Three-dimensional finite element analysis of Legg-Calve-Perthes disease.

We studied the theoretical stress distribution in the proximal femoral epiphysis by means of a three-dimensional finite element model that allowed simulation of the central epiphyseal necrosis found in Legg-Calve-Perthes disease. The model was altered to study effects of age, extent of necrosis, portion of gait cycle, and effects of osteotomy on containment. It was found that small infarcts were less likely to exhibit collapse because of stress shielding, which decreased when the infarct was extensive or the area was not contained. There was little difference in stresses regardless of age or portion of the gait cycle. Femoral and pelvic osteotomies did little to modify mechanical stresses, and specifically failed to stimulate stress shielding in the case of extensive necrosis. This study suggests that basic mechanical behavior of the femoral epiphysis is similar in younger and older children, and good results in the former may be due to remodelling and low body weight. Although containment may have a place in less extensive lesions, there is no obvious mechanical support for the practice of performing osteotomies in the face of extensive epiphyseal necrosis.