The formation and function of the sclerosis rim in the femoral head: A biomechanical point of view.

Sclerosis rim surrounding the necrotic area is commonly found in necrotic femoral head, but the biomechanical function of sclerosis rim has received relatively little attention. Little is known about the formation and natural history of sclerosis rim. In the present work, we assume that the necrotic change may trigger bone remodeling process in the femoral head, which took place according to Huiskes' bone remodeling model incorporated with the FE simulations as described earlier. We then investigate the function of sclerosis rim as a mechanical supporter in delaying further collapse of the femoral head based on our sclerotic rim model. The main tasks of this study are: (1) simulation of the density distribution in the necrotic femoral head after bone remodeling; (2) calculation of maximal von Mises stress in the subchondral bone of the weight-bearing area of the femoral head over the necrotic area before and after bone remodeling. Results show that the sclerotic rim is, from the biomechanical point of view, an adaptive response to the decrease in elastic modulus of the femoral head, and that the sclerotic rim that acts as a compensatory structural reinforcement can usually significantly reduce the maximal stress in the subchondral bone when the lesion is small, but not when the lesion is large.