[Experimental studies of the optimal plate pre-bending angle in compression osteosynthesis with reference to the plastic-elastic behavior of the osteosynthesis plate]

In order to achieve uniform pressure distribution in the osteotomy crack, the plate used in plate osteosynthesis has to be over-bent prior to fixation. To determine experimentally the extent to which the plate is usually pre-bent "intuitively", the bone axis was measured with narrow autocompression plates pre-bent at various angles on bones of cadavers, using a laser-optic system. The optimal pre-bending angle for the six-hole plate was found to be 3-5 degrees, for the eight-hole plate 5-6.5 degrees. The importance of the sliding-hole screw with regard to stability is pointed out. Both elastic and plastic deformation are affected when the plate bends back. However, the strength of the osteosynthesis is only affected by the plastic portion. An examination of the plate after osteosynthesis revealed the 20-30% of the original pre-bending had been lost; this corresponds approximately to the plastic portion.