Abstracts of the 2013 Annual Meeting of the AANS/CNS Section on Disorders of the Spine and Peripheral Nerves
Phoenix, Arizona • March 6–9, 2013
Scott L. Parker, Anubhav G. Amin, S. Harrison Farber, Matthew J. McGirt, Daniel M. Sciubba, Jean-Paul Wolinsky, Ali Bydon, Ziya L. Gokaslan and Timothy F. Witham
Pedicle screws provide efficient stabilization along all 3 columns of the spine, but they can be technically demanding to place, with malposition rates ranging from 5% to 10%. Intraoperative electromyographic (EMG) monitoring has the capacity to objectively identify a screw breaching the medial pedicle cortex that is in proximity to a nerve root. The purpose of this study is to describe and evaluate the authors' 7-year institutional experience with intraoperative EMG monitoring during placement of lumbar pedicle screws and to determine the clinical utility of intraoperative EMG monitoring.
The authors retrospectively studied 2450 consecutive lumbar pedicle screws placed in 418 patients from June 2002 through June 2009. All screws were inserted using a free-hand technique and anatomical landmarks, stimulated at 10.0 mA, and evaluated with CT scanning within 48 hours postoperatively. Medial pedicle screw breach was defined as having greater than 25% of the screw diameter extend outside of the pedicle, as confirmed on CT scanning or intraoperatively by a positive EMG response indicating a medial breach. The sensitivity and specificity of intraoperative EMG monitoring in detecting the presence of a medial screw breach was evaluated based on the following definitions: 1) true positive (a positive response to EMG stimulation confirmed as a breach intraoperatively or on postoperative CT scans); 2) false positive (positive response to EMG stimulation confirmed as a correctly positioned screw on postoperative CT scans); 3) true negative (no response to EMG stimulation confirmed as a correctly positioned screw on postoperative CT scans); or 4) false negative (no response to EMG stimulation but confirmed as a breach on postoperative CT scans).
One hundred fifteen pedicle screws (4.7%) showed positive stimulation during intraoperative EMG monitoring. At stimulation thresholds less than 5.0, 5.0–8.0, and > 8.0 mA, the specificity of a positive response was 99.9%, 97.9%, and 95.9%, respectively. The sensitivity of a positive response at these thresholds was only 43.4%, 69.6%, and 69.6%, respectively. At a threshold less than 5.0 mA, 91% of screws with a positive EMG response were confirmed as true medial breaches. However, at thresholds of 5.0–8.0 mA or greater than 8.0 mA, a positive EMG response was associated with 89% and 100% false positives (no breaches), respectively.
When using intraoperative EMG monitoring, a positive response at screw stimulation thresholds less than 5.0 mA was highly specific for a medial pedicle screw breach but was poorly sensitive. A positive response to stimulation thresholds greater 5.0 mA was associated with a very high rate of false positives. The authors' experience suggests that pedicle screws showing positive stimulation below 5.0 mA warrants intraoperative investigation for malpositioning while responses at higher thresholds are less reliable at accurately representing a medial breach.
Oren N. Gottfried, Scott L. Parker, Ibrahim Omeis, Ali Bydon, Ziya L. Gokaslan and Jean-Paul Wolinsky
Cervical spondylolysis is an uncommon disorder involving a cleft at the pars interarticularis. It is most often found at the C-6 level, and clinical presentations have included incidental radiographic findings, neck pain, and rarely neurological compromise. Although subaxial cervical spondylolysis has been described in 150 patients, defects at the C-2 pedicles are rare.
The authors present 2 new cases of C-2 spondylolysis in athletically active young persons who did not demonstrate instability or neurological deficits, were able to remain active, and are being managed conservatively with serial examinations and imaging. They also discuss the results of 22 previously reported cases of C-2 spondylolysis. Based on the literature and their own experience, the authors conclude that most patients with C-2 spondylolysis remain neurologically intact, maintain stability despite the bony defect, and can be managed conservatively. Surgery is reserved for patients who demonstrate severe instability or spinal cord compromise due to stenosis.