A Nonlocking End Screw Can Decrease Fracture Risk Caused by Locked Plating in the

Background: Locking plates transmit load through fixed-angle locking screws instead of relying on plate-to-bone compression. Therefore, locking screws may induce higher stress at the screw-bone interface than that seen with con-ventional nonlocked plating. This study investigated whether locked plating in osteoporotic diaphyseal bone causes a greater periprosthetic fracture risk than conventional plating because of stress concentrations at the plate end. It further investigated the effect of replacing the locked end screwwith a conventional screw on the strength of the fixation construct. Methods: Three different bridge-plate constructs were applied to a validated surrogate of the osteoporotic femoral diaphysis. Constructs were tested dynamically to failure in bending, torsion, and axial loading to determine failure loads and failuremodes. A locked plating construct was compared with a nonlocked conventional plating construct. Subsequently, the outermost locking screw in locked plating constructs was replaced with a conventional screw to reduce stress concentrations at the plate end. Results: Compared with the conventional plating construct, the locked plating construct was 22 % weaker in bending (p = 0.013), comparably strong in torsion (p = 0.05), and 15 % stronger in axial compression (p = 0.017). Substituting the locked end screw with a conventional screw increased the construct strength by 40 % in bending (p = 0.001) but had no significant effect on construct strength under torsion (p = 0.22) and compressive loading (p = 0.53) compared with the locked plating construct. Under bending, all constructs failed by periprosthetic fracture