Bending burdening of stable and unstable per- and subtrochanteral fractures after osteosynthesis with Y-nails (Küntscher), Ender-nails, 130 degrees and 95 degrees angled plates of the AO were tested in a comparative experimental study. The unstable fractures were also tested after treatment with osteosynthesis and additional application of bone cement in the artificial defect. The essential results were as follows: in the group of stable pertrochanteral fractures the Ender-nails bear in the mean 147 kp, the 130 degrees angle plate 200 kp. In the fracture-group with lacking medial support a highly burdening osteosynthesis could only be achieved by filling up the defects with bone cement. The 95 degrees-angled plate-osteosynthesis combined with bone cement bearing more than 300 kp was superior to the other procedures in the unstable per- and subtrochanteral fractures. In our investigation the stabilizing forces of muscles and fascia have not been taken into consideration.