Biomechanical aspects of the development of aseptic necrosis of the femoral head.

With the advancement of computer technology it has been possible to determine stress distribution in bone by the finite-element method (FEM), for a pathomechanical analysis of aseptic necrosis of the femoral head. Development of aseptic necrosis of the femoral head has been considered to be coincident with ischemic changes in the bone. However, the area of necrosis in the femoral head does not correspond to vascular distribution. We speculated that not only biological, but also biomechanical factors might play an important role in the development of femoral head necrosis. A two-dimensional finite-element model, with 801 elements and 454 nodes, was constructed to mimic the hip joint. Conditions for the disease were simulated on the assumption that concentrated areas of high stress cause changes in the biomechanical properties of bone, according to Wolff's law, such as necrosis or sclerosis. Results of the simulation correlated well with clinical findings. Biomechanical factors should be considered, not only to prevent the collapse of bone structure but also to limit the spread of bone necrosis in the early phase of the disease.