Ability of electromyographic monitoring to determine the presence of malpositioned pedicle screws in the lumbosacral spine: analysis of 2450 consecutively placed screws

Clinical article

Restricted access

Object

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.

Methods

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).

Results

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.

Conclusions

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.

Abbreviation used in this paper: EMG = electromyographic.

Article Information

Address correspondence to: Timothy F. Witham, M.D., The Johns Hopkins Hospital, 600 North Wolfe Street, Meyer 7-109, Baltimore, Maryland 21287. email: twitham2@jhmi.edu.

Please include this information when citing this paper: published online April 29, 2011; DOI: 10.3171/2011.3.SPINE101.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Pedicle screw with positive EMG stimulation that was subsequently confirmed to be malpositioned on postoperative CT scan. A: The right pedicle screw represents a typical medially malpositioned screw that elicited a positive response on EMG. B: The right pedicle screw has been properly repositioned.

References

  • 1

    Belmont PJ JrKlemme WRDhawan APolly DW Jr: In vivo accuracy of thoracic pedicle screws. Spine (Phila Pa 1976) 26:234023462001

    • Search Google Scholar
    • Export Citation
  • 2

    Boucher HH: A method of spinal fusion. J Bone Joint Surg Br 41-B:2482591959

  • 3

    Calancie BLebwohl NMadsen PKlose KJ: Intraoperative evoked EMG monitoring in an animal model. A new technique for evaluating pedicle screw placement. Spine (Phila Pa 1976) 17:122912351992

    • Search Google Scholar
    • Export Citation
  • 4

    Choi WWGreen BALevi AD: Computer-assisted fluoroscopic targeting system for pedicle screw insertion. Neurosurgery 47:8728782000

    • Search Google Scholar
    • Export Citation
  • 5

    Frank EH: The use of small malleable endoscopes to assess pedicle screw placement: technical note. Minim Invasive Neurosurg 41:10121998

    • Search Google Scholar
    • Export Citation
  • 6

    Fu TSChen LHWong CBLai PLTsai TTNiu CC: Computer-assisted fluoroscopic navigation of pedicle screw insertion: an in vivo feasibility study. Acta Orthop Scand 75:7307352004

    • Search Google Scholar
    • Export Citation
  • 7

    Glassman SDDimar JRPuno RMJohnson JRShields CBLinden RD: A prospective analysis of intraoperative electromyographic monitoring of pedicle screw placement with computed tomographic scan confirmation. Spine (Phila Pa 1976) 20:137513791995

    • Search Google Scholar
    • Export Citation
  • 8

    Holland NR: Intraoperative electromyography during thoracolumbar spinal surgery. Spine (Phila Pa 1976) 23:191519221998

  • 9

    Karapinar LErel NOzturk HAltay TKaya A: Pedicle screw placement with a free hand technique in thoracolumbar spine: is it safe?. J Spinal Disord Tech 21:63672008

    • Search Google Scholar
    • Export Citation
  • 10

    Kim YJLenke LGBridwell KHCho YSRiew KD: Free hand pedicle screw placement in the thoracic spine: is it safe?. Spine (Phila Pa 1976) 29:3333422004

    • Search Google Scholar
    • Export Citation
  • 11

    Kotil KBilge T: Accuracy of pedicle and mass screw placement in the spine without using fluoroscopy: a prospective clinical study. Spine J 8:5915962008

    • Search Google Scholar
    • Export Citation
  • 12

    Lenke LGPadberg AMRusso MHBridwell KHGelb DE: Triggered electromyographic threshold for accuracy of pedicle screw placement. An animal model and clinical correlation. Spine (Phila Pa 1976) 20:158515911995

    • Search Google Scholar
    • Export Citation
  • 13

    Maguire JWallace SMadiga RLeppanen RDraper V: Evaluation of intrapedicular screw position using intraoperative evoked electromyography. Spine (Phila Pa 1976) 20:106810741995

    • Search Google Scholar
    • Export Citation
  • 14

    Raynor BLLenke LGBridwell KHTaylor BAPadberg AM: Correlation between low triggered electromyographic thresholds and lumbar pedicle screw malposition: analysis of 4857 screws. Spine (Phila Pa 1976) 32:267326782007

    • Search Google Scholar
    • Export Citation
  • 15

    Roy-Camille RSaillant GBerteaux DSalgado V: Osteosynthesis of thoraco-lumbar spine fractures with metal plates screwed through the vertebral pedicles. Reconstr Surg Traumatol 15:2161976

    • Search Google Scholar
    • Export Citation
  • 16

    Schulze CJMunzinger EWeber U: Clinical relevance of accuracy of pedicle screw placement. A computed tomographic-supported analysis. Spine (Phila Pa 1976) 23:221522211998

    • Search Google Scholar
    • Export Citation
  • 17

    Xu REbraheim NAOu YYeasting RA: Anatomic considerations of pedicle screw placement in the thoracic spine. Roy-Camille technique versus open-lamina technique. Spine (Phila Pa 1976) 23:106510681998

    • Search Google Scholar
    • Export Citation
  • 18

    Youkilis ASQuint DJMcGillicuddy JEPapadopoulos SM: Stereotactic navigation for placement of pedicle screws in the thoracic spine. Neurosurgery 48:7717792001

    • Search Google Scholar
    • Export Citation

Metrics

Metrics

All Time Past Year Past 30 Days
Abstract Views 269 269 26
Full Text Views 165 165 2
PDF Downloads 104 104 1
EPUB Downloads 0 0 0

PubMed

Google Scholar