基于骨盆矢状位参数恢复强直性脊柱后凸矢状面平衡的生物力学分析

Biomechanical analysis of sagittal balance restoration of ankylosing kyphosis based on pelvic sagittal parameters

背景:强直性脊柱炎后凸主要表现为矢状位畸形,截骨角度是术前需要解决的关键问题之一,矫正角度不足以及矫正过度都可能造成脊柱矢状位的二次失衡。目的:应用计算机辅助软件建立强直性脊柱炎后凸三维有限元模型,基于骨盆矢状位参数设计个性化手术截骨方案恢复矢状面平衡,并分析其生物力学特性。方法:收集新疆医科大学第六附属医院1例强直性脊柱炎后凸住院患者C1至骶尾骨的CT数据,根据301分型确定后凸畸形为ⅢA型。将CT数据导入计算机建模软件中,建立强直性脊柱后凸畸形三维有限元模型,测量骨盆入射角、骨盆倾斜角数值,并通过骨盆入射角计算出理论骨盆倾斜角角度。设计两种不同截骨方案的模型,其中模型2使用肺门-髋轴测量方法(重建矢状面平衡)测量L3预截骨角度为32.2°,模型1则在未重建矢状面平衡下设置截骨角度为40°,在构建完成的两个模型上模拟去松质骨截骨术,并对截骨矫形后模型的钉棒系统、截骨面进行有限元计算。结果与结论:(1)有限元分析结果显示,在脊柱前屈工况下,6个固定节段中除S1节段外,其他5个固定节段模型1的螺钉应力均要高于模型2,钛棒和接骨面应力亦是如此;(2)在脊柱后伸工况中,由于截骨角度过大导致患者重心后移,使两者应力差异更加明显,其中差距最大的为L4节段螺钉,模型1明显高于模型2,差异为149.69 MPa;(3)截骨面的应力图显示,应力主要集中于截骨面的后方,而前方的应力普遍在12 MPa以下;(4)提示基于骨盆矢状位参数设计个性化截骨方案恢复强直性脊柱后凸矢状面平衡是合理、科学的,可在保证矫形效果的同时降低应力分布。

BACKGROUND:As kyphosis is mainly manifested as sagittal deformity.The angle of osteotomy is one of the key problems to be solved before operation.Insufficient and excessive correction of angle may cause secondary imbalance of sagittal spine.OBJECTIVE:To establish a three-dimensional finite element model of kyphotomy for ankylosing spondylitis by using computer-aided software,design a personalized surgical scheme based on pelvic sagittal parameters,restore sagittal balance,and analyze biomechanical characteristics.METHODS:CT data from C1 to sacrococcyx of a hospitalized patient from the Sixth Affiliated Hospital of Xinjiang Medical University were collected.According to 301 classification,kyphosis was determined as IIIA type.CT data were imported into computer modeling software to establish a three-dimensional finite element model of ankylosing spondylitis kyphosis.The values of pelvic incidence and pelvic tilt were measured,and the angle of theoretical pelvic tilt was calculated by pelvic incidence.Two different osteotomy models were designed.In model 2,the pre-osteotomy angle of L3 measured by hilar hip axis measurement was 32.2°.In model 1,and the osteotomy angle was set at 40°under the sagittal plane balance without reconstruction.The cancellous osteotomy was simulated on the two models;and the finite element calculation was carried out on the nail rod system and osteotomy surface of the model after osteotomy.RESULTS AND CONCLUSION:(1)Finite element analysis results showed that in the condition of spinal flexion,except S1 segment,the screw stress of model 1 of the other five fixed segments was higher than that of model 2,and the stress of titanium rod and bone connecting surface was also the same.(2)In the condition of spinal extension,due to too large osteotomy angle,the patient’s center of gravity moved backward,resulting in more obvious stress difference between the two.The largest distance was L4 segment screw,and the difference was 149.69 MPa between model 1 and model 2.(3)The stress diagram of osteotomy surface showed that the stress mainly concentrated in the rear of the osteotomy surface,while the stress in the front was generally less than 12 MPa.(4)It is a reasonable and scientific surgical plan to restore sagittal balance of ankylosing kyphosis based on pelvic sagittal parameters,which can ensure the orthopedic effect and reduce the stress distribution.