Posterior element strength six months postinjury in the canine cervical spine

In vivo and in vitro biomechanical studies from this research group revealed that acute differences in the range of motion of C4-C5 canine cervical spine injuries decreased over a 24-week healing period to approach control values. It could be inferred that the repair tissue replacing the injured posterior elements functionally returned the spine to normal. This study investigated the biomechanical properties of the healed tissue and the isolated adjacent posterior elements at each intervertebral level of these same specimens. Twenty-two animals underwent one of four procedures at the C4-C5 level: (a) sham procedure, (b) transection of the supra- and interspinous ligament, (c) laminectomy, or (d) laminectomy plus bilateral facetectomy of the inferior articular facets. Twenty animals survived the entire testing protocol. Twenty-four weeks after injury, destructive testing was performed on the isolated posterior elements in tension loading. The maximum load, elongation at maximum load, stiffness, and energy absorbed to the maximum load were measured. The posterior elements injured by all of the procedures behaved similarly across all experimental groups after 24 weeks of healing. A trend for decreased stiffness in the more extensive surgery groups was seen, but no statistically significant differences were found. This paralleled the results of prior in vivo and in vitro range-of-motion testing.