It has been demonstrated that in the normal hip abduction to adduction motion of the femoral head in the neutral position is equivalent to internal to external rotation of the femoral head in the 90 degree flexed position. For similiar reasons external to internal rotation of the femoral head in the neutral position is equivalent to abduction to adduction motion in the 90 degree flexed position. Due to the architecture of the hip joint, therefore, the hip motion in some pathological conditions can be anticipated and explained.
