• Kazuyoshi Kobayashi, Shiro Imagama, Zenya Ito, Kei Ando, Tetsuro Hida, and Naoki Ishiguro.
• Department of Orthopedic Surgery, Nagoya University Graduate School of Medicine, 65 Tsurumai Showa-ward, Aichi, Nagoya, 466-8550, Japan.
• Eur Spine J. 2017 Apr 1; 26 (4): 1154-1161.

PurposeThe 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.MethodsThe 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.ResultsIntraoperative 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].ConclusionIntraoperative 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.

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