Spine Service, Department of Orthopaedic Surgery, St George Hospital, University of New South Wales, Kogarah NSW 2217, Sydney, Australia.
Spine J. 2010 Jul;10(7):602-9. doi: 10.1016/j.spinee.2010.04.015. Epub 2010 May 23.
Discectomy is a common procedure for treating sciatica. However, both the operation and preceding herniated disc alter the biomechanical properties of the spinal segment. The disc mechanics are also altered in patients with chronic contained herniation. The biomechanical properties of the disc can potentially be restored with an elastomeric nucleus replacement implanted via minimally invasive surgery.
The purpose of this study was to determine whether the compressive characteristics of the intervertebral disc after a nucleotomy can be restored with an elastomeric nucleus replacement.
A finite element model of the L4-L5 intervertebral disc was created to investigate the effect of the implantation of an elastomeric nucleus replacement on the biomechanical properties of the disc under axial loading.
A L4-L5 physiologic intervertebral disc model was constructed and then modified to contain a range by volume of nucleotomies and nucleus replacements. The material properties of the nucleus replacement were based on experimental data for an elastomeric implant. The compressive stiffness, radial annular bulge, and stress distribution of the nucleotomy and nucleus replacement models were investigated under displacement-controlled loading.
Removal of nucleus pulposus from the physiologic disc reduced the force necessary to compress the disc 2 mm by 50%, altered the von Mises stress distribution, and reduced the outward radial annular bulge. Replacing the natural nucleus pulposus of the physiologic disc with an artificial nucleus reduced the force required to compress the disc 2 mm by 10%, indicating a restoration of disc compressive stiffness. The von Mises stress distribution and annular bulge observed in the disc with an artificial nucleus were similar to that observed in the physiologic disc.
This study demonstrates that despite having different material properties, a nucleus replacement implant can restore the axial compressive mechanical properties of a disc after a discectomy. The implant carries compressive load and transfers the load into annular hoop stress.
椎间盘切除术是治疗坐骨神经痛的常见手术。然而，手术和先前的椎间盘突出都会改变脊柱节段的生物力学特性。慢性包容型椎间盘突出症患者的椎间盘力学也会发生改变。通过微创植入弹性核替代物可以恢复椎间盘的生物力学特性。
本研究旨在确定椎间盘切除术核切除后，弹性核替代物是否可以恢复椎间盘的压缩特性。
建立了 L4-L5 椎间盘的有限元模型，以研究在轴向载荷下，弹性核替代物植入对椎间盘生物力学特性的影响。
构建了 L4-L5 生理椎间盘模型，然后对其进行修改，以包含一系列体积的核切除术和核替代物。核替代物的材料特性基于弹性植入物的实验数据。在位移控制加载下，研究了核切除术和核替代物模型的压缩刚度、径向环形膨出和应力分布。
从生理椎间盘上切除髓核会使压缩椎间盘 2mm 所需的力减少 50%，改变了 von Mises 等效应力分布，并减少了向外的环形膨出。用人工核替代生理椎间盘的天然髓核会使压缩椎间盘 2mm 所需的力减少 10%，表明椎间盘压缩刚度得到了恢复。人工核替代物椎间盘的 von Mises 等效应力分布和环形膨出与生理椎间盘相似。
本研究表明，尽管具有不同的材料特性，核替代物植入物仍可恢复椎间盘切除术后椎间盘的轴向压缩力学性能。该植入物承受压缩载荷并将载荷传递到环形环向应力中。
