Experimental Study Of The Combined Bone Graft Of β-calcium Tricalcium/α-calcium Sulphate Hemihydrate In Treating With Sheep Vertebral Body Defect

【Objective】To determine the bone formation ability and the Biomechanics in different stages in treating with sheep vertebral body defect model with the combined bone graft Gene-X which is mainly composed ofβ-calcium tricalcium /α-calcium sulphate hemihydrate.【Methods】Twenty-four adult sheep were operated on left retroperitoneum approach and the cavities were made in L2. L3. L4 and L5, Gene-X was transplanted into two cavities in random order, then one of the remaining cavities was randomly filled with PMMA, the other one was unfilled. Then these sheep were split into 4 groups. All the six sheep in each group were killed at 0 week, 8 weeks. 16 weeks and 36 weeks postoperation. The specimens of four sheep were subjected to micro-CT analysis, following micro-CT analysis, the explanted vertebrae will be submitted for histological analysis using undecalcified histology stained with haemotoxylin and eosin (H&E) staining and un-decalcified sections stained with Van-Gieson staining. The microcosmic changes of bone-material interface was observed and analysised. Biomechanical testing was performed on the specimens harvested from the other 2 sheep, with which the strength and stiffness were determined and analysised.【Results】Abservation with micro-CT: the surface of Gene-X and trabecular bone was blurred. The trabecular bone has been partly grown into the cement at 8 week and completely at 16 weeks. However, the trabeculae was still disorganized at 16 weeks. After 36 weeks, trabecular bone remodeling has been completed and no significant difference was found compared with the surrounding trabecular bone. Whereas, there was no significant difference existed in PMMA group among different stages. In control group, trabecular bone gradually grew into the cavities but never Complete regeneration. Histologically, Gene-X contacted the bone directly and absoption and the a trabecular bone has been partly grown into the cement at 8 weeks postoperation. The velocity on bone ingrowth and absorption accelerated at 16 weeks postoperation and the trabecular bone was more dense than the surounding, at 36 weeks, Gene-X has been basically been absorbed and trabecular bone remodeling completed. There is a gap between PMMA and bone and some of membrane structure was filled up it, no new bone formation on the surface. Biomechanical testing showed that the strength and stiffness among groups was as below: PMMA group> Gene-X group> control group at 0 week (P<0.05) and no significant difference existed at the following weeks (P>0.05).【Conclusion】Gene-X synthetic bone graft material has satisfactory bioactivity and osteoconduction. Besides, biomechanical fuciton of vertebrae is maintained during the procedure. It may become a new kind of vertebral augmentation filler material as a subsitute of PMMA.