| ObjectiveTo prepare the combined bone graft (COB) withβ- Tricalcium phosphate (β-TCP) andα-Calcium sulphate hemihydrates (α-CSH), to explore its setting performance of different composition ratios ofβ-TCP/α-CSH. To establish a rabbit multi-segments posterolateral arthrodesis of thoracic vertebrae and to explore the degradation and bone formation characters of COB and its effects of spinal fusion when used in the model.MethodsCalcium sulphate dehydrate (CSD) was dehydrated at given pressure and temperature to prepareα-CSH. Bovin cancellous turned to porous material that major components wasβ-TCP after being removed cells , defatted and sintered twice at given temperature. The porous particals ofβ-TCP that their diameters were 0.85—2mm were mixed with the ethanol suspension ofα-CSH powder that the quality was same asβ-TCP particals, afer being dried in 37℃oven, the COB particals had been prepared, then the composition and structures of them were determined via SEM and XRD. The setting times and setting strengthes of COB particals which have different components ratios ofβ-TCP/α-CSH were examined in vitro and the composition and structure changes of setted COB were then examined via SEM and XRD.The rabbit multi-segments posterolateral arthrodesis of thoracic vertebrae was established, the COB particals which components ratio ofβ-TCP/α-CSH is 7:3 were grafted at posterolateral of left part of vertebral plates, and local autografts (sipnal processes and vertebral paltes) wre grafted at right side as control. The aminals were sacrificed 4, 8 and 12 weeks after the operation. The fusion effect of thoracic vertebrae , the degradation of COB and the growth-in of new bone were studied via X-ray and Micro CT, and then further studied via histological methods, Mo-target soft X-ray and Tetracycline fluorescent imaging.ResultsTheα-CSH powder that was prepared at given pressure and temperature has a high purity and a regular crystal structure. The major component of porous particals, from which bovin cancellous were sintered twice, isβ-TCP, and the micro-structre of normal cancellous have been reserved in the particals. The COB with setting character can be prepared fromβ-TCP andα-CSH, and with ethanol as a media. The setting times of COB are shortened when the ratios of solid to liquid be heightened. At the same ratio of solid to liquid, the setting times are shortened, and the setting strenghth are heightened when the composition proportion ofα-CSH be heightened. When the ratio of solid to liquid is lg:0.2ml, the initial setting time of COB(CSH/TCP=3:7) is 4.9±1.3min, and final setting time is 14.7±3.4min, and its compressive strenghth is 7.32±1.27MPa 7 days after being setted, which can meet the clinical request.The result of X-ray shows that the fusion rate of COB lateral is 75% at 12 weeks after operation in the rabbit multi-segments thoracic arthrodesis, superior to the local autograft (spinal processes) lateral (54.4%). The result of Micro CT suggests that the fusion mass of COB lateral are stronger and larger than the autograft lateral at 8 and 12 weeks after operation, and at 12 weeks after operation, new bone surrounds the COBs and grows into the interior of COB scaffolds largely. The Bone Volume Fraction (BVF) of COB is 0.49±0.08 at 4 weeks after operation, only 0.16±0.05 at 12th week poster-operation, and the formation of new bone matches to the degradation of COBs. Mo-target soft X-ray shows that COBs are keeping to degradate after being grafted and are substituted by new bone. Histology suggests that the new bone formation has been seen at the outside and inside of scaffold of materials, COBs are keeping to degradate and substituted by the growth-in of new bone. The result of fluorescentgram shows that fluorescent materials deposite largely at the inside and outside of COBs, the result of Statistics suggests that the mineral deposition rate of new bone at COB lateral has no difference with the autograft lateral.Conclusion1. Combined bone graft can be prepared byα-CSH andβ-TCP using ethanol as a media, there is not same report in the world at present.2.The initial setting time of COB (CSH/TCP=3:7) is 4.9±1.3min and final setting time is 14.7±3.4min when the ratio of solid to liquid is 1g/0.2ml, and the compressive strength is 7.32±1.27MPa at 7th day after setting, which is meet the clinical request.3. The fuse rate of COBs in rabbits throcic multi-segments posterolateral arthrodesis model is superior to the situation of only the local bone (spinous processes) as autograft. The degration rate of combined bone graft matches the speed of new bone grow-in in the COB lateral.4. The bone formation of combined bone graft is evident in the rabbits multi-segments spinal fusion model . The mineralization speed of new bone in COBs can arrives to the level of autograft.
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