[Fractures of the femural shaft following trepanation of the corticalis and how to avoid it. At the same time an article on changing hip endoprothesis (author's transl)].

The problem of trepanation of the corticalis is investigated in 2 cases of femoral shaft fractures following a lateral trepanation of the femur, which can very often not be avoided in performing a necessary change of the hip prothesis. It can be demonstrated that because of the stress on the femur and its mechanical characteristics (material distribution, density distribution, breaking strength, "structure" strength and the histological structure), a lateral trepanation of the femoral corticalis is weakening the bone in its mechanically most stressed part whereas an anterior fenestration is mechanically much better. Considering the distribution of the strain in differently formed notches with rapid increase of strain with local rigidity in a pointed notch a mechanically much better rounding of the notch is suggested.