Nondestructive, fatigue cyclic, and ramped cyclic biomechanical testing of surgical techniques for stabilization of the lumbosacral junction in dogs

Abstract

Objective: To compare transarticular screw fixation (TSF), pedicle screw-rod fixation (PSRF), and screws and polymethylmethacrylate (SPMMA) for stabilization of the canine lumbosacral junction (LSJ). Study design: Ex vivo biomechanical study. Sample population: Twenty-one L7-S1 canine spine specimens collected from adult, large-breed dogs. Methods: Specimens were subjected to nondestructive biomechanical testing in flexion/extension (FE), lateral bending (LB), and axial rotation (AR). Subsequently, the L7-S1 joint was destabilized by dorsal laminectomy and partial discectomy of L7-S1 and then stabilized by (1) TSF, (2) PSRF, or (3) SPMMA (n = 7 specimens/group). Stabilized specimens were subjected to nondestructive biomechanical testing, fatigue cyclic testing, and ramped cyclic testing. For nondestructive and fatigue cyclic testing, range of motion (ROM) was calculated for each testing condition/stabilization method, while for ramped cyclic testing the bending moment necessary to reach a ROM of 5.0°, 7.5° and 10.0° and failure mode were recorded. Linear mixed models and Fisher's exact test were used to analyze continuous parameters and failure modes, respectively. Results: All stabilization methods resulted in an equal reduction in ROM in FE. Fatigue cyclic testing resulted in minor increases in ROM compared to baseline for all groups. Ramped cyclic testing resulted in failure of all groups, with no differences between groups for the bending moment necessary to reach 5.0°/7.5°/10.0° of ROM. The main failure mode for each method was progressive screw loosening. Conclusion: Transarticular screw fixation, PSRF and SPMMA provided immediate biomechanical stability to the LSJ and were similar when subjected to fatigue and ramped cyclic testing. Clinical significance: Transarticular screw fixation, PSRF, and SPMMA are biomechanically effective options for stabilizing the canine LSJ. This study supports clinical use of these procedures.