BIOMECHANICS OF THE THORACOLUMBAR VERTEBRAL COLUMN OF DOGS DURING LATERAL BENDING

Objective-To study biomechanical characteristics of the normal and sur gically altered canine thoracolumbar vertebral column to determine the effects of surgery and trauma on lateral stability. Animals-The T13-L 1 vertebral motion units of 48 mixed-breed dogs were dissected free of surrounding musculature and prepared for biomechanical testing by cro ss-pinning the vertebral bodies and mounting in poly methylmethacrylat e. Procedure-Normal and surgically altered spinal specimens were subje cted to lateral bending. The mean slope of the bending moment versus a ngular displacement curve and the load to failure were compared betwee n treatment groups and significance was determined by the method of le ast squares (P < 0.05). Specimens were surgically altered by facetecto my, lateral fenestration, diskectomy, and combinations of these proced ures. Each specimen was subjected to lateral bending to failure at a r ate of 2.5 cm/min in a swing arm bending jig designed to simulate 4-po int bending and subject the specimen to pure bending. Results-Only spe cimens undergoing diskectomy had a significant decrease in slope and l oad at failure. Unilateral and bilateral facetectomies and fenestratio n induced a nonsignificant decrease in stiffness, compared with contro l specimens. Conclusions-Fenestrations and facetectomies do not appear to increase the risk oi injury to the canine thoracolumbar spinal cor d during lateral bending. Clinical Relevance-Fenestrations and facetec tomies, as used in routine laminectomies, may be performed without con cern for significant destabilization of the spine in lateral bending; however, it is possible that thoracolumbar spinal fractures involving only the vertebral body may significantly destabilize the spine in ail modes of bending.