丝素蛋白增强型磷酸钙复合rhBMP-2用于绵羊腰椎椎体间融合的实验研究

Experimental study on lumbar interbody fusion with silk fibroin enhanced calcium phosphate cement composite loaded with recombinant human bone morphogenetic protein-2 in sheep

目的评价可注射丝素蛋白增强型磷酸钙（silk fibroin／calcium phosphate cement，SF／CPC）复合人重组骨形态发生蛋白．2（recombinant human bone morphogenetic protein-2，rhBMP-2）应用于绵羊腰椎椎体间融合的效果。方法24只绵羊均建立L1,2、L3,4和L5,6前路椎体间融合模型。每只绵羊的3个腰椎间隙随机植入SF／CPC、CPC／rhBMP-2、SF／CPC／rhBMP-2和自体髂骨中的3种。分别于术后6个月和12个月各处死12只绵羊。每个时段均获得36个腰椎手术节段，每种材料9个节段。通过大体观察、手触检测、CT扫描、非破坏性生物力学测试和组织学观察分析脊柱融合状况。结果术后6个月时，手触检测SF／CPC、CPC／rhBMP-2、SF／CPC，rhBMP．2以及髂骨的融合率分别为0、33．33％（3，9）、55．56％（5，9）和77．78％（7，9）；12个月时为11．11％（1，9）、44．44％（4／9）、77．78％（7／9）和77．78％（7，9）。生物力学显示6个月时，前屈、后伸、左屈和右屈的融合刚度：髂骨〉SF／CPC／rhBMP-2〉CPC／rhBMP-2〉SF／CPC；12个月时SF／CPC／rhBMP_2刚度与髂骨相近，SF／CPC最小。组织学定量表明：6个月时，髂骨新生骨量〉SF／CPC，rhBMP，2〉CPC／rhBMP-2〉SF／CPC；而钙磷残留量依次增多；12个月时，SF／CPC／rhBMP-2新生骨量与髂骨相近；SF／CPC最少；钙磷残留量依次增多。结论SF／CPC／rhBMP-2人工骨具有骨传导和骨诱导性，降解与成骨能力匹配，是一种理想的脊柱融合材料。

Objective To evaluate the osteogenic characteristics of an injectable silk fibroin （SF） enhanced calcium phosphate cement （CPC） eomposite loaded with recombinant human bone morphogenetic protein-2 （rhBMP-2） on lumbar interbody fusion in sheep. Methods Twenty-four mature sheep were randomly divided into two groups. Each sheep underwent L1,2, L3,4 and L5,6 lumber interbody fusion, and the three disc spaces were randomly implanted with three of the following materials： SF/CPC, CPC/rhBMP-2, SF/CPC/rhBMP- 2 and autogenous iliae crest bone. One group was killed at 6 months and the other at 12 months. The fusion segments were observed and analyzed by manual palpation, CT scan, undestructive biomechanical testing, undecalcified histology, and histomorphology. Results The fusion rates of SF/CPC, CPC/rhBMP-2, SF/CPC/ rhBMP-2 and autogenous bone assessed by manual palpation were O, 33.33%, 55.56% and 77.78% respectively at 6 months. At 12 months, the fusion rates improved to 11.11%, 44.44%, 77.78% and 77.78%, respectively. The biomechanical results showed that fusion stiffness was significantly greater in autograft compared with SF/ CPC/rhBMP-2, CPC/rhBMP-2, and SF/CPC in 4 degrees of freedom （flexion, extension, right bending, and left bending） at 6 months. The SF/CPC/rhBMP-2 composite showed similar stiffness as autograft, which was signifi- cantly greater than CPC/rhBMP-2 and SF/CPC at 12 months. Both CPC/rhBMP-2 and SF/CPC/rhBMP-2 showed significantly greater stiffness at 12 months compared with that of at 6 months. The results showed that bone volume was significantly greater in autograft compared with SF/CPC/rhBMP-2, CPC/rhBMP-2, and SF/CPC at 6 months. There was significant difference among ceramic residue among SF/CPC, CPC/rhBMP-2 and SF/CPC/ rhBMP-2, with SF/CPC the greatest and SF/CPC/rhBMP-2 the least. At 12 months, the bone volume of SF/CPC/ rhBMP-2 composite was comparable with autograft, and greater than that of CPC/rhBMP-2 and SF/CPC. The bone volume of SF/CPC, CPC/rhBMP-2 and SF/CPC/rhBMP-2 was significantly greater at 12 months than that of at 6 months. The ceramic residue of SF/CPC, CPC/rhBMP-2 and SF/CPC/rhBMP-2 were significantly decreased. Conclusion The SF/CPC/rhBMP-2 composite had excellent osteoconduction and osteoinduction, and balanced degradation and osteogenesis, which may be a kind of ideal bone grafts in spinal fusion.