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Evaluation of intrapedicular screw position using intraoperative evoked electromyography
J Maguire1, S Wallace, R Madiga
1Knoxville Orthopedic Clinic, St. Mary's Medical Center, Tennessee, USA.
Spine
|May 1, 1995
Summary
Electrically evoked electromyography accurately detects misplaced pedicle screws during spinal surgery. This method is more sensitive than radiography, improving patient safety by preventing nerve damage.
Area of Science:
- Neurosurgery
- Spinal Fusion Techniques
- Intraoperative Monitoring
Background:
- Pedicular fixation of the lumbar spine carries a risk of nerve root damage from misplaced drill bits and screws.
- Accurate placement of pedicle screws is critical for successful spinal fusion and to avoid neurological injury.
Purpose of the Study:
- To evaluate the feasibility and efficacy of using electrically evoked electromyography (EMG) for intraoperative monitoring of pedicle screw placement.
- To determine the parameters for electrical stimulation of vertebral pedicle drill bits and screws.
Main Methods:
- Electrical stimulation was applied to 95 drill bits, 144 screws, and 34 exposed nerve roots in 36 patients undergoing spinal surgery.
- Evoked electromyographic activity was recorded from lower extremity muscles during partial neuromuscular blockade.
- A constant current threshold was analyzed to correlate with misplaced hardware.
Main Results:
- A constant current threshold of 6 mA or less was associated with drill bits and screws that breached the vertebral cortex.
- Electrically evoked EMG demonstrated 93% sensitivity in detecting misplaced hardware.
- Radiography showed only 63% sensitivity in identifying misplaced pedicle screws.
Conclusions:
- Electrically evoked EMG is a highly sensitive and valuable tool for intraoperative assessment of pedicle screw placement.
- This technique serves as an effective adjunct to radiographic examination, enhancing surgical safety and accuracy.