腰椎峡部重建内固定器的设计及应用实验

DESIGN AND EXPERIMENTAL STUDY OF INTERNAL FIXATOR FOR THE RECONSTRUCTION OF LUMBAR ISTHMUS

目的探讨腰椎峡部重建内固定器治疗腰椎峡部不连的临床应用可行性及价值,为其临床应用奠定基础。方法取健康山羊16只,体重22.65～31.22kg,建立L5腰椎峡部不连动物模型。将动物随机分为2组,每组8只,分别为单纯植骨组(于峡部不连处单纯植入自体髂骨0.8～1.1g)和内固定植骨组(先安装内固定器再于峡部不连处植入自体髂骨0.8～1.1g)。于术后8周处死动物行影像学、大体和组织学观察。同时进行生物力学实验:取自愿捐赠椎体标本5个,来源于男4例,女1例;年龄35～51岁。于L5椎体左峡部横断,造成腰椎峡部不连模型。将微型位移传感器置于峡部断端,电子万能试验机模拟腰椎峡部重建内固定器施力方向,以2mm/min的速度匀速加载,用动态数据采集分析仪同步收集峡部断端的形变值。全部加载直至标本发生骨破坏,观察位移传感器是否发生形变及腰椎峡部断端处是否发生闭合。结果实验动物均无因手术原因造成的神经损伤或死亡,术后麻醉清醒后即活动,无伤口感染发生。术后8周腰椎双斜位X线片和大体观察均显示,内固定植骨组峡部融合率为100%,显著高于单纯植骨组的62.5%(P<0.05)。组织学观察示,单纯植骨组3只峡部未融合动物腰椎峡部断端骨小梁骨陷窝空虚,骨细胞消失;内固定植骨组峡部断裂处骨小梁连接成网状,小梁间为骨髓组织,骨小梁局部呈现不同程度的"镶嵌样"结构。椎体标本生物力学测试与数据处理结果显示,匀速加载过程中,当外载荷为40N时,位移传感器发生形变,腰椎峡部断端缝隙开始闭合;随着外载荷进一步加大,传感器位移呈线性上升趋势;当外载荷为212N时,位移传感器不再发生形变,腰椎峡部断端缝隙完全闭合,紧密接触,开始呈现加压效应。结论腰椎峡部重建内固定器具有明显的稳压和加压的双重力学功效,且融合率高。

Objective To investigate the clinical applicability and value of internal fixator for the reconstruction of lumbar isthmus in the treatment of lumbar vertebral spondylolysis and to lay a fundation for its clinical application. Methods Sixteen healthy goats weighing 22.65-31.22 kg were selected to establ ish the models of vertebral spondylolysis at L5, which thereafter were randomized into two groups （n=8）： bone graft group in which 0.8-1.1 g fresh autogenous bone was transplanted into the isthmus spondylolysis area, and internal fixation with bone graft group in which internal fixator was installed before transplanting 0.8-1.1 g fresh autogenous bone into the isthmus spondylolysis area. All animals were killed 8 weeks after operation to receive imaging, topographic anatomy and histology detection. Meanwhile, biomechanics test was performed by using 5 donated vertebral body specimens （4 males and 1 female aged 35-51 years old）. The left isthmus of L5 vertebra was transected to serve as lumbar vertebral spondylolysis model. A mini-displacement sensor was put at the transected ends of the isthmus. Then loading was conducted with a constant velocity of 2 mm/min by electronic omnipotent tester simulating the direction of fixation force of the internal fixator, and the deformation value of the transected ends was collected by a dynamic data collector and analyzer. The loading was continued until the vertebra specimens were damaged. The deformation of displacement sensor and the closure of transected ends of the lumbar isthmus were observed. Results All the goats behaved normally shortly after operation, and no nerve injury induced by operation and no wound infection occurred. Bilaterally obl ique X-ray films of lumbar vertebra and topographic anatomy 8 weeks after operation showed the fusion rate of the internal fixation and bone graft group and the bone graft group was 100% and 62.5%, respectively, indicating there was a significant difference （P 〈 0.05）. Histology observation showed 3 goats in the bone graft group presented empty bone trabecula, empty bone lacuna and the disappearance of osteocytes at the transected ends of lumbar isthmus; while in the internal fixation and bone graft group, the bone trabecula grew into cancellous structures with hematopoietic and fatty bone marrow tissue inside, and parts of the bone trabecula had various degrees of mosaic-l ike pattern. During the upload, the biomechanics test and data processing results showed when the external load was 40 N, the deformation of displacement sensor was identified and the gap between the transected ends of lumbar isthmus started to close; then with the increase of external load, the displacement sensor tended to ascend in a l inearity manner; while when the external load was 212 N, the displacement sensor had no further deformation, the gap between the transected ends of lumbar isthmus was completely closed, and the pressor effect appeared. Conclusion The internal fixator for the reconstruction of lumbar isthmus has mechanical effects of stabil izing and elevating pressure with a high fusion rate.