Fig. 3

Intraoperative neurophysiological monitoring displaying loss of tibial somatosensory evoked potentials and recovery. Loss of tibial SSEPs during intraoperative leg muscle spasms and partial recovery after decompression; the traces are in descending order of time, with the first trace in red as the baseline. The SSEP amplitudes in both tibial responses are dramatically reduced following “EMG burst activity”, as marked between the crosshairs on each trace. It is thought that the muscle spasms led to increased intradiscal pressure and then intraoperative herniation, followed by loss of tibial SSEPs. The “recovery” of SSEPs occurred following decompression of the herniated disc. The last three traces of tibial SSEPs actually look worse, possibly due to the addition of inhalational anesthesia toward the end of the operation. Full clinical recovery of function may be attributed to additional time for the patient to recover from the effects of anesthesia prior to moving her limbs. EMG electromyography, SSEP somatosensory evoked potential