Hospital Clinico Universitario de Valladolid, Calle Ramon y Cajal, 47008 Valladolid, Spain.
Ruetschi Technology SA, Fabrikstrasse 35, 3286 Muntelier, Switzerland.
Orthop Traumatol Surg Res. 2021 Nov;107(7):102918. doi: 10.1016/j.otsr.2021.102918. Epub 2021 Mar 31.
Instrumented posterior lumbar fusion with top-loading pedicle screw systems (PSS) requires fully tightened set screws to achieve a secure fixation and symmetric load condition. This assumes a complete reduction of the rod by 90°, which is not always attainable in situ, especially under constraint. The objective of this work is to compare the mechanical performance of different innovative set screw technologies, which should improve the tightening process.
The hypotheses of the study are that modifications to the screw and screwdriver unit can (1) improve the quality of set screw tightening and (2) increase the axial gripping capacity of the construct.
The four set screw technologies under investigation include a standard set screw with a flat surface (F-S; control group), a set screw with a convex surface (C-S) and a shaft tip method screwdriver used in combination with both flat (F-STM) and convex set screws (C-STM). The quality of set screw tightening is categorized as follows: failed=the rod is not completely reduced; reduced=the rod is successfully reduced but the set screw is not correctly fixed; good=remaining cases. An axial gripping capacity test is performed by a universal testing machine (Instron®) with a force capacity of 5kN.
Regarding the quality of set screw tightening, comparisons between F-S vs. F-STM, F-S vs. C-STM and between C-S vs. C-STM show statistically significant differences (p<0.001). The axial gripping capacity test shows mean gripping forces of 1223N (STD 331) in the F-STM group and of 1724N (STD 168) in the C-STM group with statistically significant differences between both groups (p=0.003).
Several biomechanical and clinical case studies have identified possible effects of misaligned rod-screw interfaces such as screw pull-out during rod reduction, screw loosening, screw or rod breakage, misalignment, adjacent segment degeneration and worsening of the clinical outcome. C-STM-technology thus supports controlled fixation in the sense of applying appropriate forces for correction or fixation during PSS assembly as well as friction-reduced final alignment and tightening with the aim to reduce implant loosening, hardware failure and reoperations, while respecting anatomical and biomechanical balance.
采用顶载椎弓根螺钉系统（PSS）进行后路腰椎融合术需要完全拧紧固定螺钉以实现牢固固定和对称的负载状态。这假设棒完全通过 90°的旋转复位，而在实际情况下，尤其是在受到约束的情况下，这并不总是能够实现的。本研究的目的是比较不同创新型固定螺钉技术的机械性能，这些技术应能改善拧紧过程。
研究的假设是，螺钉和螺丝刀组件的改进可以（1）提高固定螺钉的拧紧质量，（2）增加构建体的轴向夹持能力。
研究中调查的四种固定螺钉技术包括带有平面的标准固定螺钉（F-S；对照组）、带有凸面的固定螺钉（C-S）以及与平面（F-STM）和凸面固定螺钉（C-STM）结合使用的轴尖方法螺丝刀。固定螺钉拧紧质量分为以下几类：失败=棒未完全复位；已复位=棒已成功复位但固定螺钉未正确固定；良好=其余情况。轴向夹持能力测试使用万能试验机（Instron®）进行，力容量为 5kN。
关于固定螺钉拧紧质量，F-S 与 F-STM、F-S 与 C-STM 以及 C-S 与 C-STM 之间的比较显示出统计学上的显著差异（p<0.001）。轴向夹持能力测试显示 F-STM 组的平均夹持力为 1223N（STD 331），C-STM 组的平均夹持力为 1724N（STD 168），两组之间存在统计学显著差异（p=0.003）。
一些生物力学和临床病例研究已经确定了杆螺钉界面未对准的可能影响，例如在棒复位过程中螺钉拔出、螺钉松动、螺钉或棒断裂、未对准、相邻节段退化和临床结果恶化。因此，C-STM 技术支持在 PSS 装配过程中施加适当的力进行矫正或固定的受控固定，以及减少摩擦的最终对准和拧紧，以减少植入物松动、硬件故障和再次手术，同时尊重解剖和生物力学平衡。
