MEASUREMENT OF POLYETHYLENE WEAR IN METAL-BACKED ACETABULAR CUPS .2. CLINICAL-APPLICATION

The new 3-dimensional technique was applied to the radiographs of 141 patients who had received Porous Coated Anatomic total hip prostheses, Values were obtained for the position of the acetabular cup, the 3-di mensional distance and direction of femoral head displacement, and the minimum volume of polyethylene debris produced. Mean age of the patie nts at the time of replacement was 61 years old; mean followup was 5.6 years (range, 4-7.2 years). Change in the position of the femoral hea d between initial and long-term followup films was assumed to represen t polyethylene wear, and formulas were used to calculate the minimal v olume of polyethylene debris produced, The overall rate of 3-dimension al femoral head displacement was 0.264 mm per year, almost twice that usually quoted in the current litera-ture for 2-dimensional linear wea r. A significant contribution to this value was made by anterior and p osterior displacement. Two-dimensional femoral head displacement (meas ured in the plane of anteroposterior radiographs) on the same patients was 0.149 mm per year. The mean minimum volume of polyethylene debris produced after 5.6 years was 0.448 cm(3) (range, 0.00-2.83 cm(3)), gi ving a mean rate of 0.079 cm(3) polyethylene debris produced each year . Thirteen patients in this series had radiologic osteolysis and a sig nificantly greater femoral head displacement and polyethylene volumetr ic wear than those with no osteolysis. Patients with a 32-mm femoral h ead diameter and a polyethylene liner <1 cm thick had a significantly greater amount of polyethylene wear. This series gives previously unav ailable data on 3-dimensional femoral head displacement and is the fir st report that correlates the minimum volume of polyethylene wear prod uced with radiologic osteolysis.