Kinematic Behaviour of a Novel Pedicle Screw-Rod Fixation System for the Canine Lumbosacral Joint

Objective: To determine the biomechanical behaviour of a novel distraction-stabilization system, consisting of an intervertebral distraction bolt, polyaxial screws and connecting rods, in the canine lumbosacral spine. Study design: Biomechanical study. Sample population: Cadaveric canine lumbosacral spines (L4-Cd3) (N=8) Methods: Cadaveric lumbosacral spines were harvested, stripped of musculature, mounted on a 4-point bending jig, and tested in extension, flexion and lateral bending using non-destructive compressive axial loads (0-150N). Angular displacement was recorded from reflective optical trackers rigidly secured to L6, L7 and S1. Data for primary and coupled motion were collected from intact spines; after destabilization at L7-S1, and following surgical stabilisation with the new implant system. Results: As compared with the intact spine, laminectomy resulted in a modest increase in angular displacement at L6-L7 and a marked increase at L7-S1. Instrumentation significantly reduced motion at the operated level (L7-S1) with a concomitant increase at the adjacent level (L6-L7). Conclusion: The combination of a polyaxial pedicle screw-rod system and intervertebral spacer provides a versatile solution of surgical stabilisation of the lumbosacral joint following surgical decompression in the canine lumbosacral spine. The increase in motion at L6-L7 may suggest the potential for adjacent level effects and clinical trials should be designed to address this question. Clinical relevance: These results support the feasibility of using this new implant system for the management of degenerative lumbosacral disease in dogs. The increase in motion at L6-L7 may suggest the potential for adjacent level effects and clinical trials should be designed to address this question.