下腰椎融合术后路单、双侧椎弓根固定的有限元比较研究

目的建立正常人L4~5节段椎间盘切除后单/双侧椎弓根螺钉固定椎间融合的有限元模型,对两者在不同运动载荷下的稳定性和应力分布进行比较研究。方法通过正常人L4~5节段CT扫描获取断层图像,然后利用mimics软件重建人体L4~5三维模型,再通过Ansys软件前处理功能建立有限元模型,并在此基础上分别建立椎间盘切除后单侧(A)、双侧(B)椎弓根螺钉固定+椎间Cage融合模型,对两组模型分别施加5 N?m的前屈、后伸、左/右屈曲和左/右旋转载荷,比较分析椎体及植入物在不同工况下的位移及应力峰值。结果各种工况下,A组在固定侧侧屈时椎体间位移及椎弓根螺钉应力峰值最大,在后伸时椎体应力峰值最大。B组在后伸时椎体间位移峰值最大,在旋转时螺钉及椎体应力峰值最大。在后伸和固定侧侧屈工况下A组椎体间位移峰值、螺钉及椎体应力峰值较B组相差最大。结论与双侧固定相比,单侧固定融合术后在固定侧侧屈及后伸工况下发生不稳及螺钉松动、断钉的潜在风险最大。单侧固定融合术后的病人在椎间骨融合前应特别减少后伸及固定侧侧屈动作,以降低风险。

Finite element analyses of unilateral and bilateral pedicle screw fixation plus interbody fusion in lumbar spine

Objective　To analyze biomechanical characteristics of pedicle screws and lumbar under different pressure loads between unilateral and bilateral pedicle screw fixation plus interbody fusion after discectomy by creating a normal L4~5 spinal segment finite element model.　Methods　A three-dimensional finite element model was created by using CT sectional images of an intact L4~5 segment of a healthy male and then model A and model B were established. Model A was unilateral pedicle screw fixation plus interbody fusion after lumbar discectomy, and model B was bilateral pedicle screw fixation plus interbody fusion after lumbar discectomy. The lumbar variation, the changes of lumbar stress and the apex stress of pedicle screw under flexion, extension, left/right lateral bending and left/right rotation were observed in the two models.　Results　The maximum displacement and stress of pedicle screws in model A reached max under the operating models of fixed-side flexion，and the maximum stress of lumbar reached max under extension. While in model B the maximum displacement reached max under extension,and the maximum stress of screws and lumbar reached max under rotation. There was significant difference between model A and B under fixed-side flexion and extension. 　Conclusion　Compared with bilateral and unilateral fixation plus fusion, the possible potential risk of instability, screw loosening and metal breakage of unilateral fixation plus fusion was greatly increased. The movement of extension, fixed-side flexion and rotation should be reduced before bone union after unilateral fixation plus fusion.