COMPARISON OF PREDICTED AND MEASURED CONTACT PRESSURES IN NORMAL AND DYSPLASTIC HIPS

Hip dysplasia, a congenital and developmental deformity characterized by malorientation and a reduction of contact area between the femur an d acetabulum, is the most common cause of osteoarthritis of the hip. A ccording to current estimates, dysplasia accounts for nearly 76% of al l cases of osteoarthritis, and many who are affected require a total h ip replacement before the age of 50. It is theorized that in the poorl y oriented and deformed pelvis, a reduction in contact area lends to a n increase in contact pressure during normal activities. Currently, cl inicians attempt to reposition the joint, assuming that improving the position of the existing contact surface will lead to decreased pressu res It is also assumed that improving certain geometric parameters cor relates indirectly with decreased contact pressures. Neither these sim ple estimates nor other non-invasive models have ever been shown to be related to contact pressure. The purpose of this study was to evaluat e a computerized method of predicting hip joint contact pressures, whi ch applies known hip joint reaction forces to the three-dimensional su rface of the hip joint. To this act, cadaveric and plastic pelvic mode ls were developed to test whether the computer model could predict the magnitude and location of maximum pressure. Mechanical testing reveal ed that the computer model could be used to predict pressure in cadave ric pelves at prescribed locations (r(2)=0.64). The computerized model could also be used to predict the magnitude and location of maximum p ressure in a series of plastic models where the lend vector and the de gree of dysplasia were parametrically varied (r(2)=0.7). These finding s suggest that the computer model may be useful in. identifying patien ts who will fail osteotomy or whether they can be used to select the b est osteotomy for each patient. (C) 1997 Elsevier Science Ltd for IPEM .