保留椎弓根下壁截骨术在治疗陈旧性胸腰椎骨折后凸畸形力学性能的三维有限元分析

Three-dimensional finite element analysis of mechanical properties of modified partial pedicle subtraction osteotomy in treatment of post-traumatic thoracolumbar kyphosis

目的采用三维有限元分析法建立胸腰椎模型,比较保留椎弓根下壁截骨术及SRS-Schwab四级截骨术在前屈、后伸、旋转及侧弯时钉棒系统和椎体前缘内植物的应力及整体脊柱力的传导和分布。方法利用CT数据建立正常男性脊柱T11~L3模型,以L1为拟手术椎体,建立SRS-Schwab四级截骨术式(A术式)、保留1/3椎弓根下壁截骨术式(B1术式)、保留1/2椎弓根下壁截骨术式(B2术式)三维有限元模型,采用钛笼支撑椎体前缘。比较A、B1、B2术式三维有限元模型在前屈、后伸、旋转、侧弯时的总应力、各椎间隙的活动度、各内植物的应力情况,以及钛笼植入区域、剩余椎体部分、椎体剩余附属结构及钉棒系统3个部分分别的应力情况。结果在前屈、后伸、旋转和侧弯时,B2术式的总应力最小(205.6 MPa),其次为B1术式(207.0 MPa),A术式最大(217.0 MPa)。3种术式间各椎间隙活动度情况相似。内植物应力分析结果显示,B2术式在前屈、后伸、旋转及侧弯活动时,前路钛笼植入区域和后路椎体剩余附属结构及钉棒系统的应力均最小,分别为22.2、187.7、105.8、141.6和75.4、168.4、75.9、214.8 MPa;A术式均最大,分别为27.3、241.8、133.4、188.0和97.5、216.4、98.5、243.0 MPa,均远小于钛合金的屈服应力和拉伸极限(分别为760、860 MPa)。结论保留椎弓根下壁截骨术式(保留1/2椎弓根下壁)在减少手术节段应力方面具有优势,尤其是其可以减少内植物的应力,从而降低断钉断棒风险,但在保留椎间隙活动度方面与SRS-Schwab四级截骨术式相似。

Objective To establish a thoracolumbar model by three-dimensional finite element analysis,and to compare the stress conduction and distribution of screw-rod system and anterior edge of vertebral body in flexion,extension,rotation and lateral bending between modified partial pedicle subtraction osteotomy and SRS-Schwab four-stage osteotomy.Methods A T11-L3 model of normal male spine was established using computed tomography(CT)data.L1 was used as the operative vertebral body,and the three-dimensional finite element models were established for SRS-Schwab four-stage osteotomy(A operation),modified partial pedicle subtraction osteotomy with preservation of 1/3 inferior wall of pedicle(B1 operation)and modified partial pedicle subtraction osteotomy with preservation of 1/2 inferior wall of pedicle(B2 operation).Titanium mesh cage was used to support the anterior edge of vertebral body.The total stresses,the range of motion of each intervertebral space and the stress of each implant in flexion,extension,rotation and lateral bending were compared between the three-dimensional finite element models of A,B1 and B2 operations.The stresses of titanium cage implantation part,residual vertebral body,and residual accessory structure of vertebral body and screw-rod system were compared.Results During flexion,extension,rotation and lateral bending,the total stress of B2 operation was the lowest(205.6 MPa),followed by B1 operation(207.0 MPa),and that of A operation was the highest(217.0 MPa).The range of motion of each intervertebral space was similar among the three surgical methods.During flexion,extension,rotation and lateral bending,the stresses of the anterior titanium cage implantation part and remaining accessory structure and screw-rod system of posterior vertebral body of B2 operation were the lowest(22.2,187.7,105.8 and 141.6,and 75.4,168.4,75.9 and 214.8 MPa,respectively),and the stresses of A operation were the highest(27.3,241.8,133.4 and 188.0,and 97.5,216.4,98.5 and 243.0 MPa,respectively).And they were lower than yield stress and tensile limit of titanium alloy(760 and 860 MPa,respectively).Conclusion The modified partial pedicle subtraction osteotomy with preservation of 1/2 inferior wall of pedicle(B2 operation)has advantage in reducing the stress of surgical segment,especially in reducing the stress of implant,so as to decrease the risk of breaking nail and rod.However,it is similar to SRS-Schwab four-stage osteotomy in preserving the range of motion of intervertebral space.