Augmentation Of Sheep Vertebral Defect With BCP/CSH/SF/rhBMP-2: An In Vivo Study

【Objective】To evaluate the feasibility of BCP/CSH/SF/rhBMP-2 composites in the augmentation of sheep vertebral defect.【Methods】Six adult sheep were operated on left retroperitoneum approach and cavities were made in L2, L3, L4 and L5. BCP/CSH/SF, BCP/CSH/SF/rhBMP-2, and PMMA were transplanted to three cavities at random order respectively. The last cavity was unfilled served as negative group. Three sheep were killed at 3- and 6-month-time point postoperation, respectively. First of all, all the specimens received radiological examination and subsequent biomechanical testing. The strength and stiffness were determined on vertebrae with L1 as a control. Then the specimens were subjected to un-decalcified sections and stained with Van-Gieson method. The microcosmic changes of bone-material interface were observed, and the mount of new bone formation and cement residue were evaluated by histomorphometric analysis.【Results】Radiological examination showed that densities of both BCP/CSH/SF vertebrae and unfilled vertebrae were lower than normal vertebrae 3 months after injection. However, only the density of unfilled vertebrae was lower than normal vertebrae 6 months after injection. Density of PMMA vertebrae was higher than the normal vertebrae at the two different intervals. Density of BCP/CSH/SF/rhBMP-2 vertebrae was the same as the normal vertebrae at the two different intervals. Biomechanical testing showed that the compressive strength and stiffness of BCP/CSH/SF group were lower than BCP/CSH/SF/rhBMP-2 group, PMMA group, and intact group, and higher than unfilled group at 3 months after operation(P<0.05). At 6 months after operation, there was no significant difference of the compressive strength and stiffness in BCP/CSH/SF/rhBMP-2 group, BCP/CSH/SF/rhBMP-2 group, PMMA group, and intact group (P>0.05). All of them were higher than unfilled group (P<0.05). The compressive strength and stiffness of BCP/CSH/SF group enhanced at 6 month compared with 3 month, while PMMA obtained the opposite result. Histologically, in BCP/CSH/SF group, new bone was formed at the edge of composite at 3 month postoperation. The material was divided by new trabecular bone. Huge amounts of material was still unabsorbed. However, a large amount of material was replaced by new bone at 6 month postoperation. In BCP/CSH/SF/rhBMP-2 group, abundant new trabecular bone was formed in the center and at the edge of composite at 3 month postoperation. In addition, woven bone was observed in some area of the defects. 6 months after operation a small amount of residual implanted material remained in defects and bone repair of defects was basically finished. Connection of PMMA and bone was loosened. The cavity in unfilled group was present at two intervals. Bone histomorphometric examination showed that there was significant difference of the mount of new bone formation and cement residue between BCP/CSH/SF group and BCP/CSH/SF/rhBMP-2 group at the two different intervals (P<0.05).【Conclusion】The results indicate that BCP/CSH/SF/rhBMP-2 composites have satisfactory biocompatibility, osteoconduction, osteoinduction, and coordination between the cement degradation and the bone formation. In addition, biomechanical function of vertebrae is maintained during the procedure. The BCP/CSH/SF/rhBMP-2 composites may become a new kind of vertebral augmentation filler material as a subsitute of PMMA.