A finite-element analysis of the effects of intertrochanteric osteotomy on stresses in femoral head osteonecrosis.

The efficacy of osteotomy for the precollapse stage of femoral head necrosis depends on altering load transmission. The alteration must reduce the stress levels on the infarcted bone during the process of repair. The prospects for success in this regard would likely be improved by the ability to predict reliably the stress changes derived from specific osteotomies for specific femoral head involvement patterns. For this reason, an anatomic three-dimensional finite-element model has been designed to compute necrotic femoral head stress changes that accompany varus, valgus, and rotational osteotomies. Four specific patterns of femoral head infarction are considered. Comparison of the patterns of load transmission at ten discrete instants (spanning the stance phase of the gait cycle) revealed that the critical stresses in the most commonly infarcted anterolateral and central femoral head regions occur just after the instant of heel-strike. For the femoral head with a deep, narrow lesion in the weight-bearing tract, and for classic wedge-shaped segmental infarct, the data showed that 30 degrees varus osteotomy was beneficial in reducing stress levels through much of the infarcted region. The 30 degrees valgus osteotomy was less successful. Neither 30 degrees anteversion nor 30 degrees retroversion osteotomies caused substantial changes in stresses for infarcted regions along the weight-bearing tract. For the case of a wide, shallow lesion or for whole femoral head involvement, none of the four osteotomies considered was able to achieve appreciable net reduction of stresses in weakened, infarcted regions.