Slipped capital femoral epiphysis: factors affecting shear forces on the epiphyseal plate.

Very little is known regarding the magnitude of physiological shear forces in the normal capital femoral epiphyseal plate. Changes in these forces related to deformities in the proximal femur have been postulated to increase significantly the shear forces and predispose to slipped epiphysis. By force analysis techniques, a three-dimensional model has been developed to study the change in shear forces that might be expected from abnormal angulation in the frontal and sagittal planes. This study suggests that within the range of normal activity, shear forces on the epiphyseal plate are well below the critical values required to cause a slip. Angular deformities of up to 30 degrees in either the frontal or sagittal planes, by themselves, are unlikely to raise these forces to a critical value.