BIOMECHANICAL, RADIOLOGIC, AND HISTOPATHOLOGIC CORRELATIONS IN THE PATHOGENESIS OF EXPERIMENTAL INTERVERTEBRAL DISC DISEASE

Study Design. The desert sand rat, an animal model for spinal degenera tive disc disease, was studied for biomechanical, histologic, and radi ographic characteristics. Load deformation curves with peak force and force decay, hematoxylin-eosin-stained sections, and lateral radiograp hs were correlated. Objectives. The hypothesis that the subchondral bo ne response preceded or contributed to the degenerative disc disease s een in the desert sand rat was tested. Summary of Background Data. Int ervertebral disc disease spontaneously develops in the desert sand rat during its lifetime. Approximately 50% will have significant disc dis ease by age 18 months. Previous studies have found metabolic and histo logic changes associated with intervertebral disc degeneration in the sand rat. Methods. Desert sand rats were killed at 3-, 9-, 15-, and 18 -month intervals and tested in a Rheometrics Solid Analyzer with nonde structive step strain loading to obtain a load deformation curve. Radi ographs and histologic sections of each animal were compared. Peak for ce and force decay were analyzed by level and by age. Analysis of vari ance and Tukey's methods were applied to data. Results. There were no statistically significant differences in biomechanical data. No histol ogic changes were noted in the study groups up to 18 months of age. Ra diographic differences characterized by subchondral bony sclerosis wer e noted by 18 months of age. No trends were noted when radiographic gr ades were compared with force data. Conclusions. The absence of biomec hanical histologic changes in the intervertebral disc per se from 3 th rough 18 months, with radiographic changes in the subchondral bone, su pports the hypothesis that the earliest changes in intervertebral disc disease in this animal model are related to the subchondral bone resp onse.