Institute of Biomechanics, Trauma Center Murnau, Germany.
Arch Orthop Trauma Surg. 2011 Sep;131(9):1253-9. doi: 10.1007/s00402-011-1284-7. Epub 2011 Feb 26.
Compression fractures at the thoracolumbar junction are frequently treated by reconstruction with vertebral body replacement systems. Modern cage implants have been developed which respect the anatomy and angulation of the adjacent bony endplates. The objective of this study was to investigate the biomechanical performance of anatomic endplate design and variable endplate angulation.
Three cage systems [Hydrolift (HYL), Aesculap; Synex II (SYN), Synthes; Obelisc (OBC), Ulrich] were compared employing a composite bone substitute material at two levels of endplate angulation (0°, 3°). Their load-bearing capacity was assessed in a physiologic test with human vertebral specimens in a misalignment situation (3°). The HYL and SYN offered anatomically shaped endplates. The endplates of the HYL had variable angulation during insertion and were then mechanically fixated. The OBC had fixed and circular endplates. The load to failure and system stiffness were evaluated by an axial compression test. The bone mineral density (BMD) and the area of the bony endplates were measured via CT.
None of the mechanical properties differed between 0° and 3° for the HYL cage using bone substitute material, while the OBC lost 19% of the failure load (p = 0.001) and 55% of stiffness (p = 0.001) in case of misalignment. In human bone specimens, failure loads were comparable among all implants (p > 0.1) with the HYL showing the largest system stiffness (p < 0.05). Furthermore, a strong correlation between stiffness and BMD (R(2) = 0.82) and failure load and BMD (R(2) = 0.87) was found.
Anatomically shaped and continuously variable endplates provide mechanical advantages under imperfect alignment and may thus reduce secondary dislocation and the loss of correction. This is achieved by retaining an optimal contact area between the implant and the bony endplates. Conventional cage design with circular endplates offer adequate stability in optimal contact situations.
胸腰椎交界处的压缩性骨折常通过椎体置换系统进行重建治疗。目前已经开发出了一些符合解剖学结构并尊重邻近骨终板角度的新型 cage 植入物。本研究的目的是研究解剖学终板设计和可变终板角度的生物力学性能。
使用两种骨替代材料在两种终板角度（0°和 3°）下对三种 cage 系统[Hydrolift（HYL），Aesculap；Sinex II（SYN），Synthes；Obelisc（OBC），Ulrich]进行了比较。在 3°的错位情况下，用人的椎体标本在生理测试中评估它们的承载能力。HYL 和 SYN 提供了解剖形状的终板。HYL 的终板在插入过程中具有可变角度，然后通过机械固定。OBC 具有固定的圆形终板。通过轴向压缩试验评估失效负载和系统刚度。通过 CT 测量骨矿物质密度（BMD）和骨终板的面积。
在使用骨替代材料的情况下，HYL cage 的机械性能在 0°和 3°之间没有差异，而 OBC 在错位的情况下失效负载损失了 19%（p = 0.001），刚度损失了 55%（p = 0.001）。在人体骨标本中，所有植入物的失效负载无差异（p > 0.1），其中 HYL 的系统刚度最大（p < 0.05）。此外，还发现刚度与 BMD 之间存在很强的相关性（R² = 0.82），失效负载与 BMD 之间也存在很强的相关性（R² = 0.87）。
解剖形状和连续可变的终板在不完美对齐的情况下提供了机械优势，从而减少了二次脱位和矫正丢失。这是通过保持植入物与骨终板之间的最佳接触面积来实现的。具有圆形终板的传统 cage 设计在最佳接触情况下提供了足够的稳定性。
