Load transmission through the proximal femur of the growing child: a finite element analysis

Growth-related variations in the distribution of mechanical stress in the normal juvenile proximal femur are explored using a computer-based finite element stress analysis technique. Input data for the model are obtained from serial patient roentgenograms and from laboratory compression tests of fresh autopsy material. The results for the limiting case of epiphyseal closure (18-year-old male) are in substantive agreement with previous experimental and mathematical studies of the adult proximal femur. The computational results for the juvenile hip show that in spite of the complex morphological alterations occurring during growth, the basic mechanisms of load transmission at first ambulation are still operational at skeletal maturity. Foremost among these are the distally-concentrated weight bearing compressive stresses in the primary trabeculation system, the abductor-induced tensile stresses in the greater trochanter, and the large longitudinal stresses within the proximal femoral cortices. As growth advances, however, the importance of transverse compressive stresses in the proximal lateral metaphysis progressively diminishes, while shearing stresses in the plane of the epiphyseal plate increase markedly. These two major growth-related changes results largely from decreases in the neck-shaft angle, and if excessive, may be implicated in development coxa vara or slipped capital femoral epiphysis.