Biomechanical Comparison of Dual and Posterior Locking Plates in an Ex Vivo Comminuted Olecranon Fracture Model

Abstract

Comminuted olecranon fractures are commonly fixed with posterior locking plates (PLPs). Though biomechanically validated, this method comes with risks of symptomatic implant prominence and wound breakdown. Dual locking plates (DLPs) placed on the medial and lateral surfaces of the olecranon theoretically avoid these risks and allow for fixation of proximal fracture fragments in multiple planes. A biomechanical comparison of DLP and PLP fixation would help to validate the use of DLPs in comminuted olecranon fractures. Seven matched pairs of cadaveric upper extremities were evaluated with quantitative computed tomography scans to evaluate bone mineral density (BMD). Osteotomies simulating comminuted olecranon fractures (Mayo Type IIB) were created and the specimens were fixed either with variable angle PLPs or variable angle DLPs. The specimens were then cyclically loaded and loaded to failure. The ultimate strength, fracture displacement, and mechanism of failure were recorded and compared across groups. The correlation between BMD and ultimate strength was analyzed. The mean total BMD was 0.79 g/cm2 (SD, 0.14 g/cm2). No specimen failed during cyclic testing. Five of 7 PLP specimens and 5 of 7 DLP specimens failed by fracture through the proximal screws though in different planes (sagittal vs axial splits, respectively). The mean ultimate strengths of the PLP (1077 N [SD, 462 N]) and DLP (1241 N [SD, 506 N]) groups were similar. There was a linear relationship between ultimate strength and BMD (R2= 0.33). Dual locking plates display biomechanical properties that suggest that they can be used in the fixation of comminuted olecranon fractures. Catastrophic failure of the fixation constructs occurs around stress risers at the proximal screws rather than due to displacement at the fracture itself. Dual locking plate constructs can be considered for use in the fixation of comminuted olecranon fractures.