Repair of transverse midbody proximal sesamoid bone fractures (PSB) are difficult to treat and the use of conventional implants is often associated with fracture gap displacement and inadequate repair. There is a need to identify more effective implants for repair of midbody PSB fractures. We hypothesized that the 3.5mm BSF would have reduced gap formation and a higher yield to failure compared with the conventional 4.5mm cortical screw. Osteotomies were simulated in paired medial PSBs of seven horses and repaired with the 3.5mm BSF or the 4.5mm cortical screw. Repaired limbs were secured to a servohydraulic MTS and loaded in axial compression under a single cycle to failure. Load-deformation data was obtained to calculate stiffness, yield, construct failure and ultimate failure. Videography was used to qualify failure and gap displacement characteristics. There were no differences in construct stiffness (P = 0.68), yield (P = 0.81), construct failure (P = 0.15) or ultimate failure (P> 0.99) loads between groups. At construct failure, gap displacement was significantly greater at the abaxial aspect than the axial aspect of the PSB for BSF (P = 0.015) and AO (P = 0.015) specimens, and there was no difference between constructs (P = 0.81). Similar failure characteristics were observed between constructs, and only BSF screws exhibited bending. Ex vivo testing conditions do not perfectly replicate the speed and loading conditions in vivo. The BSF has similar biomechanical properties to the 4.5 mm cortical screw, however consistent deformation of the BSF must be considered with clinical use.
