Roentgenographic and biomechanical analysis of lumbar fusions: a canine model.

An animal model of anterior and posterior column instability was developed to allow in vivo observation of bone remodeling and arthrodesis after spinal instrumentation. Various combinations of spinal fusions and instrumentation procedures were performed after an initial anterior and posterior destabilizing lesion was created at the L5-L6 vertebral levels in 35 adult beagles. After 6 months of postoperative observation, there was improved probability of achieving a spinal fusion if spinal instrumentation had been used. All biomechanical testing was performed after removal of instrumentation to test the inherent stiffnesses and quality of the spinal fusions. The fusions performed in conjunction with instrumentation (group V = Harrington instrumentation and posterolateral fusion; group VI = Luque instrumentation and posterolateral fusion) demonstrated the greatest axial rotation stiffnesses (group V, p less than .05); axial compressive stiffness (group V, p less than .05); and flexural stiffness (group VI, p less than .05). The results show that a spinal fusion can be more reliably achieved and will be more rigid if it is accompanied by spinal instrumentation.