持续动态压应力对骨折愈合时环氧合酶mRNA表达及愈合骨机械特性的影响

Effect of continuous dynamic pressure stress on cyclooxygenase mRNA expression,bone mass and mechanical properties during fracture healing process in rabbits

目的探讨持续动态压应力环境下骨折愈合时环氧合酶转录水平的变化以及愈合过程中机械性能的改变。方法新西兰兔行单侧肱骨干横断截骨,试验组以天鹅记忆接骨器内固定,在骨折端造成持续动态压应力,对照组以加压钢板内固定。分别于术后第3、7、14、21、28、56天时在骨折间隙内取材,行Real-timePCR研究。术后2、4、8、12周时另取肱骨标本用作骨密度和生物力学测试。结果环氧合酶-2(cyclooxygenase-2,COX-2)mRNA的表达量较骨折前显著上升,且试验组术后3～4周时明显高于对照组(P<0.05),生物力学结果则显示愈合4周和8周时试验组的弯曲刚度、扭转刚度、最大扭转和弯距均显著高于对照组(P<0.05),而此时试验组局部骨密度也相对较高(P<0.01)。结论天鹅记忆接骨器产生的持续动态压应力诱导了COX-2的转录,而COX-2mRNA的高表达则促进了成骨细胞的分化和骨痂矿物质的沉积,加速了骨折的愈合和机械性能的恢复。

Objective To explore the effect of continuous dynamic pressure on cyclooxygenase mRNA expression, bone mass and mechanical properties during experimental fracture healing. Methods Unilateral osteotomy of left humeral diaphysis was performed on adult New Zealand rabbits. The humeral fracture was fixed by shape memory connector （ SMC ） in Study Group and by 4-hole dynamic compression plate （DCP） in Control Group. Samples from the fracture gaps were obtained on day 3, 7, 14, 21,28 and 56 and the temporal expression patterns of cyclooxygenase mRNA during the healing process were examined by real-time PCR. The humeri were harvested and sent for biomechanical tests as well as dual-energy X-ray absorptiometry in 2, 4, 8 and 12 weeks postoperatively. Results The relative levels of COX-2 mRNA were elevated after fracture and were significantly higher in Study Group than in Control Group at 3 and 4 weeks postoperatively. The BMD values of the Study Group were significantly higher than those in the Control Group from 4 to 12 weeks postoperatively. With regard to bone mechanical parameters, the Study Group showed significantly higher maximum torque, torsional stiffness, bending strength and bending rigidity than those in the Control Group at 4 and 8 weeks postoperatively. Conclusion The persistent dynamic longitudinal pressure produced by SMC may accelerate bone healing with increased bone mass and bone strength after fractures in this rabbit model by promoting the proliferation activity of the osteoblasts and callus mineralization, which may be closely related with a higher COX-2 mRNA expression.