Lumbar Interbody Fusion With A New BCP/CSH/SF/rhBMP-2 Composite In Sheep: An Experimental Study

[Objective] Through the preparation of injectable biphasic calcium phosphate/ calcium sulphate hemihydrate/silk fibroin/recombinant human bone morphogenetic protein-2(BCP/CSH/SF/rhBMP-2) composite materials, and do some experimental study of interbody fusion, the degradation and biocompatibility in vivo.[Methods] Eight sheep were randomly divided into two groups. Four sheep in each group were operated on left retroperitoneal approach and intervertebral discs of L1/2, L3/4 and L5/6 were exposed. Cavities were made on the midpoint of disc space perpendicular to sagittal plane, with 12 mm in depth and 7 mm in diameter. The opposite side of annular fibrosus was kept intact, nucleus pulposus was cleared completely, and endplate was processed to capillary hemorrhage. Three fusion sites in each animal were randomly assigned three treatments of four: biphasic calcium phosphate/calcium sulphate hemihydrate/silk fibroin(BCP/CSH/SF),biphasic calcium phosphate/calcium sulphate hemihydrate/recombinant human bone morphogenetic protein-2(BCP/CSH/rhBMP-2),biphasic calcium phosphate/calcium sulphate hemihydrate/silk fibroin/recombinant human bone morphogenetic protein-2 (BCP/CSH/SF/rhBMP-2) or autogenous iliac crest cancellous bone. sheep of the two groups were killed at 3 and 6 months postoperation respectively. The fusion sites were observed and analyzed by manual palpation, CT scan, undestructive biomechanical test, undecalcified histology, and histomorphology.[Results] All the bone subsitutes were injected successfully while the iliac cancellous bone couldn't be injected by syringe. The structures of all the lumbar spine specimens were presvered integrity with favorable stability and without appendix destroyed. The opposite side of annular fibrosus was kept intact and no leakage of bone substitutes was observed in the drilling side. The fusion rates of BCP/CSH/SF,BCP/ CSH/rhBMP-2,BCP/CSH/SF/rhBMP-2 and autogenous iliac cancellous bone assessed by manual palpation at 3 months and at 6 months postoperation, the fusion rates had no significant differences (P>0.05) . Respectively, the fusion stiffness of all directions among the three materials had significant differences (P<0.05) at 3 months postoperation. Statistical differences were not detected between BCP/CSH/SF and intact specimen (P>0.05). It revealed similar stiffness between iliac bone and BCP/CSH/SF/rhBMP-2 at 6 months after surgery (P>0.05). The similar stiffness of the two materials were greater than BCP/CSH/SF (P<0.05). The new bone formation among the three materials had significant differences (P<0.05) at 3 months postoperation. The residual volume of calcium phosphate has significant differences (P<0.05) among the two bone substitutes. It revealed almost new bone formation between iliac bone and BCP/CSH/SF/rhBMP-2 at 6 months after surgery (P>0.05). The similar bone formation volume of the two materials were more than BCP/CSH/SF (P<0.05). It showed the same tendency about residual volume of calcium phosphate with at 3 months postoperation.[Conclusion] The sheep anterior lumbar intervertebral fusion model, of which the cavities are made on sheep intervertebral space with 12 mm in depth and 7 mm in diameter, is an ideal fusion model to evaluate the capability of bone formation for injectable bone subsidies. The BCP/CSH/SF/rhBMP-2 composite artificial bone has good biocompatibility and biodegradability; construction of engineering artificial bone has a good repair of bone defects and interbody fusion and will be expected to become a new bone repair materials.