Evaluation of intrapedicular screw position using intraoperative evoked electromyography.
METHODS
This study analyzed the parameters needed for electrical stimulation of vertebral pedicle drill bits and screws.


OBJECTIVE
The feasibility of using electrically evoked electromyography was studied.


BACKGROUND
Considerable potential for damage of adjacent nerve roots with incorrectly placed bits and screws exists with pedicular fixation of the lumbar spine.


METHODS
Ninety-five drill bits, one hundred forty-four screws, and thirty-four exposed nerve roots were electrically stimulated in thirty-six patients. Simultaneous evoked electromyographic activity was recorded from four muscle groups in each lower extremity during partial neuromuscular blockade.


RESULTS
A constant current threshold of 6 mA or less correlated with misplaced drill bits and screws that broached the cortex. Evoked electromyography was 93% sensitive whereas radiography was only 63% sensitive to detecting bits and screws that had broached the cortex.


CONCLUSIONS
Evoked electromyography is a valuable sensitive adjunct to radiographic examination of pedicle drill bit and screw placement.
Maguire
J
J
Knoxville Orthopedic Clinic, St. Mary's Medical Center, Tennessee, USA.
Wallace
S
S
Madiga
R
R
Leppanen
R
R
Draper
V
V
D000328:Adult; D000368:Aged; D001863:Bone Screws; D004558:Electric Stimulation; D004576:Electromyography; D005071:Evoked Potentials; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D012680:Sensitivity and Specificity; D013123:Spinal Fusion; D013126:Spinal Nerve Roots / Q000502:physiology