Polikeit Anne, Ferguson Stephen J, Nolte Lutz P, Orr Tracy E
M. E. Müller Institute for Biomechanics, University of Bern, Murtenstrasse 35, PO Box 30, 3010 Bern, Switzerland.
Eur Spine J. 2003 Aug;12(4):413-20. doi: 10.1007/s00586-002-0505-8. Epub 2002 Dec 19.
Intervertebral cages in the lumbar spine have been an advancement in spinal fusion to relieve low back pain. Even though initial stability is accepted as a requirement for fusion, there are other factors. The load transfer and its effect on the tissues adjacent to the cage may also play an essential role, which is not easily detectable with experimental tests. In this study the effects of an intervertebral cage insertion on a lumbar functional spinal unit were investigated using finite element analyses. The influences of cage material, cancellous bone density and spinal loading for the stresses in a functional spinal unit were evaluated. Three-dimensional (3D) finite element models of L2-L3 were developed for this purpose. An anterior approach for a monobloc, box-shaped cage was modelled. Models with cage were compared to the corresponding intact ones. The results showed that inserting a cage increased the maximum von Mises stress and changed the load transfer in the adjacent structures. Varying the cage material or the loading conditions had a much smaller influence than varying the cancellous bone density. The denser the cancellous bone, the more the stress was concentrated underneath the cage, while the remaining regions were unloaded. This study showed that the density of the underlying cancellous bone is a more important factor for the biomechanical behaviour of a motion segment stabilized with a cage, and its eventual clinical success, than the cage material or the applied load. Inserting an intervertebral cage markedly changed the load transfer. The altered stress distribution may trigger bone remodelling and explain damage of the underlying vertebrae.
腰椎椎间融合器是脊柱融合技术的一项进展，用于缓解下腰痛。尽管初始稳定性被认为是融合的必要条件，但还有其他因素。载荷传递及其对融合器相邻组织的影响也可能起着至关重要的作用，而这在实验测试中不易检测到。在本研究中，使用有限元分析研究了椎间融合器植入对腰椎功能脊柱单元的影响。评估了融合器材料、松质骨密度和脊柱载荷对功能脊柱单元应力的影响。为此建立了L2-L3的三维（3D）有限元模型。模拟了采用一体式盒形融合器的前路手术。将有融合器的模型与相应的完整模型进行比较。结果表明，植入融合器会增加最大von Mises应力，并改变相邻结构中的载荷传递。与改变松质骨密度相比，改变融合器材料或加载条件的影响要小得多。松质骨越致密，应力在融合器下方集中得越多，而其余区域则卸载。本研究表明，对于用融合器稳定的运动节段的生物力学行为及其最终的临床成功而言，下方松质骨的密度比融合器材料或施加的载荷更重要。植入椎间融合器显著改变了载荷传递。应力分布的改变可能会引发骨重塑，并解释下方椎体的损伤。
