The comparative biomechanical, histologic, and radiographic analysis of canine lumbar discs treated by surgical excision or chemonucleolysis.

Previous experimental studies on the canine intervertebral disc treated with chemonucleolysis have shown encouraging results in preserving normal histologic, biomechanical, and radiographic disc appearance. These observations suggest that chemonucleolysis may have significant advantages over surgical disc excision in preserving normal function of the lumbar vertebral motion segment. An experimental canine study was devised to examine and compare the short and long-term effects of chemonucleolysis and surgical disc excision on the entire lumbar motion segment to determine if one treatment modality is superior to the other in providing better maintenance of motion segment function. Twenty adult beagle dogs underwent anterior laparotomy. In ten dogs, Chymodiactin was injected into the L4-5 disc and in the remaining ten, routine surgical discectomies were performed on the L4-5 disc. Preoperative and presacrifice lateral radiographs were obtained. All dogs were allowed to exercise freely. Five dogs that received Chymodiactin (Group A) and five dogs that had surgical excisions (Group B) were killed six weeks postoperatively. Five months postoperatively, five dogs given Chymodiactin (Group C) and 5 having surgery (Group D) were also killed. Mechanical testing was performed on each treated disc sample with a modified MTS machine (MTS Systems Corp., Minneapolis, MN). Axial compression, bending, shear, and torsion were assessed in ten modes. Stiffness values for each mode were calculated. Following the biomechanical tests, the facet joints and the disc with the adjacent endplate were removed intact and analyzed histologically and with high resolution radiography. Six-week biomechanical testing revealed a 50% loss of torsional stiffness, as well as loss of anterior and medial-lateral shear stiffness in the chemonucleolysis group.(ABSTRACT TRUNCATED AT 250 WORDS)