Implant holding power of the femoral head. A cadaver study of fracture screws.

The holding power against axial pull-out forces of eight different screws implanted in the femoral heads of cadavers was tested. The Olmed screw had the greatest resistance to pull-out forces followed by the recently designed Ullevaal screw with long threads, and the von Bahr screw. There were substantial differences in the holding power in the four sectors of the femoral head. The holding power was strongly correlated with the logarithm of the moment of inertia of the screw threads, which is a function of the area and number of the threads (r = 0.94, P = 0.0002).