Rate of wear in total hip replacement.

The wear of high molecular weight polyethylene sockets was measured on radiographs, over a period of 9 to 10 years, in a group of patients whose ages averaged 73.3 years at the end of the period. The average rate of wear was 0.15 mm/year and 68 per cent of patients followed this pattern. Wear more than 2.5 mm in 10 years occurred in 15 per cent. There was a diminution in the rate of wear with the passage of time; in the second 5 years the rate of wear was approximately 40 per cent less than in the first 5 years. Body weight and physical activity did not appear to have any relationship to the final amount of wear. In a second series of very disabled subjects under 30 years of age (33 patients, 59 hips, followed only for an average of 38.4 months) the wear was rather more than in the previous series. Most remarkable was the performance of 4 patients, below the age of 50, who were considered completely normal for their age (category A); three of these wore less than the average for the main series.