Kosmopoulos Victor, Keller Tony S, Schizas Constantin
Department of Orthopaedic Surgery, Bone and Joint Research Center, University of North Texas Health Science Center, Fort Worth, TX 76107, USA.
Eur Spine J. 2009 Jan;18(1):59-68. doi: 10.1007/s00586-008-0828-1. Epub 2008 Nov 26.
Vertebroplasty and kyphoplasty have been reported to alter the mechanical behavior of the treated and adjacent-level segments, and have been suggested to increase the risk for adjacent-level fractures. The intervertebral disc (IVD) plays an important role in the mechanical behavior of vertebral motion segments. Comparisons between normal and degenerative IVD motion segments following cement augmentation have yet to be reported. A microstructural finite element model of a degenerative IVD motion segment was constructed from micro-CT images. Microdamage within the vertebral body trabecular structure was used to simulate a slightly (I = 83.5% of intact stiffness), moderately (II = 57.8% of intact stiffness), and severely (III = 16.0% of intact stiffness) damaged motion segment. Six variable geometry single-segment cement repair strategies (models A-F) were studied at each damage level (I-III). IVD and bone stresses, and motion segment stiffness, were compared with the intact and baseline damage models (untreated), as well as, previous findings using normal IVD models with the same repair strategies. Overall, small differences were observed in motion segment stiffness and average stresses between the degenerative and normal disc repair models. We did however observe a reduction in endplate bulge and a redistribution in the microstructural tissue level stresses across both endplates and in the treated segment following early stage IVD degeneration. The cement augmentation strategy placing bone cement along the periphery of the vertebra (model E) proved to be the most advantageous in treating the degenerative IVD models by showing larger reductions in the average bone stresses (vertebral and endplate) as compared to the normal IVD models. Furthermore, only this repair strategy, and the complete cement fill strategy (model F), were able to restore the slightly damaged (I) motion segment stiffness above pre-damaged (intact) levels. Early stage IVD degeneration does not have an appreciable effect in motion segment stiffness and average stresses in the treated and adjacent-level segments following vertebroplasty and kyphoplasty. Placing bone cement in the periphery of the damaged vertebra in a degenerative IVD motion segment, minimizes load transfer, and may reduce the likelihood of adjacent-level fractures.
据报道，椎体成形术和后凸成形术会改变治疗节段及相邻节段的力学行为，并被认为会增加相邻节段骨折的风险。椎间盘（IVD）在椎体运动节段的力学行为中起重要作用。关于骨水泥强化后正常与退变的IVD运动节段之间的比较尚未见报道。从显微CT图像构建了退变IVD运动节段的微观结构有限元模型。利用椎体小梁结构内的微损伤来模拟轻度（I = 完整刚度的83.5%）、中度（II = 完整刚度的57.8%）和重度（III = 完整刚度的16.0%）损伤的运动节段。在每个损伤水平（I - III）研究了六种可变几何形状的单节段骨水泥修复策略（模型A - F）。将IVD和骨应力以及运动节段刚度与完整和基线损伤模型（未治疗）进行比较，同时也与之前使用相同修复策略的正常IVD模型的研究结果进行比较。总体而言，可以观察到退变和正常椎间盘修复模型在运动节段刚度和平均应力方面存在微小差异。然而，我们确实观察到在IVD早期退变后，终板膨出减少，并且微观结构组织水平应力在两个终板以及治疗节段中重新分布。与正常IVD模型相比，沿椎体周边放置骨水泥的骨水泥强化策略（模型E）在治疗退变IVD模型时显示出平均骨应力（椎体和终板）有更大程度的降低，被证明是最具优势的。此外，只有这种修复策略以及完全骨水泥填充策略（模型F）能够将轻度损伤（I）的运动节段刚度恢复到损伤前（完整）水平以上。IVD早期退变对椎体成形术和后凸成形术后治疗节段及相邻节段的运动节段刚度和平均应力没有明显影响。在退变IVD运动节段的受损椎体周边放置骨水泥可使负荷传递最小化，并可能降低相邻节段骨折的可能性。
