The impact of neck extension on intraoperative neuromonitoring alerts in cervical myelopathy: A neurophysiological analysis.

OBJECTIVE

Neck extension can transiently impair spinal cord conduction in cervical myelopathy, yet posture-dependent intraoperative neurophysiological changes remain poorly characterised. We aimed to define the timing, modality involvement, reversibility, and risk factors of positioning-related intraoperative neurophysiological events during anterior cervical surgery.

METHODS

We performed a retrospective analysis of patients undergoing anterior cervical surgery for myelopathy with multimodal intraoperative neurophysiological monitoring. Posture-dependent events were defined as neurophysiological changes occurring during neck extension prior to incision. Occipitocervical extension was quantified using the occipitocervical angle on intraoperative radiographs. Preoperative MRI markers of cord vulnerability were recorded.

RESULTS

Among 117 patients, 18 neurophysiological alerts were identified, of which 12 (66%) occurred during neck extension. These events predominantly involved abrupt TcMEP amplitude reduction and were typically reversible with repositioning. Patients with posture-dependent TcMEP changes demonstrated greater occipitocervical extension and preoperative MRI markers of cord compromise, while subaxial alignment did not differ. Postoperative neurological deficits occurred only in cases with persistent, non-reversible TcMEP reduction at closure (3 events), whereas reversible changes were not followed by deficit.

CONCLUSIONS

Neck extension in cervical myelopathy can precipitate reversible, posture-dependent corticospinal conduction failure detectable by TcMEPs.

SIGNIFICANCE: These findings suggest that positioning-related neurophysiological changes reflect reduced tolerance of compressed spinal cords to mechanical stress, and highlight the importance of intraoperative positioning as a modifiable determinant of neurological risk.