Evaluation of ischial weight-bearing orthoses, based on in-vivo hip joint force measurements.

The reduction of hip joint forces by ischial weight-bearing orthoses, used for the treatment of Legg-Perthes and other joint diseases, was measured in vivo in a patient with two instrumented endoprostheses. Three different types of orthoses reduced hip joint loading by about 30%, independent of their cuff design and the position in which the femur was held. The direction of the joint forces was changed in such a way that the size of the load-carrying joint areas decreased by up to 3.4% with two conventional orthoses. With the third model with improved containment of the femoral head this area increased by up to 8.2%. All the orthoses studied support the pelvis too close to the affected joint, leading to insufficient load reduction. A design concept is proposed which prevents tilting of the pelvis in the frontal plane and may improve the force reduction at the hip joint.