Department of Trauma Surgery, Orthopaedic Surgery and Plastic Surgery, University Medical Center Göttingen, Robert-Koch-Str. 40, 37099, Göttingen, Germany.
Institute of Biomechanics, TUHH Hamburg University of Technology, Hamburg, Germany.
Eur Spine J. 2021 Jan;30(1):128-135. doi: 10.1007/s00586-020-06593-3. Epub 2020 Sep 17.
Inadequate anchoring of pedicle screws in vertebrae with poor bone quality is a major problem in spine surgery. The aim was to evaluate whether a modified thread in the area of the pedicle could significantly improve the pedicle screw fatigue strength.
Fourteen human cadaveric vertebral bodies (L2 and L3) were used for in vitro testing. Bone density (BMD) was determined by quantitative computed tomography. Vertebral bodies were instrumented by standard pedicle screws with a constant double thread on the right pedicle and a partial doubling of the threads-quad thread-(cortical thread) in the area of the pedicle on the left pedicle. Pulsating sinusoidal, cyclic load (0.5 Hz) with increasing peak force (100 N + 0.1 N/cycles) was applied orthogonal to the screw axis. The baseline force remained constant (50 N). Fatigue test was terminated after exceeding 5.4-mm head displacement (~ 20° screw tilting).
The mean fatigue load at failure was 264.9 N (1682 cycles) for the standard screws and was increased significantly to 324.7 N (2285 cycles) by the use of cortical threaded screws (p = 0.014). This effect is particularly evident in reduced BMD (standard thread 241.2 N vs. cortical thread 328.4 N; p = 0.016), whereas in the group of vertebrae with normal BMD no significant difference could be detected (standard thread 296.5 N vs. cortical thread 319.8 N; p = 0.463).
Compared to a conventional pedicle screw, the use of a cortical threaded pedicle screw promises superior fatigue load in vertebrae with reduced bone quality.
在骨质量差的椎骨中，椎弓根螺钉固定不牢固是脊柱外科的一个主要问题。本研究旨在评估在椎弓根区域采用改良螺纹是否能显著提高椎弓根螺钉的疲劳强度。
本研究使用 14 个人体腰椎（L2 和 L3）进行体外测试。通过定量计算机断层扫描（QCT）确定骨密度（BMD）。右侧椎弓根采用标准双螺纹椎弓根螺钉固定，左侧椎弓根的部分螺纹加倍，形成四螺纹（皮质螺纹）。对螺钉轴垂直施加脉动正弦循环载荷（0.5 Hz），逐渐增加峰值力（100 N+0.1 N/循环）。基线力保持不变（50 N）。当头部位移超过 5.4 毫米（约 20°螺钉倾斜）时，疲劳试验终止。
标准螺钉的平均失效疲劳载荷为 264.9 N（1682 个循环），而使用皮质螺纹螺钉可显著增加至 324.7 N（2285 个循环）（p=0.014）。这种效果在 BMD 降低的情况下尤为明显（标准螺纹为 241.2 N，皮质螺纹为 328.4 N；p=0.016），而在 BMD 正常的椎骨组中则未检测到显著差异（标准螺纹为 296.5 N，皮质螺纹为 319.8 N；p=0.463）。
与传统椎弓根螺钉相比，在骨质量降低的椎骨中使用皮质螺纹椎弓根螺钉可提高疲劳载荷。
