Betz Randal R, Cunningham Bryan, Selgrath Christopher, Drewry Troy, Sherman Michael C
Shriners Hospitals for Children, Philadelphia, Pennsylvania 19140, USA.
Spine (Phila Pa 1976). 2003 Oct 15;28(20):S275-8. doi: 10.1097/01.BRS.0000092486.61943.99.
Biomechanical study.
This paper describes the biomechanical comparison of calf spines instrumented with a wedge alone versus a wedge-rod construct for the fusionless correction of scoliosis.
Current techniques for the correction of scoliosis require either anterior or posterior spinal fusion for correction. We propose a technique allowing correction via vertebral body osteotomies along with fixation using a wedge-rod construct without the requirement of intervertebral segment fusion.
Calf spines were used to test the biomechanical difference between the intact spine, transverse osteotomized spine with wedge-rod reconstruction, and transverse osteotomized spine with wedge alone reconstruction. Unconstrained segments (L1-L5) were first tested under five nondestructive static loading conditions to evaluate the intact stability of the operative motion segments in axial compression (-600 N), axial rotation (+/-5.0 Nm, 150 axial preload), flexion and extension (+/-5.0 Nm), and lateral bending (+/-5.0 Nm). Following the intact analysis, vertebral wedge osteotomies in the transverse plane were performed at the L2, L3, and L4 levels. The defects were reconstructed using the Sofamor Danek Wedge Spacer, and stainless steel TSRH one-quarter inch single rod with modified CD HORIZON 6.5-mm diameter vertebral body screws at each level (L2-L4). Standard CD HORIZON 6.5-mm bone screws and staples were used at the superior and inferior ends of the five-level construct. The wedge was on the left side and the rod and screw heads on the right side. After testing the reconstructed specimen, the TSRH rod was removed and the construct retested to evaluate the stability of the wedge alone reconstruction.
Construct stiffness was calculated as the peak applied load (N or Nm) divided by the corresponding segmental displacement (mm or degrees) normalized to the intact specimen. Reconstruction static data are expressed as a percentage change from the intact condition. Statistical analysis included descriptives, a one-way analysis of variance, and the Student-Newman-Keuls test for multiple comparisons among the reconstruction groups. Axial compression: under axial compressive loads, the stiffness of the wedge-rod construct was approximately equal to that of the intact group. The stiffness of the wedge alone construct was 56% less than that of the intact group except for extension and left lateral bending. For the other modes of loading (right rotation, left rotation, flexion, extension, right lateral bending, and left lateral bending), the wedge-rod construct was stiffer than that of the intact group. The stiffness of the wedge alone construct was consistently less than that of the intact group.
Based on the results of this biomechanical comparison, the calf spines instrumented with the wedge-rod system for fusionless correction were significantly stiffer as compared to the intact calf spine. The wedges alone were not as stiff as the intact spine. This suggests that the theory of performing transverse osteotomies of vertebral bodies with fixation with wedge-rod construct for 8 to 12 weeks, followed by removal of the rod, could provide adequate fixation and correction of a scoliotic deformity without requiring fusion of motion segments.
生物力学研究。
本文描述了单纯使用楔形装置与楔形-棒状结构装置对小牛脊柱进行非融合性脊柱侧弯矫正的生物力学比较。
目前矫正脊柱侧弯的技术需要进行前路或后路脊柱融合术来实现矫正。我们提出一种技术，通过椎体截骨术进行矫正，并使用楔形-棒状结构进行固定，无需椎间节段融合。
使用小牛脊柱来测试完整脊柱、采用楔形-棒状重建的横向截骨脊柱以及仅采用楔形重建的横向截骨脊柱之间的生物力学差异。首先在五种非破坏性静态加载条件下对无约束节段（L1-L5）进行测试，以评估手术运动节段在轴向压缩（-600N）、轴向旋转（±5.0 Nm，150轴向预载）、屈伸（±5.0 Nm）和侧屈（±5.0 Nm）时的完整稳定性。在完整分析之后，于L2、L3和L4水平进行椎体横向楔形截骨。缺损采用索法美丹尼克楔形间隔器进行重建，每个水平（L2-L4）使用不锈钢TSRH四分之一英寸单棒以及改良的CD HORIZON 6.5毫米直径椎体螺钉。在五级结构的上下端使用标准的CD HORIZON 6.5毫米骨螺钉和钉。楔形在左侧，棒和螺钉头在右侧。在测试重建标本之后，移除TSRH棒并对结构重新测试，以评估仅使用楔形重建的稳定性。
结构刚度通过施加的峰值载荷（N或Nm）除以相对于完整标本归一化后的相应节段位移（mm或度）来计算。重建静态数据表示为相对于完整状态的百分比变化。统计分析包括描述性统计、单因素方差分析以及用于重建组间多重比较的Student-Newman-Keuls检验。轴向压缩：在轴向压缩载荷下，楔形-棒状结构的刚度与完整组大致相等。除了伸展和左侧弯曲外，仅使用楔形结构的刚度比完整组低56%。对于其他加载模式（右旋转、左旋转、屈伸、右侧弯曲和左侧弯曲），楔形-棒状结构比完整组更硬。仅使用楔形结构的刚度始终低于完整组。
基于该生物力学比较的结果，与完整的小牛脊柱相比，采用楔形-棒状系统进行非融合性矫正的小牛脊柱明显更硬。仅使用楔形装置不如完整脊柱硬。这表明，对椎体进行横向截骨并使用楔形-棒状结构固定8至12周，然后移除棒的理论，可以在不需要运动节段融合的情况下提供足够的固定并矫正脊柱侧弯畸形。
