EARLY WEAR PERFORMANCE OF HIGHLY CROSS-LINKED POLYETHYLENE IN TOTAL HIP ARTHROPLASTY: A PROSPECTIVE RANDOMISED CONTROLLED STUDY

Abstract

Introduction and Aims: While highly cross-linked polyethylene has achieved widespread clinical use based on laboratory testing showing significant wear reduction, there is little clinical information demonstrating its benefits in vivo. This study reports the early clinical and wear performance of a prospective randomised controlled trial comparing highly cross-linked to standard polyethylene.

Method: One hundred patients were enrolled in a prospective randomised controlled trial in which all patients received a hybrid THR (cemented Versys stem, Triology cementless acetabulum). The two groups were virtually identical in terms of age, weight, male/female ratio and received identical hip implants, except that one half (50 patients) randomly received a highly cross-linked polyethylene liner. Clinical outcomes were determined using Harris hip, WOMAC and SF-12 scores. Two-dimensional (2D) and three-dimensional (3D) wear rates were determined using a validated radiographic technique based on AP and lateral radiographs at six weeks and one, two and three years post-operatively.

Results: At two years minimum follow-up (range two to four years), there were no differences in Harris hip, WOMAC or SF-12 scores. No patients were lost to follow-up, although five patients had died of unrelated causes. There were no infections, dislocations or revisions to date. Wear analysis at one-year post-op showed high penetration rates for both groups (mean 3D wear approximately 0.25 mm/year) consistent with the bedding-in phenomena. At most recent radiographic follow-up (two or three years), there was a statistically significant although modest difference in wear rates between the two groups with a 2D and 3D wear rate of 0.14±0.10 mm/yr and 0.15±0.02 mm/yr respectively for conventional polyethylene compared to 0.09±0.04 mm/yr and 0.11±0.02 mm/yr for cross-linked polyethylene. This represented a 32 and 29 percent reduction in 2D and 3D wear rates respectively with cross-linked polyethylene.

Conclusion: At early follow-up, there were no clinical differences. There was a modest wear reduction (approximately 30%) with highly cross-linked polyethylene, considerably less than expected based on laboratory testing. Longer follow-up, after the bedding-in process is completed, is required to demonstrate the wear reduction afforded by highly cross-linked polyethylene.