Limits and usefulness of intraoperative evoked potentials during laminoplasty

Over the past 10 years, intraoperative neurophysiological monitoring (IONM) has been widely performed during surgery for treating spondylotic cervical myelopathy. Our study considers the predictive value of IONM during laminoplasty, regarding, first, the adequacy of spinal cord decompression and, second, the long-term neuro-functional outcome.

We considered 38 patients with the diagnosis of degenerative cervical myelopathy who underwent an open-door laminoplasty. All patients were evaluated preoperatively, and at three and 12 months postoperatively, with the Japanese Orthopedic Association (JOA) point scale. Upper and lower limb somatosensory and motor evoked potentials (SSEPs and MEPs) were recorded preoperatively and intraoperatively.

During surgery, three of 38 patients showed a deterioration of SSEPs and MEPs compared to baseline values. Surgery was then converted from laminoplasty to laminectomy, resulting in the gradual restoration of the evoked potentials. The neurophysiological parameter significantly associated with a better clinical outcome was the latency of lower limbs MEPs. The 12 patients who had a more prominent reduction of the MEPs latency at the end of surgery showed a higher post-surgical JOA score, increasing ≥30% compared to baseline values at the 3- and 12-month follow-up.

Though not a predictor of clinical outcome, the IONM was essential to evaluate the effectiveness of spinal cord decompression. Reduced latency of lower limbs MEPs may predict a better clinical outcome. We suggest that IONM in patients with degenerative cervical myelopathy should be routine. It is necessary to conduct larger studies to clarify the predictive value of IONM.