Effect of anterior cervical discectomy and fusion on adjacent segments in rabbits

This study is to investigate the effect of anterior cervical discectomy with internal fixation and fusion at different levels on adjacent segments in rabbits. Sixty New Zealand rabbits were randomly divided into four groups, one control group and three model groups, with 15 in each group. Each group underwent anterior cervical internal fixation and fusion at C3-4, C4-5, and C5-6 levels respectively. X-ray film was examined three, six and nine months after fusion to observe the changes in intervertebral space and endplate of adjacent segment. Immunohistochemistry was utilized to evaluate the effects of different fusion methods on adjacent segments of spine. As time went by, in model groups, the majority of cartilage endplates were calcified, as examined by X-ray. Immunohistochemical results of the intervertebral disc showed that the expression levels of collagen type II in nucleus pulposus were decreased significantly, while the expression levels collagen type I in annular fibrosus were increased. And collagen type I tends to replace collagen type II gradually in nucleus pulposus as time goes by. The change in collagen between upper and lower adjacent segments at C3-4 and C4-5 showed no statistical significance after fixation and fusion (p > 0.05). But for C5-6, the change showed statistical significance (p < 0.05). Cervical internal fixation and fusion can induce intervertebral disc degeneration of adjacent segment in rabbits, and cervical internal fixation and fusion operated at different levels may result in different effects on adjacent segments of cervical intervertebral disc.