Locking plates improve torsional resistance in the stabilization of three-part proximal humeral fractures

This study quantified the torsional resistance provided by locking plates and angled blade plates used to stabilize proximal humeral fractures. Three-part proximal humeral fractures were created in 6 pairs of cadaveric humeri. One specimen of each pair was reconstructed with a proximal humeral locking plate, whereas the other specimen was reconstructed with an angled blade plate. An external rotation torque, varying from 0 to 5 N-m, was applied to the humeral head until the head rotated 30° or 10,000 loading cycles were applied. The mean initial torsional stiffness was significantly larger for the locking plates (0.99 N-m/degree) than for the blade plates (0.59 N-m/degree). For each pair, the maximum rotation was larger for the blade plate than for the locking plate. For this in vitro model of a reconstructed 3-part proximal humeral fracture, the locking plate provided better torsional fatigue resistance and stiffness than the blade plate.