A NOVEL MODEL TO PREDICT WEAR IN AN UNCEMENTED HIP REPLACEMENT WITH A CERAMIC ON POLYETHYLENE BEARING

Abstract

Introduction: An increasing number of young and active patients are undergoing total hip replacement (THR), placing greater demands on the longevity of the implant. One of the most common modes of failure of a THR is aseptic loosening secondary to wear. This study aims to evaluate wear rates seen in a ceramic on polyethylene bearing, and to produce a mathematical model that could be used to predict wear which would have a role in a day-to-day clinic environment.

Methods: Radiographs were examined from 59 uncemented total hip replacements performed between March 1993 and April 2004 comprising a ceramic head on a polyethylene liner. Wear measurements were made using a manual Livermore technique employing digital callipers (accuracy 0.01mm). Multiple radiographic parameters were analysed so that those affecting wear could be identified and included in a mathematical model to predict wear.

Results: 59 hips were measured in 43 patients. Average age at time of follow-up was 53 (34–76). The mean length of time between postoperative and follow-up x-rays was 53 months (11–162). Overall wear rates were 0.05mm/year and total wear increased with the length of time an implant had been in place. There was no correlation between femoral stem alignment or acetabular inclination and wear rates. Multivariate linear regression analysis revealed that sex and cup type were significant contributing variables to wear. A predictive model was produced with an R2 value of 0.543.

Conclusion: This study confirms low wear rates with a ceramic on polyethylene bearing. The mathematical model produced can predict the variability of wear in 54.3% of hips. Further refinement may enable the model to be used to identify risk factors and therefore patients that require greater scrutiny at follow-up.