Unfavorable hip stress distribution after Legg–Calvé–Perthes syndrome: A 25‐year follow‐up of 135 hips

To study the effect of hip and pelvis geometry on development of the hip after Perthes disease, we determined the resultant hip force and contact hip stress distribution in a population of 135 adult hips of patients who had been treated for Perthes disease in childhood. Contra‐lateral hips with no record of disease were taken as the control population. Biomechanical parameters were determined by mathematical models for resultant hip force in one‐legged stance and for contact hip stress, which use as an input the geometrical parameters assessed from anteroposterior radiographs. The mathematical model for stress was upgraded to account for the deviation of the femoral head shape from spherical. No differences were found in resultant hip force and in peak contact hip stress between the hips that were in childhood subject to Perthes disease and the control population, but a considerable (148%) and significant (p < 0.001) difference was found in the contact hip stress gradient index, expressing an unfavorable, steep decrease of contact stress at the lateral acetabular rim. This finding indicates an increased risk of early coxarthritis in hips subject to Perthes disease. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:8–16, 2014.