[EXPERIMENTAL STUDY ON POLY-AMINO ACID/NANO-HYDROXYAPATITE/CALCIUM SULFATE CAGE FOR LUMBAR INTERBODY FUSION IN GOATS]

To evaluate the effect of poly-amino acid/nano-hydroxyapatite/calcium sulfate (PHC) Cage in lumbar interbody fusion of the goat.

Eighteen mature female goats (weighing 29-33 kg) were divided into 3 groups randomly: PHC Cage group (group A), titanium Cage group (group B), and ilium group (group C). A left extraperitoneal approach was used to establish the animal model of discectomy and interbody fusion with Cage or ilium. The general situation was observed for 24 weeks after operation. X-ray films were taken to measure disc space height (DSH) before operation and at 4, 12, and 24 weeks after operation. CT three dimensional reconstuction was performed at 24 weeks after operation to evaluate the interbody fusion according to modified Brantigan grading. The specimens of L3,4 were harvested for mechanical test, histological, and scanning electron microscope (SEM) observation at 24 weeks after operation.

All goats survived to the end of experiment. DSH at 4 weeks after operation increased when compared with preoperative one in each group, and then decreased; DSH was significantly lower at 12 and 24 weeks after operation than preoperative one in group C (P < 0.05). There was no significant difference in DSH among 3 groups at preoperation and 4 weeks after operation (P > 0.05); at 12 and 24 weeks after operation, DSH of groups A and B was significantly higher than that of group C (P < 0.05), but no significant difference was found between groups A and B (P > 0.05). CT three dimensional reconstuction showed that bony fusion was obtained in all goats of groups A and C, and in 3 goats of group B; according to modified Brantigan grading, the scores of groups A and C were significantlly higher than that of group B (P < 0.05), but no significant difference between groups A and C (P > 0.05). The biomechanical test showed that there was no significant difference in range of motion between group A and group B (P > 0.05), which were significantly lower than that of group C (P < 0.05). Microscopy and SEM observations showed that the interface between the Cage and vertebral body in group A was compact without obvious gap, and most conjunctive region was filled with osseous tissue; the interface was filled with soft tissue, and the connection was slack with obvious gap in some region in group B; the interface connection was compact, most region was filled with osseous tissue in group C.

The interbody fusion with PHC Cage is effective in goat lumbar interbody fusion model. The interface connection is compact between the Cage and the host bone followed by micro-degradation of PHC Cage, but the long-term degradation need further observation.