Comparison of locking and conventional screws for maintenance of tibial plateau positioning and biomechanical stability after locking tibial plateau leveling osteotomy plate fixation

Abstract

Objective - To compare locking screws with conventional screws inserted in the tibial plateau fragment for reduction and stability of the construct after tibial plateau leveling osteotomy (TPLO), using a locking TPLO plate. Study Design - Experimental biomechanical study. Animals - Cadaveric canine pelvic limbs (n=8 pairs). Methods - TPLO was stabilized with either conventional cortical screws or locking screws in a compressed osteotomy model. Titanium pins inserted into the tibial plateau and proximal metaphysis were used to track bone fragment location by computed tomography (CT) imaging. CT imaging was performed after osteotomy reduction, after plate stabilization, and after 30,000 cycles of axial compression testing. After 30,000 cycles, cyclic loading was continued with monotonically increasing peak-load until failure. Results - The magnitude of rotation about the sawing axis was significantly greater for the conventional screw group because of plate application (P=.009). Translational movement of the tibial plateau fragment toward the plate was significantly greater for the conventional screw group (P=.006). There were no significant differences between groups in stiffness or number of cycles to failure. Conclusion - Maintenance of tibial plateau position was significantly superior for the locking screw group during plate application; however, screw type had no effect on fixation stability under cyclic loading. Clinical Relevance - These results suggest that conventional screws and careful contouring of the TPLO plate can provide comparable mechanical stability to fixation with locking screws in the tibial plateau under load-sharing conditions, but potentially at the expense of osteotomy reduction. © Copyright 2008 by The American College of Veterinary Surgeons.