This case report describes a patient who experienced an acute loss of both cortical and subcortical posterior tibial nerve somatosensory evoked potentials during a lumbar laminectomy procedure. The evoked potentials were lost at 10:43 during the laminectomy but recovered fully 40 minutes later at 11:23 after decompression was complete. While monitoring lower extremity SSEPs during lumbar spine surgery is controversial due to multiple nerve roots contributing to the signals, this case demonstrates that significant neural compression can be detected using SSEPs during these types of procedures.

1. Loss of Lower Extremity Somatosensory
Evoked Potentials During Lumbar
Laminectomy and Instrumented Fusion:
A Case ReportGerald A. McNamee,
R.EPT, CNIM, FACSNM

2. LOSS OF LOWER EXTREMITY SSEP DURING LUMBAR LAMINECTOMY
ABSTRACT
The utilization of lower extremity somatosensory evoked potentials (SSEP) for
monitoring of lumbar surgical procedures remains controversial in the surgical neurophysiology
community. The fact that multiple lumbar spinal nerve roots contribute to the SSEP prior to its
transition into the posterior columns of the spinal cord may lead to insensitivity in monitoring
these potentials. We present a case report of a patient undergoing a posterior approach, open,
lumbar laminectomy and instrumented fusion. This patient experienced an acute loss of both
cortical and subcortical posterior tibial nerve (PTN) SSEPs during lumbar laminectomy. Post-decompression
testing revealed a full amplitude recovery of the attenuated evoked potentials
forty minutes after loss of signal. An analysis of the case, literature review, and discussion on
the merits of SSEP monitoring in these below-the-conus medularis procedures, is presented.
Keywords: SSEP, Somatosensory Evoked Potential, Lumbar Spine Surgery, Surgical
Neurophysiology, IONM

3. LOSS OF LOWER EXTREMITY SSEP DURING LUMBAR LAMINECTOMY
CASE PRESENTATION
A 55 year old male with a past medical history of two level lumbar laminectomy and
lumbar stenosis presented for a L3/4 decompression and fusion with a revision lamino-foraminotomies
at the left L4/5 and bilateral L5/S1. The patient complained of unprovoked,
progressive, low back pain with radiation to bilateral lower extremities. The back pain is
described as aching and stabbing in nature. The patient has difficulty standing any significant
time or walking any significant distance. The patient presented conscious and fully oriented in
no acute distress. There were no gross trophic changes noted. Sensation was grossly intact to
bilateral lower extremity light touch. Strength testing revealed 5/5 (full strength) to bedside
examination from the (a) quadriceps, (b) tibialis anterior, (c) gastrocnemius, and (d) extensor
hallucis longus, bilaterally. There was no significant ankle clonus to acute dorsiflexion of either
foot.
Plain radiographs demonstrate a grade 1 spondylolisthesis at L3/4. Magnetic resonance
imaging (MRI) revealed L3/4 spinal stenosis, left L3/4 and bilateral L5/S1 intervertebral
foraminal narrowing. The conus medularis was noted at the L1 vertebral body level. The patient
had no other significant medical history or allergies to food/medicine. Preoperative screening
blood chemistry and lab results were unremarkable.
The anesthesia regimen for this case included volatile anesthetics, narcotics,
benzodiazepines, and neuromuscular blocking agents only to facilitate orotracheal intubation and
surgical exposure. The surgical neurophysiology montage included bilateral ulnar and posterior
tibial nerve SSEP and spontaneous electromyography (spEMG). EMG was collected from the
Vastus Lateralis, tibialis anterior and abductor hallucis which reflected innervation from the
L2-S1 spinal nerve roots, bilaterally. A Jackson frame was utilized for the procedure.

4. LOSS OF LOWER EXTREMITY SSEP DURING LUMBAR LAMINECTOMY
Post-prone positioning baselines showed symmetrical and monitorable waveform latencies and
amplitudes with clearly defined and consistent cortical and subcortical depolarization waveform
morphologies.
At 1015 a 3rd recording was run and all remained stable

5. LOSS OF LOWER EXTREMITY SSEP DURING LUMBAR LAMINECTOMY
At 1031 there is a slight shift in the p37 latencies of the PTSSEPs.
1031 LT Post Tibial SSEP Shift in the p37 with stable PF

6. LOSS OF LOWER EXTREMITY SSEP DURING LUMBAR LAMINECTOMY
At 1043 there is a loss of the Cortical PTSSEPs
1043 Loss of Left PTSSEP

7. LOSS OF LOWER EXTREMITY SSEP DURING LUMBAR LAMINECTOMY
At 1046 the loss was confirmed and surgeon notified.
At 1119 there continues to be a loss of the cortical PTSSEPs with preservation of
the PF potential.

8. LOSS OF LOWER EXTREMITY SSEP DURING LUMBAR LAMINECTOMY
At 1123 surgeon tells tech decompression is done and PTSSEPs return bilaterally.
At 1202 Cortical PTSSEPs remained stable.

9. LOSS OF LOWER EXTREMITY SSEP DURING LUMBAR LAMINECTOMY
At 1221 they started closing and a last trace was run with everything stable.