PREDICTION OF LONG-TERM POLYETHYLENE WEAR IN TOTAL HIP-ARTHROPLASTY, BASED ON EARLY WEAR MEASUREMENTS MADE USING DIGITAL IMAGE-ANALYSIS

The capability to reliably predict long-term in vivo wear of polyethyl ene would be of great value for the early identification of problemati c total hip designs. Formal quantitative estimates of long-term polyet hylene wear were made from a series of 197 patients who had a total hi p arthroplasty and who were followed for a minimum of 10 years; the es timates were based on the wear that was apparent radiographically at n ominally 2 years after the operation. A newly developed digital image- analysis edge-detection procedure was applied to 1,237 archived follow -up radiographs. The edge-detection measurements were analyzed with a robust regression random-coefficients statistical formulation develope d especially to address the distributions of wear rate observed across this population over time. Formal regression equations were reported, which can be used to estimate late-wear depth for a patient radiograp hed at a 2-year follow-up visit. Series wide, the correlation between predicted and observed wear depths was 0.73 at 4 years, with a correla tion decline of approximately 0.03 per additional year.