We investigated the static and cyclical strength of parallel and angulated locking plate screws using rigid polyurethane foam (0.32 g/cm(3)) and bovine cancellous bone blocks. Custom-made stainless steel plates with two conically threaded screw holes with different angulations (parallel, 10° and 20° divergent) and 5 mm self-tapping locking screws underwent pull-out and cyclical pull and bending tests.
The bovine cancellous blocks were only subjected to static pull-out testing.
We also performed finite element analysis for the static pull-out test of the parallel and 20° configurations.
In both the foam model and the bovine cancellous bone we found the significantly highest pull-out force for the parallel constructs.
In the finite element analysis there was a 47% more damage in the 20° divergent constructs than in the parallel configuration.
Under cyclical loading, the mean number of cycles to failure was significantly higher for the parallel group, followed by the 10° and 20° divergent configurations.
In our laboratory setting we clearly showed the biomechanical disadvantage of a diverging locking screw angle under static and cyclical loading.
2011-09-13
Eng.
The Journal of bone and joint surgery. British volume
University Hospital Münster, Department of Trauma Surgery, Waldeyerstrasse 1, Münster 48149, Germany. dirk.waehnert [at] aofoundation.org
J Bone Joint Surg Br. 2011 Sep;93(9):1259-64
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