双侧关节突联合棘突间植骨融合预防胸腰椎骨折术后矫正丢失的生物力学三维有限元分析

Biomechanical finite element analysis on bone graft fusion of bilateral articular process combined with spinous process to prevent postoperative correction loss after thoracolumbar fracture surgery

目的应用三维有限元技术构建腰椎双侧关节突联合棘突间植骨融合的生物力学新模型,评估其预防胸腰椎骨折术后矫正丢失机制,论证新模型是否比单纯双侧关节突植骨融合模型更具预防矫正丢失的优越性。方法选取青壮年男性人体脊柱标本一具,范围为L1～L2,构建骨折伴有椎间盘严重损伤的有限元力学模型,模拟患者术后内固定取出后的状态,建立双侧关节突联合棘突间植骨融合和单纯双侧关节突植骨融合的两种有限元模型,分析在压缩载荷、前屈与后伸力矩等组合作用下的椎间盘、上下终板、关节突植骨区、棘突间植骨区等的应力和位移。结果在压缩载荷和前屈与后伸力矩作用下,新融合模型的椎间盘竖向压缩位移和应变较原融合模型明显减小约为20%～35%,关节突植骨区应力也较原融合模型减小,减小量约为5.5%～13%,棘突间植骨区承担应力大幅增加,约增加了2.5～12.3倍,后柱承担内力比例明显增加。结论双侧关节突联合棘突间植骨融合后,脊柱承载结构主要由双侧小关节和棘突三点立体承担,后部棘突间植骨形成了新的强化张力带,增加了损伤节段的三维稳定性,有效减轻关节突植骨区应力集中程度,减小受损椎间盘的竖向应变和压缩位移,可预防胸腰椎骨折并伴有椎间盘严重损伤术后矫正丢失。

Objective To develop a biomechanical model of bone graft fusion of bilateral articular process combined with spinous process using 3D finite element method to explain its preventive role on postoperative correction loss after thoracolumbar fracture surgery, and to evaluate the effect on preventing postoperative correction loss better than that of bone graft fusion simply in bilateral facet joints. Method Computed Tomography （CT） scans were performed on L1-2 motion segment of the fresh spine specimen of an adult male cadaver, and mechanical model of functional spinal unit of L1-2 with vertebrae fracture affiliated disc serious damage were developed by defining injured material properties. From simulating dismantle internal fixation in patients who were dealt with bone graft fusion either of bilateral articular process combined with spinous process or simply in bilateral facet joints, two digitized surgical models were established by finite element method in Ansys 11.0 software platform. Four load conditions containing compression, antefiexion and retroextension were added on digital fusion models on the basis of three-column spine theory to compute stresses/strains in bone graft and endplates and compressive displacements in damaged discs. Result Under the action of compressive load, antefiexion moment or post extension moment, the vertical compressive displacement and strain of disc annulus fibrous of the new fusion model （FSF） reduced significantly by 20%-35% than those of the old one （FF）; and the stress level of bone graft of articular process also decreased about 5.5%-13%. The bearing capacity of the interspinous bone graft increased markedly up to 2.5-12.3 times, or more than that of and supra spinous ligaments. Conclusions After the fusions between the bilateral facet joint and the spinous process, the load bearing function of the spinal column is carried out mainly by three points of the spinous process and bilateral facets in three - dimensional space, and a new strengthening tension-band is formed by transplanted bone between spinous process. It can increase the three-dimensional stability of spinal segments, effectively relieve the stress concentration on the bone graft area of bilateral articular process, and reduce the vertical compressive strains and displacements of the acutely injured disc, which could prevent the loss of postoperative correction after thoracolumbar fracture surgery,