Recovery of Pelvic Limb Function in Dogs following Acute Intervertebral Disc Herniations

Chondrodystrophoid breeds of dog are prone to explosive herniation of mineralized disc material into the thoracolumbar spinal canal. The resulting acute spinal cord injury may respresent an excellent spontaneous model of acute traumatic spinal cord injury. The aims of this study were to quantify the recovery of dogs following acute disc herniations, to evaluate external factors that influence recovery, and to identify a group of dogs suitable for use in clinical trials on neuroprotective drugs. The gait of 88 dogs with thoracolumbar disc herniations was scored at the time of injury and 2, 4, and 12 weeks after surgical decompression. Dogs were placed into four groups dependent on the severity of presenting signs; dogs in group 1 had the most severe injury severity. Group 1 dogs showed a variable but incomplete recovery by 12 weeks. Dogs in groups 2 and 3 recovered uniformly but more completely, while dogs in group 4 made a rapid and excellent recovery and were deemed unsuitable for clinical trials. Combining dogs in groups 1, 2 and 3 produced a population of dogs with incomplete recovery by 12 weeks. Power analysis revealed that 87 such dogs would be needed per treatment group to detect a 20% change in function with a power of 95%. The number needed reduced drastically to 19 by eliminating dogs in group 1, but this produced less room for functional improvement. External factors did not appear to influence outcome. We conclude that dogs with spontaneous disc herniations provide a useful model of acute spinal cord injury for clinical trials.