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The Seven-Year Wear of Highly Cross-Linked Polyethylene in Total Hip Arthroplasty

A Double-Blind, Randomized Controlled Trial Using Radiostereometric Analysis

Thomas, Geraint E.R., MA, MRCS1; Simpson, David J., PhD1; Mehmood, Shahid, MRCS1; Taylor, Adrian, FRCS(Orth)1; McLardy-Smith, Peter, FRCS, MA1; Singh Gill, Harinderjit, DPhil1; Murray, David W., MA, MD, FRCS(Orth)1; Glyn-Jones, Siôn, MA, DPhil, FRCS(Orth)1

doi: 10.2106/JBJS.J.00287
Scientific Articles
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Background: The use of highly cross-linked polyethylene is now commonplace in total hip arthroplasty. Hip simulator studies and short-term in vivo measurements have suggested that the wear rate of highly cross-linked polyethylene is significantly less than that of conventional ultra-high molecular weight polyethylene. However, long-term data to support its use are limited. The aim of this study was to compare the intermediate-term steady-state wear of highly cross-linked polyethylene compared with that of conventional ultra-high molecular weight polyethylene acetabular liners in a prospective, double-blind, randomized controlled trial with use of radiostereometric analysis.

Methods: Fifty-four patients were randomized to receive hip replacements with either conventional ultra-high molecular weight polyethylene acetabular liners (Zimmer) or highly cross-linked polyethylene liners (Longevity; Zimmer). All patients received a cemented, collarless, polished, tapered femoral component (CPT; Zimmer) and an uncemented acetabular component (Trilogy; Zimmer). Clinical outcomes were assessed and the three-dimensional penetration of the head into the socket was determined for a minimum of seven years. Linear regression was used to calculate the steady-state wear rate following the creep-dominated penetration seen during the first year.

Results: At a minimum of seven years postoperatively, the mean total femoral head penetration was significantly lower in the highly cross-linked polyethylene group (0.33 mm; 95% confidence interval [CI], ±0.10 mm) than it was in the ultra-high molecular weight polyethylene group (0.55 mm; 95% CI, ±0.10 mm) (p = 0.005). The mean steady-state wear rate of highly cross-linked polyethylene was 0.005 mm/yr (95% CI, ±0.015 mm/yr), compared with 0.037 mm/yr (95% CI, ±0.019 mm/yr) for conventional ultra-high molecular weight polyethylene (p = 0.007). No patient in the highly cross-linked polyethylene group had a wear rate above the osteolysis threshold of 0.1 mm/yr, compared with 9% of patients in the ultra-high molecular weight polyethylene group.

Conclusions: This study demonstrates that highly cross-linked polyethylene has a significantly lower steady-state wear rate compared with that of conventional ultra-high molecular weight polyethylene. Longer-term follow-up is required to determine if this will translate into improved clinical performance and longevity of these implants.

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

1Biomedical Research Unit (G.E.R.T., D.J.S., S.M., H.S.G., D.W.M., S.G.-J.), Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences (NDORMS), and the Nuffield Orthopaedic Centre (A.T., P.McL.-S., D.W.M., S.G.-J.), Headington, Oxford OX3 7LD, United Kingdom. E-mail address for S. Glyn-Jones: sion.glyn-jones@ndorms.ox.ac.uk

Copyright © 2011 by The Journal of Bone and Joint Surgery, Incorporated
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