gms | German Medical Science

Objective: Dorsal approaches to the cervical spine are employed for a wide range of indications. With compression of the cervical spinal cord usually present in these cases, particular attention to head and neck positioning is required. The usefulness of intraoperative neuromonitoring (IONM) in gauging positioning related changes to somato-sensory evoked potentials (SSEP) and motor evoked potentials (MEP) in dorsal approaches has previously not been demonstrated in a sizable cohort.

Methods: Retrospective analysis of prospectively collected IONM data in consecutive cases of spinal canal stenosis and/or instability with signs of cervical myelopathy on T2-weighted MR imaging. SSEPs and MEPs were recorded prior to patient positioning in supine position and immediately after prone concorde positioning with the head fixed in a Mayfield head clamp. Positioning related changes in IONM data were analyzed, the incidence of patient re-positioning as well as the overall clinical outcome were assessed.

Results: 23 patients (11 male, 12 female) underwent dorsal cervical spine surgery and had both pre- and post-positioning IONM data available. Mean age was 60.7 years. Surgery was performed in 19 patients with degenerative disease (82.6%), 3 trauma cases (13%) and 1 case of neoplastic disease (4.3%). IONM was deemed reliable in 22 cases (95.7%), in one case of acute tetraplegia neither SSEPs nor MEPs could be reliably obtained. Relevant changes after prone positioning were seen in 5 cases (21.7%): all were median nerve related, with 3 patients showing an increase in median nerve SSEP latency, 1 case of median nerve SSEP amplitude loss larger 50%, and 1 patient with both increased latency and amplitude loss greater 70%. After repositioning of the cervical spine changes were fully reversible in 4 patients, partially in 1 (10% amplitude loss after re-positioning). No additional neurological deficit was encountered post-operatively.

Conclusion: 5 (21.7%) of 23 consecutively monitored patients with severe cervical spinal canal stenosis showed relevant latency increases and/or amplitude decreases from baseline median nerve SSEP immediately after concord positioning. SSEPs returned to or near baseline after re-positioning of the patient. Particularly in cases of severe stenosis and myelopathy we consider supine IONM baselines an indispensable tool to prevent further positioning-related stress on the neural structures, thus optimizing the potential for improved outcomes in this patient cohort.