Department of Clinical Neurophysiology, Hospital Ramón y Cajal, Madrid 28034, Spain.
Spine J. 2012 Feb;12(2):127-32. doi: 10.1016/j.spinee.2011.09.006. Epub 2011 Oct 12.
Present studies concerning the safety and reliability of neurophysiological monitoring during thoracic pedicle screw placement remain inconclusive, and therefore, universally validated threshold levels that confirm osseous breakage of the instrumented pedicles have not been properly established.
The objective of this work was to analyze whether electromyographic (EMG) thresholds, after stimulation of the thoracic pedicle screw, depend on the distance between the neural structures and the screws. The modifier effect of different interposed tissues between a breached pedicle and neural structures was also investigated.
This experimental study uses a domestic pig model.
Electromyographic thresholds were recorded after the stimulation of 18 thoracic pedicle screws that had been inserted into five experimental animals using varying distances between each screw and the spinal cord (8 and 2 mm). Electromyographic thresholds were also registered after the medial pedicle cortex was broken and after different biological tissues were interposed (blood, muscle, fat, and bone) between the screw and the spinal cord.
Mean EMG thresholds increased to 14.1±5.5 mA for screws with pedicle cortex integrity that were placed 8 mm away from the dural sac. After the medial pedicle cortex was broken and without varying the distance of the screw to the dural sac, the mean EMG thresholds were not appreciably changed (13.6±6.3 mA). After repositioning the screw at a distance of 2 mm from the spinal cord and after medial cortical breach of the pedicle, the mean threshold significantly slowed to 7.4±3.4 mA (p<.001). When the screw was placed in contact with the spinal dural sac, even lower EMG thresholds were registered (4.9±1.9, p<.001). Medial pedicle cortex rupture and the interposition of different biological tissues in experimental animals did not alter the stimulation thresholds of the thoracic pedicle screws.
In the experimental animals, the observed electrical impedance depended on the distance of screws from the neural structures and not on the integrity of the pedicle cortex. The screw-triggered EMG technique did not reliably discriminate the presence or absence of bone integrity after pedicle screw placement. The response intensity was not related to the type of interposed tissue.
目前有关胸椎椎弓根螺钉置入过程中神经生理监测的安全性和可靠性的研究仍未有定论，因此，尚未确立经过验证的可确认椎弓根螺钉置入后发生骨断裂的阈值。
本研究旨在分析胸腰椎弓根螺钉刺激后肌电图（EMG）阈值是否与神经结构和螺钉之间的距离有关。还研究了椎弓根破裂与神经结构之间不同介入组织的修饰效应。
本实验研究使用国产猪模型。
使用 18 枚胸椎椎弓根螺钉刺激 5 只实验动物，记录每枚螺钉与脊髓之间的距离（8mm 和 2mm）变化时的肌电图阈值。还记录了内侧椎弓根皮质破裂后，以及在螺钉和脊髓之间介入不同生物组织（血液、肌肉、脂肪和骨骼）时的肌电图阈值。
对于距离硬脊膜囊 8mm 处的具有完整椎弓根皮质的螺钉，平均 EMG 阈值增加至 14.1±5.5mA。在不改变螺钉与硬脊膜囊之间距离的情况下，内侧椎弓根皮质破裂后，平均 EMG 阈值没有明显变化（13.6±6.3mA）。当螺钉与脊髓的距离重新定位为 2mm 且椎弓根内侧皮质破裂时，平均阈值明显降至 7.4±3.4mA（p<.001）。当螺钉接触脊髓硬脊膜时，记录到的肌电图阈值更低（4.9±1.9mA，p<.001）。在实验动物中，内侧椎弓根皮质破裂和不同生物组织的介入并未改变胸椎椎弓根螺钉的刺激阈值。
在实验动物中，观察到的电阻抗取决于螺钉与神经结构的距离，而不取决于椎弓根皮质的完整性。螺钉触发的肌电图技术不能可靠地区分椎弓根螺钉置入后骨完整性的存在与否。响应强度与介入组织的类型无关。
