The influence of femoral head shift on hip biomechanics: additional parameters accounted.

Pauwels' method of hip biomechanics can explain a negative influence of the lateral shift of the femoral head on the load of dislocated hip joint, but, the influence of the cranial shift of femoral head can not be explained. A calculation of hip balance which takes into consideration both lateral and cranial shifts of the femoral head is presented. Two pelvic radiographs were used; of an adult person and of a two year old child. One hip was normal, and other was dislocated. Force R was established using horizontal lever k(1), and a new vertical lever k(2). Graphically and mathematically the results show that the force R is always greater in the dislocated hip. Both lateral and cranial shifts contribute to this. The modification of Pauwels method described clearly demonstrates that not only lateral but also cranial shift of the femoral head in dislocated hip should be taken into consideration.