Biomechanical properties of bone and cartilage in growing femoral head following ischemic osteonecrosis

Legg-Calve-Perthes disease (LCPD) is one of the most common causes of a permanent deformity of the femoral head among pediatric hip disorders. Mechanical loading of the osteonecrotic femoral head undergoing repair is thought play a significant role in the development of the femoral head deformity. This study measured the mechanical properties in uniaxial unconfined compression tests of epiphyseal bone and cartilage from immature femoral heads following surgical induction of osteonecrosis using an established piglet model. Both the modulus and yield strength of bone cores from the infarcted heads were significantly lower by 50%-60% than those of the contralateral normal control heads by 2 weeks after surgery and they remained this low for 8 weeks. No consistent difference in the bone mineral or collagen content per dry weight in the bone cores was observed. Cartilage modulus and yield strength were significantly lower at 2 weeks and remained low for 8 weeks. Cartilage collagen and glycosaminoglycan content per dry weight did not differ significantly between control and infarcted heads at any time point. However, the relative proportion of chondroitin 6-sulfate increased significantly over the 8-week postoperative period, which correlated with an increase in cartilage thickness. These results indicate that the deterioration of the mechanical properties of the epiphyseal bone and cartilage likely plays a significant role in the pathogenesis of the femoral head deformity in LCPD.