[Biomechanical examination of stress distribution in the femoral neck for varus-implanted and valgus-implanted cups (author's transl)].

Femoral neck fractures occur after cup-prosthesis implantation and inadequate trauma. By reaming the head the tension stress in the lateral tension banding system of the femoral neck is reduced. Therefore high unphysiological bending moments occur in the medial trabecular system, which resists only high pressure forces. Our investigations showed that the unfavourable change in the stress distribution in the femoral neck is worse for the varus- than for the valgus-implanted cup. This could be the cause for the femoral neck fractures after cup implantation and inadequate trauma.