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In a comparative experimental study stability of different extra- and intramedullar methods of osteosynthesis for stable and unstable pertrochanteric fractures has been examined under dynamical stress. For the treatment of stable pertrochanteric fractures in old patients the intramedullar methods of osteosynthesis (nailing by Ender of Küntscher) were shown to be biomechanically superior. Extramedullar osteosyntheses (130 degrees and 95 degrees angled plate) also guaranteed very high stability; under permanent stress however angled plates showed metal fatigue. In case of unstable pertrochanteric fractures the osteosyntheses with additional application of bone cement produced sufficient stability under permanent stress. The importance of reconstructing a stable medial support for the biomechanics of osteosynthetic materials was emphasized. According to our results especially the combination of 95 degrees angle-plates with bone cement permits immediate mobilisation of old patients in case of unstable pertrochanteric fractures.

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.