|
Year |
2002 |
|---|---|
|
Question Number |
31. |
|
Category |
Spine |
Question
What type of neurologic monitoring is most accurate during reduction of a grade II spondylolisthesis?
1- Electromyography
2- Electroencephalography
3- Somatosensory-evoked potentials
4- Motor-evoked potentials
5- Clonus test
Figures
Answer (click for answer)
Preferred Response: 1
Intraoperative neurological monitoring has six goals:
1. Immediate identification of acute neurologic impairment enabling prompt correction of the cause;
2. Prompt identification of acute systemic impairment, such as that due to hypoxia or hypertension;
3. The identification of nervous tissue within or around a tumor;
4. Identification of the location of a lesion within a neural pathway;
5. Application of monitoring to high risk patients to make surgical procedures available to them;
6. The reassurance provided by monitoring allows the surgeon to carry out more extensive procedures in demanding cases such as tumor resection and deformity correction.
The procedure described in this question typically involves the placement of screws into the pedicles of the segments involved in the spondylolisthesis. Two types of neurological monitoring are employed during this procedure and include: Somatosenory evoked potentials (SSEPS) and Electromyography (EMG). SSEP’s are noninvasive and use stimulation of the peripheral nerves, however, they are neither specific nor adequately sensitive to detect single root damage caused by a pedicle screw.
Screws placed into pedicles can "breakthrough" and enter the spinal canal. This complication can cause radicular pain, a dural tear, or even lacerate the nerve root. EMG has the ability to detect an incorrectly placed pedicle screw by monitoring the EMG response elicited by electrical stimulation of the motor root through screw. If the screw tip is located in the pedicle, high stimulation intensity is required to evoke a response from the muscles innervated by the nerve root. If the screw has breached the pedicle cortex and directly or indirectly touches the motor root, with or without compression, the stimulation threshold for eliciting the EMG response is significantly decreased.
Reference: Herdmann J, Deletis V, Edmonds H, Morota N: Spinal cord and Nerve root monitoring in Spine surgery and related procedures. Spine 1996;21:879-885.