Biomechanics Research Today is a free monthly online journal that collates and summarizes the latest research about Biomechanics, including details on mechanics of living organisms, movement, locomotion, prosthetic limbs.

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.

von Schewelov T, Onsten I, Markusson P, Carlsson A

Department of Orthopedics, Lund University, Malmö University Hospital, SE-205 02 Malmö, Sweden. Thord.von_Schewelov@orto.mas.lu.se

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.

Published 14 March 2006 in Acta Orthop, 77(1): 104-8.
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