The dreaded false negatives – when intraoperative neuromonitoring fails to detect neural deficits associated with complex, noncord-level spinal deformity corrections

BACKGROUND CONTEXT: Preservation of postoperative neural function is necessary to the success of operations to address spinal deformity. PURPOSE: To evaluate rates of new neural deficits relative to intraoperative neuromonitoring (IONM) alerts in noncord-level spinal deformity operations. STUDY DESIGN/SETTING: Prospective, international, multicenter cohort analysis. PATIENT SAMPLE: Patients meeting the following criteria: age 10-80 years and undergoing spinal deformity correction for a major Cobb>80° or involving any osteotomy at noncord level (deformity apex in the lumbar spine or an IONM change in the lumbar spine defined as loss of amplitude>50% in SSEP or MEP from baseline or sustained EMG activity lasting>10 seconds). OUTCOME MEASURES: Patient demographics, radiographic findings, IONM details, and rates of new neurological deficits. METHODS: Twenty international centers prospectively documented IONM (EMG, SSEP, MEP), demographics, radiographs, and surgical events of patients (age 10-80 years) undergoing spinal deformity correction for a major Cobb>80° or involving any osteotomy at noncord level (deformity apex in the lumbar spine or an IONM change in the lumbar spine defined as loss of amplitude>50% in SSEP or MEP from baseline or sustained EMG activity lasting>10 seconds). Neural exams were performed postop. RESULTS: In 197 noncord-level operations, there was an 16.8% incidence of new neural deficits with 24 patients (72.7%) having no IONM change. No IONM alerts occurred in 175/197 patients (88.8%). In patients with no IONM alert, 24 (13.7%) had a new neural deficit (ie, false negatives), which consisted of decrease of the ASIA LEMS score of at least 1 point from baseline in hip flexors (n=14; 58.3%), knee extensors (n=12; 50.0%), ankle dorsiflexors (n=4; 16.7%), ankle plantarflexors (n=3; 12.5%), great toe extensors (n=9; 37.5%), and/or sensory deficits (n=3; 12.5%). When MEPs of the specific muscle groups were tested, false negative rates for individual muscle groups were highest for more proximal muscle groups (hip flexion-31.8%; knee extensors-50.0%; dorsiflexion-18.2%; plantarflexors-27.3%). Overall, of the 22 false negative patients, 59.1% had at least one motor deficit when all muscle groups were tested. CONCLUSIONS: New neural deficits occurred in 13.7% of patients without having IONM alerts in this multicenter, international prospective study of noncord-level spinal deformity operations. Despite monitoring all muscle groups, 59.1% of false negative patients had at least one motor deficit. This is confirmation that development of new IONM modalities that are more sensitive to root-level neural injuries (particularly proximal muscle groups) is needed to complement the current multimodal IONM strategies for spinal deformity operations. FDA Device/Drug Status: This abstract does not discuss or include any applicable devices or drugs.

Duke Scholars

Author Christopher Ignatius Shaffrey Orthopaedic Surgery