腰椎间盘人工髓核植入对软骨终板应力分布的影响

Effect of prosthetic nucleus pulposus replacement on stress distributions of lumbar disc endplate

目的测量腰椎间盘人工髓核植入后软骨终板应力分布的变化情况。方法选用新鲜成人尸体腰椎标本6具，Modic分级均为正常。采用MTS材料测量系统进行轴向垂直加载试验，通过压力传感器测量在正常状态、摘除髓核状态和人工髓核植入状态下L4-5椎间盘下终板各测量点的应力分布。结果正常椎间盘状态下，软骨终板应力分布在中心区域最高，沿两侧逐渐均匀减低。摘除髓核后终板应力分布变化显著，中心区域测量点的终板应力降低（P〈0．05），而纤维环部应力增高（P〈0．05）。人工髓核植入后，中心区域测量点应力分布明显增高，较正常状态增高15．1％（P〈0．05），且邻近区域亦出现高测量值。结论腰椎间盘人工髓核植入后，假体区域终板出现应力集中。目前假体设计尚不能在植入后完全达到正常的生物力学状态。

Objective To determine the stress distribution on endplate after lumbar prosthetic disc nucleus （PDN） replacement. Methods Six fresh lumbar vertebrae with normal Medic classification were harvested. The specimens were used to establish L4-5 intact, nucleotomy, prosthetic nucleus pulposus replacement models. Vertical compression tests were performed with MTS machine at the rate 50 N per second to maximum load of 1300 N. The stress under the endplate were measured directly with accurate pressure sensors. Results For intact specimens, the stress on the endplate maintained higher in the central zone of the endplate, and decreased gradually to the periphery, and was well-distributed. After nucleotomy, the stress on the central zone of endplate was significantly decreased, and increased stress occurred in the periphery of endplate. After PDN replacement, the stress on the central zone of endplate was found more 15.1% higher than that in intact disc （ P 〈 0. 05 ）, and the neighboring zone also showed higher stress measurements. Conclusions After lumbar prosthetic disc nucleus replacement, the stress concentration on endplate may occur in the central zone of prosthetic disc nucleus insertion. Therefore, the prosthetic nucleus pulposus with suitable shape, proper biomechanical functions and updated materials need further study.