A sclerotic rim provides mechanical support for the femoral head in osteonecrosis.

Osteonecrotic collapse of the femoral head is a common refractory disease in orthopedics, and the occurrence of collapse is an important factor in the prognosis of this condition. Osteonecrotic collapse of the femoral head can be delayed or prevented by the formation of a sclerotic rim. This study used finite element analysis to evaluate the mechanical role of a proximal sclerotic rim on stress on the femoral head. The study used a healthy man who underwent computed tomography of both hips to generate 3-dimensional finite element models with different proportions of proximal rim sclerosis (0%, 30%, 50%, and 100%). Using a negative directional mechanical load of 400 N along the Z-axis, total deformation, deformation in the negative Z-axial direction (ie, direction of longitudinal compression), maximum principal stress, minimum principal stress, and contact pressure on necrotic tissue were evaluated. For 0%, 30%, 50%, and 100% rim sclerosis, total femoral head deformation was 0.21, 0.205, 0.20, and 0.19 mm, respectively, and maximum principal stress in compression was 9.83, 9.67, 9.16, and 9.05 MPa, respectively. Increases in proximal rim sclerosis decreased all of the measured outcomes. These results suggest that proximal rim sclerosis provides effective mechanical support for the femoral head, offers mechanical protection for necrotic tissue, decreases deformation of the femoral head, and delays or prevents collapse in osteonecrosis. Copyright 2015, SLACK Incorporated.