Prevention of spinal cord injury using brain-evoked muscle-action potential (Br(E)-MsEP) monitoring in cervical spinal screw fixation.

PURPOSE

The goal of the study was to examine waveform deterioration in intraoperative monitoring during posterior fusion with a cervical screw. This surgery is useful for alignment correction, but worsening of neurological symptoms may occur in association with screw insertion and rod installation. Therefore, spinal cord monitoring is important for safe surgery.

METHODS

The study included 25 cases treated with posterior fusion with a cervical screw. Waveform deterioration was defined as an intraoperative amplitude <50% of the control waveform. Comparisons were made between cases with normal and deteriorated waveforms.

RESULTS

Intraoperative waveform deterioration occurred in nine cases, including after screw insertion in 8 and after rod installation in one. The nine patients with deteriorated waveforms had a significantly lower preoperative JOA score (8.8 vs. 11.2, P < 0.05) and a tendency for more frequent high signal intensity on MRI [67% (6/9) vs. 31% (5/16), P = 0.087]. Cases in which stenosis was greatest at the apex of the cervical lordosis had significantly more frequent intraoperative waveform deterioration [46% (6/13) vs. 0% (0/8), P < 0.05]. In cases in which the narrowest segment was at the apex of the cervical lordosis, screw insertion before compared to after decompression significantly increased waveform deterioration [67% (6/9) vs. 0% (0/4), P < 0.05].

CONCLUSION

Intraoperative waveform deterioration in posterior cervical screw fixation is associated with severe preoperative symptoms, location of the narrowest segment, and screw insertion before decompression. It is particularly desirable to perform decompression before screw insertion in cases with the narrowest segment at the apex of the cervical lordosis.