WEAR PERFORMANCE OF HIGHLY CROSSLINKED POLYETHYLENE IN TOTAL HIP ARTHROPLASTY: A PROSPECTIVE RANDOMISED CONTROLLED STUDY AT 5 YEARS MINIMUM FOLLOW-UP

Abstract

This study reports on the clinical and wear performance of a prospective randomised controlled trial comparing highly cross-linked (XLPE) to conventional polyethylene (PE) in total hip arthroplasty at five years minimum follow-up.

One hundred patients enrolled in a prospective randomised controlled trial received identical hybrid total hip arthroplasties with the exception of the polyethylene insert. Fifty patients received a PE liner (2.5 MRads; gamma-in-nitrogen sterilization) and fifty patients received a XLPE liner (10Mrads; gas-plasma sterilization). Clinical outcomes were determined using Harris Hip, WOMAC and SF-12 scores by an independent study nurse. Femoral head penetration rates were determined using a validated radiographic technique (Hip Analysis Suite 8.0.1.1) based on radiographs at six weeks, one year and yearly post-operatively. Linear regression analysis was performed for both the entire polyethylene groups and on each patient, where the slope represents the steady state head penetration rate (after bedding in) from one to five years follow-up.

None of the patients were lost to follow-up, however, nine patients were deceased before their five year follow-up. Two patients have been revised for loose stems. At average follow-up of 6.0 years (range 5.1–6.8 years), there were no differences in Harris Hip, WOMAC or SF-12 scores. XLPE had a significantly lower (p= 0.03) steady-state head penetration rate of 0.018 mm/year compared to 0.050 mm/year for XLPE (approximately 64% reduction). Analysis of individual patient’s head penetration rates demonstrated a similar significantly lower rate with XLPE (0.004 ± 0.067 mm/year) compared to PE (0.045 ± 0.083 mm/year). Interestingly, when examined by gender, the male PE group had a significantly higher head penetration rate (0.081 ± 0.084 mm/year) than both the male and female XLPE (−0.013 ± 0.104, 0.011 ± 0.074 mm/year, respectively).

At minimum five years follow-up, there were no clinical differences between groups. After bedding-in, there was a significant lower head penetration rate with XLPE compared to PE. Thus, mid-term follow-up appears to demonstrate a significant wear reduction (based on head penetration rates) afforded by first generation XLPE. Long-term follow-up is required to demonstrate the clinical benefit of this new material.