Goel V K, Kim Y E, Lim T H, Weinstein J N
Department of Biomedical Engineering, University of Iowa, Iowa City.
Spine (Phila Pa 1976). 1988 Sep;13(9):1003-11. doi: 10.1097/00007632-198809000-00007.
Three-dimensional nonlinear finite element models of the intact L4-5 one motion segment/two-vertebrae and L3-5 two motion segments/three-vertebrae were developed using computed tomography (CT) films. The finite element mesh of the L4-5 motion segment model was modified to simulate bilateral decompression surgery. The mesh was further altered to achieve stabilization, using an interbody bone graft and a set of Steffee plates and screws. The model behavior of the intact specimen in all loading modes and of the stabilized model in compression, flexion, and extension modes were studied. The stresses in the cancellous bone region were found to decrease. The interbody bone graft, due to an overall decrease in stresses in the bone below the screw, transmits about 80% of the axial load as compared with 96% transmitted by an intact disc in an intact model. Thus, the use of a fixation device induces a stress shielding effect in the vertebral body. The results indicate that although the bone graft transmits lesser loads than the intact disc, it is active in transmitting loads. The presence of low stresses in the cancellous bone region and high localized stresses in the cortical pedicle region surrounding the screw, compared with the intact case, suggests that the screws are likely to become loose over time. The use of an interbody bone graft alone or in combination with any existing fixation device also induces higher stresses at the adjacent levels. This may be responsible for the adverse iatrogenic effects seen clinically.
利用计算机断层扫描（CT）胶片建立了完整的L4-5一个运动节段/两个椎体和L3-5两个运动节段/三个椎体的三维非线性有限元模型。对L4-5运动节段模型的有限元网格进行修改，以模拟双侧减压手术。使用椎间植骨以及一组Steffee钢板和螺钉进一步改变网格以实现稳定。研究了完整标本在所有加载模式下以及稳定模型在压缩、屈曲和伸展模式下的模型行为。发现松质骨区域的应力降低。椎间植骨由于螺钉下方骨中应力的总体降低，传递了约80%的轴向载荷，而完整模型中完整椎间盘传递的轴向载荷为96%。因此，使用固定装置会在椎体中产生应力屏蔽效应。结果表明，尽管植骨传递的载荷比完整椎间盘少，但它在传递载荷方面是起作用的。与完整情况相比，松质骨区域存在低应力，而螺钉周围皮质椎弓根区域存在高局部应力，这表明随着时间的推移螺钉可能会松动。单独使用椎间植骨或与任何现有固定装置联合使用也会在相邻节段产生更高的应力。这可能是临床上所见医源性不良影响的原因。
