventional polyethylene liner (p = 0.025), and a significantly higher femoral head penetration rate was demonstrated in men with a conventional polyethylene liner when compared with both men and women with a highly cross-linked liner (p = 0.003).

Conclusions: At a minimum of five years postoperatively, the steady-state femoral head penetration rate associated with this first-generation highly cross-linked polyethylene liner was significantly lower than that associated with a conventional polyethylene liner. Long-term follow-up is required to demonstrate the clinical benefit of this new material.

Level of Evidence: Therapeutic Level I. See Instructions to Authors for a complete description of levels of evidence.

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