The Use of Intraoperative Neurophysiologic Monitoring During Anterior and Posterior Lumbar Interbody Fusions

Lumbar interbody fusion has become an increasingly utilized treatment for discogenic back pain and spinal instability. Concerns have been raised regarding the morbidity associated with the procedure. We reviewed 42 consecutive patients who underwent either anterior (ALIF) or posterior (PLIF) lumbar interbody fusion to address concerns of safety and usefulness of intraoperative monitoring. The most frequent indications for surgery were discogenic pain (57%), lumbar instability (23%), and instability associated with a pars interarticularis fracture (14%).

All ALIFs were performed via a transperitoneal approach except for one retroperitoneal approach. Fifty percent of PLIFs also underwent pedicle screw instrumented fusions. Continuous somatosensory evoked potentials (SSEPS) were monitored during all procedures. SSEPs were recorded in response to tibial nerve stimulation with baselines obtained after positioning and prior to skin incision. Spontaneous electromyographic (EMG) activity was also monitored during most PLIFS.

We recorded EMGs from bilateral gastrocnemius and anterior tibialis muscle groups to continuously monitor the L4 to S2 segments intraoperatively. EMG activity ranged from none (baseline) to normal motor unit discharge (reversible injury) to neurotonic injury potentials reflecting probable permanent injury with axonal loss. lntraoperatively, six patients had abnormal spontaneous EMG activity and one had reversible SSEP changes with nerve root retraction.

One patient with abnormal spontaneous EMG activity was noted to have L5 weakness postoperatively. One additional patient, who did not have EMG monitoring, was noted to have L5 weakness postoperatively.

We conclude that neurophysiologic monitoring is feasible during lumbar interbody fusion and may result in fewer neurological complications.