Abstract
Introduction: Posterior dislocation of replacement hips may occur during extreme hip flexion and adduction. Hip braces restrict movement, but they are uncomfortable and have a low patient compliance. Knee braces are more comfortable, and also restrict hip movement, by tightening the hamstrings. This study investigated the effect of a knee brace on hip movement.
Methods: A magnetic tracker was used to measure the movement of 20 normal hips in 20 volunteers, aged 25–62. Sensors were attached over the iliac spine and lateral thigh. Subjects were asked to lie on a couch and flex and adduct their hip three times with their knee bent and three times with their knee braced in extension. During each movement the tracker recorded hip flexion and adduction angles, with an accuracy of 0.15 degrees.
Results: With the knee flexed, the mean hip flexion angle was 66.00 (SD 11.0). With the knee braced, the mean hip flexion angle was 35.30 (SD 15.4). Hence the knee brace reduced hip flexion by 46 % (30.70) (paired t-test, P < < 0.001).
With the knee flexed, the mean hip adduction angle was 23.70 (SD 7.1). With the knee braced, the mean hip adduction angle was 21.60 (SD 5.6). Hence the knee brace reduced hip adduction by 9 % (2.10). This was not significant (paired t-test, P = 0.3).
Discussion: These results indicate that a knee brace can restrict hip flexion by almost 50%. This information may be useful for patients in whom restriction of hip flexion provides hip stability. As the knee brace is more comfortable than the hip brace, a better patient compliance is expected.
Correspondence should be addressed to BHS c/o BOA, at the Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London, WC2A 3PE, England.
