The Observation Of Nano-hydroxyapatite/collagen Composite Implants In Lumbar Intertransverse Process Fusion In Rabbits

OBJECTIVEThe aim of this study is to observe the characteristic and mechanism of osteogenesis of nano-hydroxyapatite/collagen composite in lumbar intertransverse process spinal fusion in rabbits. The results can be used for further clinical application.MATERIALS AND METHODSL5~6 single-level intertransverse process spinal fusion were performed in sixty-four female adult New Zealand white rabbits ,with 2.5ml bone or materials.The rabbits were randomly assigned to one of four groups based on the graft material they received, each group mcluding 16 rabbits: (l)autogenous cancellous bone group(ACB),(2) nano-hydroxyapatite/collagen composite group(Nano-HAC), (3) autogenous cancellous bone combined with nano-hydroxyapatite/collagen composite group(ACB+Nano-HAC),(4)nano-hydroxyapatite/collagen composite combined with recombinant human bone morphogenetic protion-2 group(Nano-HAC+rhBMP-2). Rabbits were euthanised at 2,4,6,1 Oweeks .The spine were excised and the fusion were analyzed by radiograms, manual palpation, uniaxial tensile mechanical testing and non-decalcified histology.RESULTSThe X-Ray finding presented the bony fusion in 4 rabbits at 6vveeks and 5 rabbits at 10 weeks in the ACB group. In the ACB+Nano-HAC group,the fusion was found in 3 animals at 6 vveeks and 4 at l O vveeks. Because of the special presentations of Nano-HAC and ACB on X-ray film,the results of these materials were evaluated by contmuous high density image. None excellent was found in Nano-HAC group. In the Nano-HAC+rhBMP-2 group, excellent cases were shovved l rabbit at 4 weeks,5 at 6 weeks and 6 at 10 vveeks.The manual palpation results shovved solid fusion in l é‘‘æ­Ÿ at 4 vveeks , 4 cases at 6 vveeks and 4 cases at 10 vveeks m the ACB group.None fusion was found in Nano-HAC group.In the ACB+Nano-HAC group,the solid fusion vvas revealed in 3 cases at 6 vveeks and 3 cases at 10 vveeks. In the Nano-HAC+rhBMP-2 group ,fusion was found in 4 at 6 weeks,5 at 10 vveeks. Unlaxial tensile biomechanical testing shovved similar stiffness in ACB,ACB+Nano-HAC and Nano-HAC +rhBMP-2 groups(p>0.05).In Nano-HAC group,the stiffness was significanted vveaker than those of the above 3 groups(p<0.01).In the ACB group,the fusion was mainly by membranous bone formation.In Nano-HAC group,Nano-HAC particles were swallowed,degradated and involved in the process of osteogenesis at early stage.In ACB+Nano-HAC group,ACB still presented membranous bone formation and did not promote the osteogenesis of Nano-HAC. There were much new bone matrix formed at 2 vveeks in Nano-HAC+rhBMP-2 group.At 6 and l O weeks,large pieces of mature bone matrix were found.CONCLUSIONSl. The nano-hydroxyapatite/collagen composite is a good bone graft substitutes with fast biodegradability,good bone compatibility,effective osteoconductivity and easy to be used for osteogeneis.2.Nano-HAC has similar structure to bone,but it just has osteoconductivity vvithout bone growth factors and osteogenetic cells.Its osteoinduction is not good as Nano-HAC combined with rhBMP-2 and ACB.3.1n ACB+Nano-HAC group,the fusion were reached mamly by ACB.No evidence shows that the 2 materials promote each other,but the antagonistic action is not found either.4. Nano-HAC has excellent ability to combmed with rhBMP-2,rhBMP-2 makes Nano-HAC easier to be degradation,utilized in osteogenesis. The osteogenesis is equal to that of ACB when Nano-HAC combined with rhBMP-2.