Intraoperative Neuromonitoring and posterior spinal fusion
December 07, 2020
Motor vehicle accidents can be traumatizing life-altering events that leave your body in shambles. In 2018 alone, there were over 33,000 fatal motor vehicle crashes in the US. Pair this level of devastation with pre-existing conditions and it spells a recipe for disaster. For those with an existing physical ailment such as back problems, the consequences of such an incident can be catastrophic.
A patient history consisting of lumbar radiculopathy, lumbar deformity, lumbar foraminal stenosis, conjoined L4-S1 nerve roots, and pseudoarthrosis, compounded by multiple motor vehicle accidents would seem to reflect the kinds of catastrophic consequences possible for a worst-case scenario. For one 26-year-old female patient, this was the exact set of circumstances she would be tasked with trying to navigate.
It was determined that surgical intervention would be necessary to begin correcting these pre-existing conditions. The required surgery would entail a posterior spinal fusion at L3-S2 as well as a lumbar decompression at L3-S2. This posterior spinal fusion was the insertion of a bone graft into the disc space, fusing the L3 vertebrae to the S2 vertebrae. In the process of fusing vertebrae together, it is common to remove sections of the vertebrae as in a laminectomy or portions of the damaged disc as a discectomy in order to relieve pressure on affected nerves. To prevent damage to these nerves during the fusion or discectomy, Axis intraoperative neurophysiological monitoring was used to ensure their protection.
“Two sets of eyes on the neurophysiological data help ensure that your surgeon receives real-time feedback if response time or amplitude change, allowing the surgeon to make any necessary corrections and maintain the integrity of the nerves. This allows your entire staff to have more comfort and control during the procedure,” said Dr. Faisal R. Jahangiri of AXIS Neuromonitoring in Richardson, Texas.
For this patient, both upper and lower Somatosensory Evoked Potentials (SSEP) would be used to monitor sensory stimuli including pain or touch, lower Electromyography (EMG) to monitor electrical activity of muscular tissue, Triggered Electromyography (T-EMG), and Train of Four (TOF).
When implanting screws during a spinal fusion, electrical readings should register at least 10mA or above in a normal person to demonstrate effective electrical response. While placing the left screw into the S1 vertebrae for this patient, a small cortical breach was indicated as the screw tested at 11 mA. The surgeon redirected the screw placement and re-tested. Now measuring at 8mA, and then at 7mA, the surgeon elected to remove the screw altogether. In placing the right L4 screw, a reading of at 9mA informed the surgeon to back the screw up slightly. A re-test registered this screw at 10mA. The left screw at L5 tested at 4mA, to which the surgeon adjusted the screw for a 10mA retest. In yet adjusting a third time, the L5 screw tested at 17mA. All other screws tested above 10mA.
The potential consequences of conducting this procedure without neuromonitoring are vast. If the low screw threshold was not identified by the intraoperative neuromonitoring technician, it could have resulted in severe damage to the spinal cord or the adjacent nerves. This could have resulted in paralysis. Alternatively, the patient could have experienced postoperative muscle weakness, numbness, severe pain, or foot drop, making it difficult to walk and incredibly challenging to ever climb stairs. But, because of the incorporation of Axis neuromonitoring during the surgical procedure, no neurological deficits were experienced.