Can intraoperative neurophysiologic monitoring during cervical spine decompression predict post-operative segmental C5 palsy?

BACKGROUND: C5 nerve root palsy is a known complication after cervical laminectomy or laminoplasty, characterized by weakness of the deltoid and bicep brachii muscles. The efficacy of intraoperative monitoring of these muscles is currently unclear. In the current prospective study, intraoperative monitoring through somatosensory (SSEPs), motor (TcMEPs) evoked potentials and real-time electromyography activity (EMG) were analyzed for their ability to detect or prevent deltoid muscle weakness after surgery. METHODS: One hundred consecutive patients undergoing laminectomy/laminoplasty with or without fusion were enrolled. Intraoperative SSEPs, TcMEPs and EMGs from each patient were studied and analyzed. RESULTS: Intraoperative EMG activity of the C5 nerve root was detected in 34 cases, 10 of which demonstrated a sustained and repetitive EMG activity lasting 5 or more minutes. Paresis of the unilateral deltoid muscle developed in 5 patients, all from the group with sustained C5 EMG activity. None of the patients with weakness of deltoid muscle after surgery demonstrated any abnormal change in TcMEP or SSEP. CONCLUSIONS: Real-time EMG recordings were sensitive to C5 nerve root irritation, whilst SSEPs and TcMEPs were not. Sustained EMG activity of the C5 nerve root during surgery is a possible warning sign of irritation or injury to the nerve.

Repetitive vs. single transcranial electrical stimulation for intraoperative monitoring of motor conduction in spine surgery.

We studied the effectiveness of single and repetitive transcranial electrical stimulation to activate motor tracts under partial neuromuscular blockade and total intravenous anesthesia. During spinal surgery, in 10 patients, the latency and amplitude of the evoked abductor pollicis brevis muscle response after cortical stimulation was calculated and compared. The number of responses evoked by the double (pair) pulse stimulation was significantly higher (p = 0.0191) than single pulse stimulation. Repetitive stimulation caused more responses than single (p = 0.0001) or double stimulation (p = 0.0253). An increase of interstimulus interval from 1-3 msec did not significantly increase the motor response with the double pulse or repetitive stimulations. Varying the number of electrical pulses per train stimulation from 3-9 did not significantly change latency (P > 0.05) or amplitude (P > 0.05) of the motor response. The findings suggest that use of repetitive stimulation of the motor cortex is an effective method to activate motor pathway during spinal surgery.

Somatosensory-evoked potential monitoring detects iliac artery occlusion during posterior spinal fusion.

STUDY DESIGN: Report of a rare case of iliac artery occlusion occurring during posterior spinal surgery. OBJECTIVE: To clarify causes of an acute occlusion of iliac vessels during posterior spinal surgery. SUMMARY OF BACKGROUND DATA: Acute embolic occlusion of the iliac artery is a medical and surgical emergency. Iatrogenic occlusion of major vessels to the lower extremities during posterior lumbar spine operation is a rare entity. METHODS: We report this complication occurring during decompression and fusion in a 55-year-old female with history of diabetes, hyperlipidemia, and multivessels vascular disease. The application of somatosensory evoked potentials during this case detected an asymmetry of cortical responses due to low blood flow to the affected limb. RESULTS: This patient underwent endovascular intervention and placement of stents to restore the flow to the limbs. CONCLUSION: It is feasible to assume that continuous and direct pressure on the inguinal region during surgery on Jackson table was the primary cause of the iliac artery occlusion, particularly in these patients with known peripheral vascular disease. Early recognition and prompt vascular intervention can prevent serious sequelae.

Correlation between transcranial motor and somatosensory-evoked potential findings in cervical myelopathy or radiculopathy during cervical spine surgery.

BACKGROUND: The correlation between electrophysiological recordings, MR images, and physical findings in cervical stenosis and cervical myelopathy are still open to debate. The goal of this study was to determine sensitivity of motor-evoked potential (MEP) and somatosensory-evoked potential (SSEP) in detecting cervical myelopathy and its correlates with the MRI findings in patients undergoing cervical spine surgeries. METHOD: Transcranial motor-evoked potentials (TcMEPs) and SSEPs were performed intraoperatively in 100 patients. The 'baseline' recordings of TcMEPs and SSEPs were correlated with patient's physical findings as well as the MR images. RESULTS: Posterior tibial and median nerves' scalp SSEP latencies were increased in myelopathic patients compared to the radiculopathy group. MEPs recorded from distal muscles such as abductor pollicis brevis and adductor hallucis (AH) muscles were more likely to be absent in myelopathic patients compared with the patients with only radiculopathy. The myelopathic patients were more likely to have no response (NR) for the lower extremity SSEP test compared with radiculopathy patients. CONCLUSION: MEP shows more sensitivity toward detecting myelopathy which is correlated well with abnormal MR images.

Monitoring of motor evoked potentials with high intensity repetitive transcranial electrical stimulation during spinal surgery.

OBJECTIVE: Clinical utility of high voltage repetitive transcranial electrical stimulation (TES) was investigated in 46 patients undergoing spine surgery. METHODS: During spinal surgery, motor evoked potentials (MEPs) were recorded from upper or lower limb muscles following high voltage repetitive TES of motor cortex under propofol and opioid/N2O anesthesia. RESULTS: The number of responses evoked by the double pulse stimulation was significantly higher than the single pulse stimulation. A similar finding was obtained when repetitive and single pulse stimulation was compared. Compound muscle action potentials (CMAPs) were recorded from upper and lower limbs in 4 patients with cervical spine myclopathy. The CMAP was absent on the affected side in 1 patient, which improved slightly after decompression. Radiculopathy was clinically present in 6 patients undergoing posterior lumbar decompression and fusion. No improvement of MEP was noted intraoperatively after spinal decompression and instrumentation. CONCLUSION: The findings suggest that intraoperative MEP monitoring is feasible method, however, its immediate prognostic value for adequacy of neuronal decompression and improvement requires further studies with larger patient population.

Activation of the external anal and urethral sphincter muscles by repetitive transcranial cortical stimulation during spine surgery.

OBJECTIVE: Clinical utility of high intensity repetitive transcranial electrical stimulation (rTES) to elicit a response in external anal and urethral sphincter muscles was investigated in 23 patients undergoing spine surgery. METHODS: During surgery, motor evoked potentials (MEPs) were recorded from external anal sphincter (EAS), external urethral sphincter (EUS), and tibialis anterior (TA) muscles following high voltage rTES under total intravenous anesthesia. RESULTS: No neurologic sequelae occurred during or after the rTES of the motor cortex. Onset latency for the EAS muscle was 20.2 +/- 3.5 msec which was not significant compared to the EUS muscle latency at 19.9 +/- 1.8 msec. The average electrical intensity to evoke EAS response was 789 +/- 78 volts compared to the 831 +/- 11 volts of the EUS muscle. Waveform latency for the TA muscle was robust in all cases while the latencies for EAS and EUS were not always clear. CONCLUSIONS: This preliminary study shows that intraoperative MEP monitoring of the external anal and urethral muscles is feasible method in particular in circumstances where bowel and bladder function are at risk of an inadvertent injury due to surgical manipulation.