Guan Yabo, Yoganandan Narayan, Maiman Dennis J, Pintar Frank A
Department of Neurosurgery, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
J Spinal Disord Tech. 2008 Jun;21(4):299-304. doi: 10.1097/BSD.0b013e31812e6276.
Determination of external and internal responses of the human lumbosacral spine using a validated 3-dimensional finite element model.
The objective of the present study was to evaluate the range of motion, disc stress, and facet joint pressure owing to anterior fusion at L4-L5 or L5-S1 level and compare with the intact spine.
A significant majority of finite element models of anterior lumbar interbody fusion are primarily focused on upper and middle levels, whereas lower spinal levels are most commonly treated with surgery.
A 3-dimensional L4-S1 finite element model, validated in the entire nonlinear range of the moment-rotation response, was used to determine ranges of motion, disc stress, and facet joint contact pressure under normal and 2 surgical conditions with bone graft and porous tantalum. Biomechanical responses were compared under flexion and extension loading between the 2 fusions and fusion masses and at the fused and intact segments.
Moment-rotation responses were nonlinear under all conditions. The range of motion at the caudal level was greater than the range of motion at the rostral level in the intact spine. The range of motion of the L4-S1 spine decreased more with the caudal than rostral fusion and more with the tantulum than bone under both loading modes. Facet joint pressures increased more with the rostral than caudal fusion. Stresses in the adjacent disc were greater with the caudal than rostral fusion under both modes of loading.
At the fused level, the caudal fusion imparted additional rigidity under flexion to the lumbosacral joint. Both fusion masses added flexibility to the adjacent segment. Under both fusion masses, increased facet joint pressure in the lumbosacral joint indicates the susceptibility of this transitional joint to long-term biomechanics-induced consequences. Increased facet joint pressures with the rostral fusion indicate that the posterior complex responds with increased load sharing, and may predispose the spine to facet-related arthropathy. Increased stresses in the adjacent disc with the caudal fusion under both modes of loading imply the potential to disc-related changes owing to long-term physiologic loading.
使用经过验证的三维有限元模型确定人体腰骶椎的外部和内部反应。
本研究的目的是评估L4-L5或L5-S1水平前路融合术后的活动范围、椎间盘应力和小关节压力，并与完整脊柱进行比较。
绝大多数腰椎前路椎间融合术的有限元模型主要集中在上段和中段，而下段脊柱是最常见的手术治疗部位。
采用一个在力矩-旋转反应的整个非线性范围内经过验证的三维L4-S1有限元模型，来确定正常和两种手术情况下（使用骨移植和多孔钽）的活动范围、椎间盘应力和小关节接触压力。比较了两种融合方式及融合块在屈伸载荷下以及融合节段和完整节段之间的生物力学反应。
在所有情况下，力矩-旋转反应均为非线性。完整脊柱中尾侧节段的活动范围大于头侧节段。在两种加载模式下，L4-S1脊柱的活动范围在尾侧融合时比头侧融合减少得更多，使用钽时比使用骨时减少得更多。小关节压力在头侧融合时比尾侧融合增加得更多。在两种加载模式下，相邻椎间盘的应力在尾侧融合时比头侧融合更大。
在融合节段，尾侧融合在屈曲时给腰骶关节增加了额外的刚度。两种融合块都增加了相邻节段的灵活性。在两种融合块情况下，腰骶关节小关节压力增加表明该过渡关节易受长期生物力学诱导后果的影响。头侧融合时小关节压力增加表明后复合体通过增加负荷分担做出反应，可能使脊柱易患与小关节相关的关节病。在两种加载模式下，尾侧融合时相邻椎间盘应力增加意味着长期生理负荷可能导致与椎间盘相关的变化。
