OBJECTIVETo observe the effect of calcitonin on the pathology of fusion in lumbar posterior/facet spinal fusion in rabbit model.

METHODSThirty-two male New Zealand white rabbits were used to establish spinal fusion model. Sixteen rabbits received calcitonin at a dose of 1 IU x kg(-1) x d(-1) were classified as calcitonin group, and the remaining 16 rabbits as control group. Rabbits were killed 1, 2, 4, and 8 weeks after operations. Haematoxylin-eosin staining was applied to observe the pathological process of spinal fusion. Expression of bone morphogenetic protein-2 (BMP2) was detected by immunohistochemistry.

RESULTSBone resorption and fibrovascular stroma formation were the main histological presentation 1 week after surgery. Two and 4 weeks after surgery, more cartilage formed with varying degrees of mineralization, while less trabeculae could be observed in the phase of active bone formation. No remarked margin was seen between cartilage and bone tissues. Eight weeks after surgery, trabeculae distributed widely. The pathological process of spinal fusion in calcitonin group was faster than in control group. Emery scores showed significant differences at different time points (F = 265.44, P < 0.001). Calcitonin and time had a positively synergistic effect on Emery scores, and calcitonin caused significant difference in terms of Emery scores since the second week (F = 22.43, P < 0.001). Expressions of BMP, were significantly different at different time points (F = 1186.54, P < 0.001). Also, calcitonin and time had a synergistic effect on BMP2 expression (F = 13.14, P < 0. 001).

CONCLUSIONSEndochondral ossification exists in the spinal fusion process and may be the main way of ossification. Calcitonin may stimulate the expression of BMP2 and thus accelerate the process of spinal fusion.