三维有限元法分析内固定类型及骨质疏松对斜外侧椎间融合的影响

Effects of internal fixation types and osteoporosis on oblique lateral interbody fusion:three-dimensional finite element analysis

背景:目前斜外侧椎间融合是否需要内固定尚有争议,骨质疏松的存在是否会对应用斜外侧椎间融合时内固定类型的选择造成影响也缺乏生物力学研究支持。目的:运用三维有限元法分析开展斜外侧椎间融合时骨质疏松及后路椎弓根钉棒的不同固定类型对腰椎生物力学的影响。方法:获取健康人L3-L5节段CT扫描数据,运用Mimics、Geomagic、Solidworks、ANSYS软件建立L3-L5正常三维有限元模型(M0)和骨质疏松模型(N0),并分别以M0、N0为基础在L4-L5节段建立斜外侧椎间融合正常腰椎单纯融合固定(stand-alone)模型(M1)、单侧椎弓根钉棒固定模型(M2)、双侧椎弓根钉棒固定模型(M3)及骨质疏松腰椎单纯融合固定模型(N1)、单侧椎弓根钉棒固定模型(N2)、双侧椎弓根钉棒固定模型(N3)。在L3上表面施加500 N垂直载荷及7.5 N·m力矩,模拟脊柱前屈、后伸、左右侧弯和左右旋转等生理活动,观察各有限元模型不同工况下L4-L5节段的相对活动度、L5上终板、融合器和钉棒系统的应力分布,并记录Von Mises应力峰值。结果与结论:(1)无论是在正常模型中还是骨质疏松模型中,随着后路内固定的增加,L4-L5活动度、L5上终板应力、融合器应力总体上均呈现下降趋势;(2)M2内固定的应力相比M3最大增大了115.26%;N2内固定的应力相比N3最大增大了78.87%;(3)同种内固定类型下,骨质疏松模型的L4-5活动度、L5上终板应力、融合器应力均较正常模型增大;(4)N2内固定的应力相比M2最大增幅为39.59%,N3内固定的应力相比M3最大增幅为43.30%;(5)提示骨密度正常、无明显序列失衡的腰椎应优先考虑单纯融合固定或单侧椎弓根钉棒固定;若腰椎存在明显序列失衡,则应联合双侧椎弓根钉棒固定;骨质疏松腰椎应联合双侧后路椎弓根钉棒进行固定,有助于降低其融合器沉降、终板塌陷的发生率,提高固定安全性。

BACKGROUND:At present,whether the oblique lateral interbody fusion requires internal fixation is still controversial,and whether the osteoporosis will affect the choice of the type of internal fixation during the application of oblique lateral interbody fusion is also lack of biomechanical research support.OBJECTIVE:To study the biomechanical effects of osteoporosis and different types of posterior pedicle screw fixation on the lumbar spine during oblique lateral interbody fusion by three-dimensional finite element method.METHODS:CT scan data of L3-L5 segments of healthy people were obtained.The normal intact three-dimensional finite element model(M0)and osteoporosis model(N0)of L3-L5 were established by using Mimics,Geomagic,Solidworks and ANSYS software.M0 and N0 were used as the basis at L4-L5 to establish the normal oblique lateral interbody fusion stand-alone model(M1),the normal oblique lateral interbody fusion with unilateral pedicle screw fixation model(M2),the normal oblique lateral interbody fusion with bilateral pedicle screw fixation model(M3),the osteoporotic oblique lateral interbody fusion stand-alone model(N1),the osteoporotic oblique lateral interbody fusion with unilateral pedicle screw fixation model(N2)and the osteoporotic oblique lateral interbody fusion with bilateral pedicle screw fixation model(N3).A vertical load of 500 N and a moment of 7.5 N·m were applied to the L3 upper surface to simulate the physiological activities of lumbar spine in flexion,extension,right/left lateral bending and right/left axial rotation.The L4-L5 segment range of motion,stress distribution of L5 superior endplate,cage,and internal fixation under different working conditions was observed.The maximum Von Mises stresses were recorded.RESULTS AND CONCLUSION:(1)Whether in the normal models or the osteoporotic models,with the increase of posterior internal fixation,the L4-L5 range of motion,the L5 superior endplate stress,and the cage stress generally showed a downward trend.(2)The internal fixation stress of M2 increased by 115.26%mostly compared with that of M3.Compared with that of N3,the internal fixation stress of N2 increased by 78.87%mostly.(3)At the same type of internal fixation,the L4-L5 range of motion,L5 superior endplate stress,and cage stress of the osteoporotic models were all higher than those of the normal models.(4)Compared with that of M2,the internal fixation stress of N2 increased by 39.59%mostly.The internal fixation stress of N3 increased by 43.30%compared with that of M3.(5)It is indicated that the lumbar spine with normal bone mineral density and without significant alignment imbalance should be given priority for oblique lateral interbody fusion stand-alone or unilateral pedicle screw fixation.If there is significant alignment imbalance in the lumbar spine,bilateral pedicle screw fixation should be combined.The lumbar spine with osteoporosis should be combined with bilateral pedicle screw fixation to help reduce the incidence of cage settlement,endplate collapse and improve surgical safety.