Wave changes in intraoperative transcranial motor-evoked potentials during posterior decompression and dekyphotic corrective fusion with instrumentation for thoracic ossification of the posterior longitudinal ligament.

BACKGROUND

A prospective clinical study of amplitudes of intraoperative transcranial motor-evoked potentials (TcMEPs) was performed in patients undergoing surgery for the posterior longitudinal ligament of thoracic spine (T-OPLL).

OBJECTIVE

To investigate intraoperative TcMEPs during posterior decompression and dekyphotic corrective fusion with instrumentation for T-OPLL.

METHODS

The subjects were 33 patients with an average age of 48 years at surgery who underwent posterior decompression and fusion with instrumentation under intraoperative TcMEP monitoring. Age, gender, BMI, modified McCormick scale, prone and supine position test (PST), operative time, estimated blood loss, and Japanese Orthopaedic Association (JOA) score were recorded. Rates of successful appearance of TcMEPs, factors related to successful appearance, intraoperative amplitude changes, procedures related to amplitude deterioration, recovery of amplitude, procedures related to recovery, and postoperative paralysis were also investigated.

RESULTS

The rate of appearance was highest from the abductor hallucis (AH) (83.3%) compared with other muscles. There were 24 cases with amplitude deterioration: during exposure in 6, screwing in 2, and decompression in 16. No deterioration occurred during rod placement. There were 13 (39%) with postoperative motor deficits. Significantly lower rates of amplitude appearance occurred in cases with BMI, positive PST, modified McCormick scale IV, and preoperative JOA score.

CONCLUSIONS

AH muscles were particularly useful for functional assessment of corticospinal conduction. High BMI, positive PST, modified McCormick scale IV, and low preoperative JOA score were associated with low rates of amplitude appearance. Amplitude deteriorations occurred throughout surgery, except during rod placement, and speedy rigid rod placement is important.