Agarwal Aakash, Agarwal Anand K, Jayaswal Arvind, Goel Vijay K
Engineering Center for Orthopaedic Research Excellence (ECORE), Department of Bioengineering and Orthopaedics Surgery, Colleges of Engineering and Medicine, University of Toledo, Toledo, 2801 W. Bancroft Toledo, OH 43606-3390, USA.
Engineering Center for Orthopaedic Research Excellence (ECORE), Department of Bioengineering and Orthopaedics Surgery, Colleges of Engineering and Medicine, University of Toledo, Toledo, 2801 W. Bancroft Toledo, OH 43606-3390, USA.
Spine Deform. 2017 Jan;5(1):18-26. doi: 10.1016/j.jspd.2016.09.047.
Analyze the effects of the distraction forces and frequencies on multiple representative scoliotic curves and to establish a relationship between high distraction forces and screw loosening.
Multiple representative finite-element models of a juvenile scoliotic spine were used to study the effects of the magnitude and frequency of distraction on growth rods.
Simulation of 6 months of growth under various distraction forces to analyze the effects of distraction forces on the biomechanics of the scoliotic spine and growth rod instrumentation; simulation of 24 months of growth under various intervals of distraction to analyze the effects of the distraction interval on the propensity for rod fracture; in vitro study to assess screw loosening after 6 months.
For all scoliotic spine model instrumented with growth rods, an optimal distraction force existed at which normal T1-S1 growth was sustained, along with minimum stresses on the rods, the lowest load at the screw-bone interface, and the least alteration in the sagittal contour. The results followed similar trends for each model, with the numerical values of optimal distraction forces in proximity for all representative scoliotic spine models. The in vitro study proved that the pullout strength of pedicle screws reduced significantly after 6 months of fatigue at higher distraction forces (in comparison with optimal distraction forces). This corroborated the finite-element findings for lower loads at the screw-bone interface with optimal distraction forces.
This study concludes that the optimal distraction forces exists for all types of scoliotic curves that have been instrumented with growth rods, which exhibits reduction of stresses on the rods with frequent distractions. This study also links the second most common complication, screw loosening, with high distraction forces. Therefore, optimizing the biomechanical environment of the dual growth rods could drastically reduce the biomechanical complications associated with growth rods.
分析撑开力和频率对多种典型脊柱侧凸曲线的影响，并建立高撑开力与螺钉松动之间的关系。
使用青少年脊柱侧凸脊柱的多个典型有限元模型，研究撑开力的大小和频率对生长棒的影响。
在不同撑开力下模拟6个月的生长，以分析撑开力对脊柱侧凸脊柱生物力学和生长棒器械的影响；在不同撑开间隔下模拟24个月的生长，以分析撑开间隔对棒断裂倾向的影响；进行体外研究以评估6个月后螺钉的松动情况。
对于所有安装了生长棒的脊柱侧凸脊柱模型，存在一个最佳撑开力，在该力下可维持T1-S1的正常生长，同时棒上的应力最小，螺钉-骨界面处的负荷最低，矢状面轮廓变化最小。每个模型的结果都呈现相似趋势，所有典型脊柱侧凸脊柱模型的最佳撑开力数值相近。体外研究证明，在较高撑开力下疲劳6个月后，椎弓根螺钉的拔出强度显著降低（与最佳撑开力相比）。这证实了有限元研究结果，即最佳撑开力下螺钉-骨界面处的负荷较低。
本研究得出结论，对于所有安装了生长棒的脊柱侧凸曲线类型，都存在最佳撑开力，频繁撑开可降低棒上的应力。本研究还将第二常见的并发症螺钉松动与高撑开力联系起来。因此，优化双生长棒的生物力学环境可大幅减少与生长棒相关的生物力学并发症。
