Reversible intraoperative neuromonitoring changes in thoracic ossification of the posterior longitudinal ligament and/or ossification of the ligamentum flavum surgery

Objective: We aim to determine the surgical outcomes in patients with thoracic ossification of the posterior longitudinal ligament (OPLL) and/or ossification of the ligamentum flavum (OLF) who experienced intraoperative somatosensory- and/or motor-evoked potential (SSEP and/or MEP) changes. Methods: Patients who diagnosed with OPLL and/or OLF were identified. SSEP/MEP signals were acquired at two time-points: (1) during the maximal signal change and (2) 20 min after the change. Manual muscle testing (MMT) and the modified Japanese Orthopedic Association Scoring System (mJOA) were obtained to assess perioperative spinal neurological function. Results: Of the 165 eligible patients, 104 experienced SSEP/MEP changes. These patients were stratified into two subgroups: 22 patients exhibited persistent signal changes, while 82 patients showed partial or complete signal recovery within 20 min after the maximum change. Patients with reversible SSEP/MEP changes had comparable surgical outcomes to those in the no-change group, including estimated blood loss (463 ±145 ml vs. 486±162 ml, p = 0.47) and operative time (205 ± 28 min vs. 213 ± 27 min, p = 0.81). Furthermore, postoperative spinal neurological function in patients with reversible change was similar to those of the no-change group in terms of short-term postoperative motor deficit (PMD) cases (reversible group: n = 4; no-change group: n = 2; p = 0.64) and long-term mJOA recovery ratio (RR) (reversible change group: 29.19% ± 9.76%; no-change group: 31.22% ± 13.91%; p = 0.21). Conclusions: Reversible signals provide surgeons with confidence to complete the surgery safely, with surgical outcomes comparable to those of patients who do not experience SSEP/MEP changes.