Bosnjak R, Dolenc V V
Department of Neurosurgery, University Hospital Center, Ljubljana, Slovenia.
Spine (Phila Pa 1976). 2000 Mar 15;25(6):703-8. doi: 10.1097/00007632-200003150-00009.
A comparison of electrical thresholds for biomechanical response in the ankle and for evoked electromyographic signals from specific leg muscles during intraoperative extradural direct stimulation of roots L4, L5, and S1.
To determine whether a biomechanical response in the ankle to direct root stimulation occurs before evoked electromyographic signals and to determine differences in electrical excitability of the roots circumferentially.
Stimulus intensities of 1.2-5.7 mA are reported to evoke electromyographic response in corresponding muscles to direct stimulation of normal roots. Stimulus intensities of 6-8 mA were suggested to detect bony pedicular compromise by stimulation of a hole or a screw during pedicle instrumentation. Electrical thresholds of three-dimensional torque response in the ankle to direct root stimulation have not yet been evaluated and compared with thresholds of evoked electromyogram.
Direct monopolar stimulation of the surgically exposed roots L4, L5, and S1 was performed from different sites around the root by a cuff multielectrode. Biomechanical response was measured as an isometric torque in the ankle at each of three orthogonal axes. Compound muscle action potentials (CMAPs) from root-specific muscles were detected by a pair of surface or wire electrodes.
Mean threshold for biomechanical response in the ankle to stimulation of roots L4, L5, and S1 was 0.72 +/- 0.39 mA and for CMAP response was 1.09 mA +/- 0.36 (N = 13). Thresholds for biomechanical responses were significantly lower than for CMAP responses (P = 0.0004; paired t test). Nerve roots were electrically most excitable on their ventral aspects.
The biomechanical response in the joint to root stimulation can be used to test all root-related muscles crossing that joint at their individual innervation pattern and their residual innervation and to detect electrical excitation of the root at electric thresholds lower than those for detecting CMAP from single standard root-specific muscle. However, this method does not provide sufficient root specificity. It will be valuable in conjunction with multimodality neurophysiologic monitoring of the roots for earlier and more reliable detection of pedicle bone breakthrough or integrity. Further clinical investigations are suggested.
术中硬膜外直接刺激L4、L5和S1神经根时，比较踝关节生物力学反应的电阈值与特定腿部肌肉诱发肌电图信号的电阈值。
确定踝关节对直接神经根刺激的生物力学反应是否先于诱发肌电图信号出现，并确定神经根周向电兴奋性的差异。
据报道，1.2 - 5.7 mA的刺激强度可在直接刺激正常神经根时诱发相应肌肉的肌电图反应。有人建议，在椎弓根器械操作过程中，通过刺激钻孔或螺钉，6 - 8 mA的刺激强度可检测椎弓根骨质破坏。踝关节对直接神经根刺激的三维扭矩反应的电阈值尚未进行评估，也未与诱发肌电图的阈值进行比较。
使用袖带多电极从神经根周围不同部位对手术暴露的L4、L5和S1神经根进行单极直接刺激。生物力学反应通过在三个正交轴上测量踝关节的等长扭矩来评估。通过一对表面电极或针电极检测来自特定神经根肌肉的复合肌肉动作电位（CMAP）。
L4、L5和S1神经根刺激时，踝关节生物力学反应的平均阈值为0.72±0.39 mA，CMAP反应的平均阈值为1.09 mA±0.36（N = 13）。生物力学反应的阈值显著低于CMAP反应的阈值（P = 0.0004；配对t检验）。神经根在腹侧电兴奋性最高。
关节对神经根刺激的生物力学反应可用于以其各自的神经支配模式和残余神经支配来测试穿过该关节的所有与神经根相关的肌肉，并在低于从单个标准神经根特定肌肉检测CMAP的电阈值时检测神经根的电兴奋。然而，该方法不能提供足够的神经根特异性。与神经根的多模态神经生理监测相结合，对于更早、更可靠地检测椎弓根骨质突破或完整性将具有重要价值。建议进行进一步的临床研究。
