Intraoperative neuromonitoring has a poor correlation with postoperative neurological deficits in noncord level adult deformity surgery

Abstract

BACKGROUND CONTEXT: Intraoperative neuromonitoring (IONM) is routinely used during spinal deformity surgery. While it is highly effective at detecting spinal cord level changes, the utility for surgery at a noncord level is less known. The purpose of this study is to evaluate rates of new neural deficits relative to IONM alerts in noncord-level spinal deformity surgery. PURPOSE: In noncord-level spinal deformity surgery, postop neural deficits are incompletely associated with IONM alerts. The purpose of this study was to assess the efficacy of neuromonitoring in detecting and preventing neurological deficits. STUDY DESIGN/SETTING: Prospective, international, multicenter cohort. PATIENT SAMPLE: A total of 197 adult patients undergoing spinal deformity surgery at a noncord level. OUTCOME MEASURES: IONM changes defined as loss of amplitude>50% in SSEP or MEP from baseline or sustained EMG activity lasting>10 seconds were recorded. Postoperative new neurological deficits were recorded. Other outcomes measured were baseline demographics, radiographic alignment parameters, events leading to and following IONM alerts. METHODS: Twenty international centers prospectively documented IONM (EMG, SSEP and MEP), demographics, radiographic findings, and surgical events of patients (10-80 years) undergoing spinal deformity surgery. Inclusion criteria: neurologically intact, spinal deformity correction with major Cobb>80° or involving any osteotomy. IONM change was defined as loss of amplitude>50% in SSEP or MEP from baseline or sustained EMG activity lasting>10 seconds. RESULTS: Of 197 patients, 22 (11.2%) had an IONM alert. More patients were undergoing revision surgery during an alert compared to those with no alert (40.9% vs 18.9%, p = 0.026). IONM alerts did not correlate with coronal cobb angle, deformity angular ratio, sagittal vertical axis, or coronal vertical axis. There were a total of 26 alerts in 22 patients - 4 patients (18.2%) had 2 IONM alerts, while the other 18 (81.8%) had 1 alert. MEPs were affected in 21 of 26 alerts (80.8%) and 15 (71.4%) of those were recovered. Isolated MEP changes were seen in 16 of 26 alerts (61.5%). SSEPs were affected in 8 of 26 alerts (30.8%). Isolated SSEP changes were seen in 3 (11.5%). Lastly, EMGs were affected in only 2 (7.7%) and were isolated. Five of 21 MEP alerts (23.8%) were bilateral, whereas 16 (76.2%) were unilateral. The most frequent event preceding an MEP change was an osteotomy in 6 (28.6%) of 21 patients. The most frequent nonsurgical event preceding an MEP alert was technical in 5 (23.8%), followed by systemic (low blood pressure/anemia) and anesthetic in 3 patients each (14.3%). Thirty-three of 197 patients (16.8%) developed a new postop neural deficit. Of these patients, 24 (72.7%) had no IONM alert. In the presence of an IONM alert 9 of 22 (40.9%) had a new neural deficit. IONM alert and development of new neural deficit had a crude negative predictive value (NPV) of 86.1%. CONCLUSIONS: In noncord-level spinal deformity surgery, IONM alerts occurred in 11.2% of patients, with osteotomy being the most frequent preceding surgical event. A new postop neural deficit was observed in 16.8% of all patients, and in 41% of patients with a IONM alert. A surprisingly high 73% of postop neural deficits occurred in patients who did not have an alert. This highlights the need for further refinement of IONM techniques and alert criteria for noncord-level surgery. FDA Device/Drug Status: This abstract does not discuss or include any applicable devices or drugs.