• Kazuyoshi Kobayashi, Shiro Imagama, Go Yoshida, Muneharu Ando, Shigenori Kawabata, Kei Yamada, Tsukasa Kanchiku, Yasushi Fujiwara, Shinichirou Taniguchi, Hiroshi Iwasaki, Nobuaki Tadokoro, Masahito Takahashi, Kanichiro Wada, Naoya Yamamoto, Hideki Shigematsu, Masahiro Funaba, Akimasa Yasuda, Hiroki Ushirozako, Toshikazu Tani, and Yukihiro Matsuyama.
• Department of Orthopedic Surgery, Nagoya University, Nagoya, Japan.
• Spine. 2021 Feb 15; 46 (4): 268-276.

Study DesignProspective, multicenter, observational study.ObjectiveThe aim of this study was to investigate the efficacy of intervention after an alert in intraoperative neurophysiological monitoring (IONM) using transcranial motor-evoked potentials (Tc-MEPs) during surgery for thoracic ossification of the posterior longitudinal ligament (T-OPLL).Summary Of Background DataT-OPLL is commonly treated with posterior decompression and fusion with instrumentation. IONM using Tc-MEPs during surgery reduces the risk of neurological complications.MethodsThe subjects were 79 patients with a Tc-MEP alert during posterior decompression and fusion surgery for T-OPLL. Preoperative muscle strength (manual muscle testing [MMT]), waveform derivation rate at the start of surgery (baseline), intraoperative waveform changes; and postoperative motor paralysis were examined. A reduction in MMT score of ≥1 on the day after surgery was classified as worsened postoperative motor deficit. An alert was defined as a decrease in Tc-MEP waveform amplitude of ≥70% from baseline. Alerts were recorded at key times during surgery.ResultsThe patients (35 males, 44 females; age 54.6 years) had OPLL at T1-4 (n = 27, 34%), T5-8 (n = 50, 63%), and T9-12 (n = 16, 20%). The preoperative status included sensory deficit (n = 67, 85%), motor deficit (MMT ≤4) (n = 59, 75%), and nonambulatory (n = 26, 33%). At baseline, 76 cases (96%) had a detectable Tc-MEP waveform for at least one muscle, and the abductor hallucis had the highest rate of baseline waveform detection (n = 66, 84%). Tc-MEP alerts occurred during decompression (n = 47, 60%), exposure (n = 13, 16%), rodding (n = 5, 6%), pedicle screw insertion (n = 4, 5%), posture change (n = 4, 5%), dekyphosis (n = 2, 3%), and other procedures (n = 4, 5%). After intraoperative intervention, the rescue rate (no postoperative neurological deficit) was 57% (45/79), and rescue cases had a significantly better preoperative ambulatory status and a significantly higher baseline waveform derivation rate.ConclusionThese results show the efficacy of intraoperative intervention following a Tc-MEP alert for prevention of neurological deficit postoperatively.Level of Evidence: 2.Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.

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