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

• Published in: Journal of bone and joint surgery. American volume 2011, Vol.93 (8), p.716-722
• Main Authors: Thomas, Geraint E.R., MA,MRCS, Simpson, David J., PhD, Mehmood, Shahid, MRCS, Singh Gill, Harinderjit, DPhil, Murray, David W., MA,MD,FRCS(Orth), Glyn-Jones, Siôn, MA,DPhil,FRCS(Orth), Taylor, Adrian, FRCS(Orth), McLardy-Smith, Peter, FRCS,MA
• Format: Article
• Language: English
• Subjects: Orthopedics
• ISSN: 0021-9355
• DOI: 10.1016/S0021-9355(11)70797-4

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