Biomechanical and range of motion analysis of two proximally fixed locking plate systems for fixation of proximal humeral fractures

Abstract

Background: Locking plate constructs have become the implant of choice for operative fixation of proximal humeral fractures. Plating systems that are fixed proximally (<1 cm from the tip of the greater tuberosity) have yet to be compared to systems affixed distally (>1 cm). This study evaluated range of motion and load to failure of two commonly used proximal humeral locking plate systems. Methods: Six pairs of cadaver shoulders were divided into two groups (R [proximally fixed] and L [distally fixed]). Range of motion was evaluated fluoroscopically before and after plate implantation. Fixation was removed to create a surgical neck fracture using an oscillating saw and then replaced. Load to failure was conducted using a mechanical testing system to evaluate differences in the strengths of the constructs. Results: Shoulder range of motion did not decrease significantly after plate placement within each group (L, P=0.23; R, P=0.99). Range of motion was not statistically different between the groups prior to plate fixation (P=0.88) or after (P=0.60). Average load to failure for groups L and R were 1635±374 N and 1613±269 N, respectively, and were not statistically different (P=0.91). Primary modes of failure for groups R and L were plate bending and failure of distal fixation, respectively. Conclusions: Mechanical strength of the locking plate constructs and range of motion after plate placement do not differ significantly between the proximally or distally placed proximal humeral locking-plate systems tested.