Biomechanical comparisons of hook plate and screw fixations in split-type greater tuberosity fractures of the humerus.

Abstract

Screws and plate are commonly utilized for the fixation of split-type humeral greater tuberosity (GT) fractures. However, the mechanical properties of these 2 types of fixation methods have not been compared directly. The aim of the present study was to evaluate the classic 2 screws fixation with hook locking plate from a mechanical perspective. Sixteen synthetic humerii (Sawbones Pacific Research Laboratories, Vashon, WA, USA) were divided into 2 groups. An osteotomy was performed to simulate a split-type GT fracture. Group A (n=8) was fixed with 2 standard parallel screws. Group B (n=8) was fixed with a hook plate. Each specimen was tested with traction force at 45° shoulder abduction. Following the 20-N preload, a 500-cycle loading test was applied with a force ranging from 20 to 200N (valley/peak), and the interfragmental displacement was measured periodically at intervals of 100 cycles. Finally, all the specimens were pulled with destructive force at a rate of 5mm/min until catastrophic failure. The hook plate exhibited greater construct stiffness than the screw fixation (63.2±6.1N/mm vs. 40.9±3.4N/mm, P<.001). All of the specimens completed the entire cyclic loading test without catastrophic failure, and the fragment displacement after 500 cycles was 0.4±0.2mm for the hook plate and 2.1±0.3mm for screw fixation, which was statistically lower in the plate group (P<.001). In terms of failure load, the hook plate group exhibited a significantly greater value than the screw group (770.6±94.6 vs. 427.5±45.1N/mm, P<.001). The failure modes of both fixation methods were distinct. In humeral GT fracture fixation, hook plate fixation appears to offer greater construct stiffness and failure load while maintaining fragment stability to resist a physiological traction force. The current study provides support from a mechanical perspective for the clinical application of the hook plate.