Weight bearing radiographs are not necessary for measurement of polyethylene penetration in total hip prostheses: A radiostereometric study of 111 patients examined in weight-bearing and supine position

Abstract

Background Controversy exists as to whether polyethylene (PE) penetration of hip prostheses is underestimated when the measurements are made on radiographs obtained in supine position as compared to weight-bearing position. Patients and methods We examined 111 patients by radiostereometric analysis (RSA) in the supine and weight-bearing positions. Results The mean 3-D penetration was 0.68 mm (SD 0.58, range 0.04–3.05) for the supine position and 0.70 mm (SD 0.57, range 0.08–3.01) for the weight-bearing position. The correlation between supine and weight-bearing examinations was 0.99 (p < 0.001). The degree of penetration made no difference. There was no statistically significant difference as to whether the first examination was performed early, i.e. after 3 months, or after 12 months (p = 0.7). Interpretation The small systematic difference in penetration values between the supine and the weight-bearing positions is of no clinical or methodological importance. ▪