Mechanical behavior of the femoral head in Legg-Perthes disease.

The research described herein is concerned with the development of a "restricted" three-dimensional finite element model of the femoral head that permits the mechanical behavior of the hip joint in Legg-Perthes' disease to be simulated and studied. This "restricted" finite element model allows the femoral head to be treated as a non-axisymmetrically loaded axisymmetric solid of revolution. In order to minimize computer costs, and in recognition of the several uncertainties present in the mechanical description of the system, a number of simplifying assumptions are introduced. These assumptions include an axisymmetric geometry, axisymmetric and linear-elastic material properties, small deformation and displacement, and an approximate load distribution on the femoral head. The computer analyses reveal the relation between the magnitude and the distribution of the stresses in the femoral head and such parameters as (1) the position in the gait cycle, (2) the thickness of the articular cartilage, (3) the extent of the necrotic bone, and (4) the type of corrective osteotomy. A sampling of the preliminary results is presented and some conclusions are drawn with respect to the implications of the study.