An in vivo model of degenerative disc disease

Although the precise etiology of low back pain is disputed, degeneration of the intervertebral disc is believed to play an important role. Many animal models have been described which reproduce the changes found in degenerative disc disease, but none allow for efficient, large-scale testing of purported therapeutic agents. The purpose of this study was to develop a simple animal model resembling degenerative disc disease using the intervertebral discs found in the tails of rats. The proximal two intervertebral discs in the tails of 20 rats were injected with either chondroitinase ABC or control (phosphate buffered saline, PBS). The tails were harvested at 2 weeks, and measurements were made of intervertebral disc height (measured radiographically and histologically), biomechanics (stiffness, hysteresis, and residual deformation), and histologic appearance. Treatment with chondroitinase ABC resulted in a significant loss in intervertebral disc height (radiographic intervertebral disc height, p=0.001; histologic intervertebral disc height, p<0.001) and significant increases in all biomechanical parameters (stiffness, p<0.001; hysteresis, p=0.006; residual deformation, p=0.004) compared to PBS controls. Intervertebral discs treated with chondroitinase ABC had significantly lower histologic grades for each grading category (nucleus pulposus (NP), annulus fibrosus, and proteoglycan staining) compared to controls. The results of injury with chondroitinase ABC were similar to the findings in degenerative disc disease: reduced intervertebral disc height, diminished proteoglycan content, loss of NP cells, and increased stiffness of the disc. Thus, the model appears to be a reasonable tool for the preliminary in vivo evaluation of proposed treatments for degenerative disc disease.