[Effects of hollow shaft endoprosthesis on stress distribution in cortical bone].

Generally, conduction of the forces from the distal end of the prosthesis stem into the surrounding cortical bone effects a local load increase in the bone. Where bone and stem are in close contact "stress protection" is hardly avoidable, and this, together with the load increase, results in the formation of a "plug of bone" beneath the tip of the prosthesis. Since the prosthesis stem rests on this bone "plug", additional "stress protection" of the femur results, which may possibly lead to total failure of the femur and/or the prosthesis. A 3-dimensional FEM-analysis shows that the hollow-stem prosthesis helps to decrease the stress peak beneath the tip of the prosthesis, while at the same time the stress in the proximal cortical bone increases. The increase in the loading of the bone inevitably causes a reduction in bone breakdown through "stress shielding" in this region.