Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, Florida 33136, USA.
J Neurosurg Spine. 2010 Nov;13(5):600-5. doi: 10.3171/2010.5.SPINE09536.
Percutaneous pedicle screws have recently become popularized for lumbar spinal fixation. However, successful anatomical hardware placement is highly dependent on intraoperative imaging. In traditional open surgery, stimulus-evoked electromyography (EMG) responses can be useful for detecting pedicle screw breaches. The use of insulated sleeves for percutaneous screws has allowed for EMG testing in minimally invasive surgery; however, no reports on the reliability of this testing modality have been published.
A total of 409 lumbar percutaneous pedicle screws were placed in 93 patients. Levels of instrumentation included L-1 (in 12 patients), L-2 (in 34), L-3 (in 44), L-4 (in 120), L-5 (in 142), and S-1 (in 57 patients). Intraoperative EMG stimulation thresholds were obtained using insulating sleeves over a metallic tap prior to final screw placement. Data were compared with postoperative fine-cut CT scans to assess pedicle screw placement. Data were collected prospectively and analyzed retrospectively.
There were 5 pedicle breaches (3 medial and 2 lateral; 3 Grade 1 and 2 Grade 2 breaches) visualized on postoperative CT scans (1.2%). Two of these breaches were symptomatic. In 2 instances, intraoperative thresholds were the sole basis for screw trajectory readjustment, which resulted in proper placement on postoperative imaging. Thirty-five screw trajectories were associated with a threshold of less than 12 mA. However, all breaches were associated with thresholds of greater than 12 mA. Using thresholds below 12 mA as the indicator of a screw breach, this resulted in a sensitivity of 0.0, specificity of 90.3, positive predictive value of 0.0, and negative predictive value of 0.98. Utilizing a threshold of any decreased stimulus (< 20 mA) would have detected 60% of breaches, with a mean threshold of 16.25 mA.
While these data are limited by the low number of radiographic breaches, it appears that tap stimulation with an insulating sleeve may not be reliable for detecting low-grade radiographically breached pedicles using typical stimulation thresholds (< 12 mA). Imaging-based modalities remain more reliable for assessing percutaneous pedicle screw trajectories until more robust and sensitive electrophysiological testing methods can be devised.
经皮椎弓根螺钉近来已广泛应用于腰椎固定。然而，成功的解剖学硬件放置高度依赖于术中影像学。在传统的开放性手术中，刺激诱发肌电图（EMG）反应可用于检测椎弓根螺钉破裂。对于经皮螺钉，使用绝缘套管允许进行微创外科中的 EMG 测试；然而，尚无关于这种测试方式可靠性的报告。
共在 93 名患者中放置了 409 个腰椎经皮椎弓根螺钉。器械的水平包括 L-1（12 例）、L-2（34 例）、L-3（44 例）、L-4（120 例）、L-5（142 例）和 S-1（57 例）。在最终螺钉放置之前，使用金属丝锥上的绝缘套管获得术中 EMG 刺激阈值。将数据与术后精细 CT 扫描进行比较，以评估椎弓根螺钉的放置情况。数据是前瞻性收集的，并进行回顾性分析。
术后 CT 扫描显示 5 例椎弓根破裂（3 例内侧和 2 例外侧；3 级 1 例，2 级 2 例）（1.2%）。其中 2 例破裂与症状有关。在 2 例中，术中阈值是唯一调整螺钉轨迹的基础，这导致术后影像学上的正确放置。35 个螺钉轨迹与小于 12 mA 的阈值相关。然而，所有的破裂都与大于 12 mA 的阈值相关。将低于 12 mA 的阈值作为螺钉破裂的指标，其灵敏度为 0.0，特异性为 90.3，阳性预测值为 0.0，阴性预测值为 0.98。使用低于 12 mA 的阈值（< 20 mA）将检测到 60%的破裂，平均阈值为 16.25 mA。
虽然这些数据受到放射学破裂数量较少的限制，但似乎使用绝缘套管进行丝锥刺激可能无法可靠地检测到典型刺激阈值（< 12 mA）下的低等级影像学破裂的椎弓根。在能够设计出更强大和敏感的电生理测试方法之前，基于影像学的方法仍然更可靠地用于评估经皮椎弓根螺钉轨迹。
