Experimental Study On Intertransverse Process Lumbar Fusion With RhBMP-2/AGS In A Rat Modal

Objective: This study was performed to investigate in SD rat model the feasibility of applying rhBMP-2/AGS composite as a graft substitute for autogenous bone in intertransverse process lumbar fusion. The purpose was to collect experimental evidence for further clinical application of rhBMP-2/AGS.Method: Fifty SD rats underwent intertransverse process lumbar fusion, with varied or without implants. Rats were randomly assigned into five experimental groups: A ) negative control (no graft implanted); B) autogenous iliac bone graft; C ) AGS alone; D) 50ng rhBMP-2/AGS composite;E)100ng rhBMP-2/AGS composite. The animals were killed 12 weeks after surgery. Resultant fusion masses were evaluated by gross inspection, manual palpation, radiography, biomechanical testing and histological examnation.Results:Either in autograft iliac bone group or 100ng rhBMP-2/AGS composite group, through gross inspection, fusion mass spanning between L4 and L5 transverse processes were both observed in 8 rats. Similar fusion mass were found in one rat of 50ng rhBMP-2/AGS composite group. No such structure was presented by rats of negative control and AGS alone group.Judged by manual palpation, 100ng rhBMP-2/AGS composite group and aotograft iliac bone group achieved equally 80% in fusion rate, indicating no statistical difference existed in between(P>0.05). Only 10% of 50ng rhBMP-2/AGS composite group had fusion. Fusion was not achieved in any rat of negative control or AGS alone group. The autograft iliac bone group and 100ng rhBMP-2/AGS composite group both exceeded the rest three groups in manual palpation(P<0.05). Radiography showed 80% spinal fusion rate was achieved in aotograft iliac bone group and 100ng rhBMP-2/AGS composite group. While 10% spinal fusion rate was achieved in 50ng rhBMP-2/AGS composite group. However,no fusion was showed in negative control or AGS alone group.Biomechanical analysis revealed that control group and AGS alone group were statiscally weaker than the rest three groups in tensile strength (P<0.05). The autograft iliac bone group and 100ng rhBMP-2/AGS composite group both exceeded 50ng rhBMP-2/AGS composite group in biomechanical strength(P<0.05).There was no statistical difference between autograft iliac bone group and 100ng rhBMP-2/AGS composite group in biomechanical analysis (P>0.05).A higher osteogenesis rate and more mature fusion was shown histologically in rats of 100ng rhBMP-2/AGS composite group than of all the other groups.Conclusions: The value of AGS as a carrier for rhBMP-2 was confirmed by this study. The implantation of Certain dosage of rhBMP-2/AGS composite promoted the intertransverse process fusion in rat and achieved similar results that were gained by autogenous iliac bone implantation, suggesting that rhBMP-2/AGS composite might be a promising substitute for autogenous bone graft.