Preservation of the natural femoral head in the presence of osteonecrosis depends upon avoiding collapse of structurally compromised necrotic cancellous bone. The stressto-strength ratio (SSR) of epiphyseal bone indexes its mechanical response to the presence of necrotic bone and to joint-preserving treatments such as coring and cortical bonegrafting. Previous finite element modeling demonstrated that the location, diameter, and degree of tract penetration during these operative treatments can produce load-transfer alterations which achieve lower, presumably beneficial, stresses within the femoral head.

Methods to construct three-dimensional finite-element models with actual surgical graft placement directly from the sparse data of clinical radiographs and magnetic resonance images of patients undergoing vascularized fibular grafting for osteonecrosis of the femoral head were developed. The mechanical efficacy of each treatment was indexed by the SSR in femoral head host cancellous bone. This new generation of patient-specific finite element models, which demonstrated marked differences in femoral head load transfer between untreated lesions, surgically realized graft placement, and alternative treatment modalities, adapts to clinically available data.