A prospective analysis of intraoperative electromyographic monitoring of pedicle screw placement with computed tomographic scan confirmation.
METHODS
In a prospective study of 90 patients undergoing lumbar pedicle screw instrumentation, 512 screws were tested intraoperatively using electrical stimulation. The accuracy of this technique was verified after surgery by computed tomography.


OBJECTIVE
Computed tomographic scans taken after surgery were used to evaluate the efficacy of intraoperative screw stimulation and electromyographic monitoring of pedicle screw placement.


BACKGROUND
Previous cadaveric and clinical studies showed the risk of pedicle screw malposition and the inadequate reliability of intraoperative radiographs to identify misplaced screws.


METHODS
Screws (total, 512) in 90 patients were stimulated intraoperatively, and stimulation threshold was recorded. Computed tomographic scans were taken after surgery to document pedicle screw position. Electromyographic thresholds and computed tomographic data were evaluated independently and compared to assess the accuracy of the electromyographic screw stimulation technique.


RESULTS
Intraoperative screw stimulation was extremely accurate in confirming the adequacy of screw position. A stimulation threshold greater than 15 mA provided a 98% confidence that the screw was within the pedicle. In eight of 90 patients (9%), electromyographic monitoring detected a screw malposition that was not identified on lateral radiograph.


CONCLUSIONS
Screw stimulation monitoring is a valuable and efficacious adjunct to lumbar pedicle screw instrumentation. A stimulation threshold greater than 15 mA reliably indicates adequate screw position. A stimulation threshold between 10 and 15 mA was generally associated with adequate screw position, although exploration of the pedicle is recommended. A stimulation threshold less than 10 mA was associated with a significant cortical perforation in most instances.
Glassman
S D
SD
Department of Orthopaedic Surgery, University of Louisville, Kentucky, USA.
Dimar
J R
JR
Puno
R M
RM
Johnson
J R
JR
Shields
C B
CB
Linden
R D
RD
D001863:Bone Screws; D004056:Differential Threshold; D004558:Electric Stimulation; D004576:Electromyography; D006801:Humans; D016343:Monitoring, Intraoperative; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013131:Spine / Q000601:surgery*; D014057:Tomography, X-Ray Computed