低弹性模量外固定系统对股骨干骨折模型的生物力学研究

Biomechanical effect of external fixation system with low-modulus of elasticity on femoral shaft fracture model

目的通过在模拟股骨上对不同弹性模量的外固定系统进行生物力学测试，探讨不同弹性模量外固定系统对股骨干骨折应力及其分布的影响。方法选择8套与人体股骨力学性质类似的玻璃钢制成股骨干骨折模型，在模型上分别安装Ti-24Nb-4Zr-7．9Sn（低弹性模量组，弹性模量为33GPa，4套）和Ti-6Al-4V（高弹性模量组，弹性模量为110 GPa，4套）钛合金半针，连接套夹和碳纤维外固定棒，在骨折断面、外固定半针以及钉道周围粘贴电阻应变计，分析局部应力，测量不同弹性模量外固定系统在同样载荷条件下骨折断面及钉道周围应力的大小和分布。结果在实验载荷条件下，随着载荷和力矩的增大，高弹性模量组与低弹性模量组骨折断端和钉道周围应力有不同程度增大。当侧压载荷为90N时，两组的侧压应变值分别为（6．5±3．5）×10^-56、（43．5±22．7）×10^-6；当侧压载荷为300N时，应变值为（16．5±0．7）×10^-6、（140．5±9．5）×10^-6.当弯曲载荷为1．6N·m时，两组的应变值分别为（0．3±0．5）×10^-6、（47．1±31．5）×10“；当弯曲载荷为11．0N·m时，应变值分别为（359．7±39．9）×10^-6、（453．5±29．0）×10^-6。当侧压载荷≥90N或弯曲载荷介于1．6～8．8N·m时，两组之间骨折断端应力应变值差异有统计学意义（P〈0．05）。在3种力学作用下，与高弹性模量组相比，低弹性模量组钉道局部应力分布更均匀，应力相对集中的针道局部应力变小。结论低弹性模量外固定系统有利于应力传导，更符合生物力学的要求，从而可能有效避免应力遮挡效应，促进骨折愈合。

Objective To explore the effects of external fixation system with various moduli of elasticity on the stress and its distribution at a femoral shaft fracture. Methods Glass fiber reinforced plastic （GFRP） which resembles human femur in mechanics was used to create 8 models of femoral shaft fracture. Four models were of low elastic modulus group in which the halfpins of the external fixation system were made of titanium alloy Ti-24Nb-4Zr-7.9Sn （E = 33 GPa） while the other 4 were of high elastic modulus group in which the external fixation system were made of titanium alloy Ti-6A1-4V （E = ll0 GPa） . Strain gages were mounted near the fracture plane, halfpin and pin track to detect the stresses and their distributions under the same load in the 2 external fixation systems of different moduli of elasticity. Results The stresses at the fracture end and around the pin track increased with an increase in the load and moment. When the lateral pressure load was not less than 90 N or the bending load ranged from 1.6 N · m to 8.8 N · m, the differences in the stress at the fracture end were significant between the 2 groups （ P 〈 0.05）. In 3 kinds of operating modes, the low elastic modulus group showed more symmetrical distribution and less stress concentration around the pin track. Conclusion Since external fixation system of low elasticity modulus may be better in stress transmission and distribution, it can reduce the effect of stress-shielding and accelerate bone-healing.