H stimulus-evoked emg monitoring during transpedicular lumbosacral spine instrumentationinitial clinical results

Blair Calancie, Parley Madsen, Nathan Lebwohl

Research output: Contribution to journalArticlepeer-review

154 Scopus citations


Objectives. The authors developed and evaluated an electrophysiologic method for minimizing the risk of nerve root trauma associated with the placement of pedicle screws during transpedicular lumbosacral fixation in humans. Summary of Background Data. Various methods have been evaluated to reduce the high complication rates associated with lumbosacral transpedicular fixation, but none are without significant limitations or drawbacks. Using a pig model, we previously developed a technique for assessing, by electrophysiologic means, the potential risk associated with placement of a screw at a given site. In this report, the authors de-scribe their experience with this technique in patients. Methods. Electromyogram (EMG) was monitored from eight lower extremity muscles bilaterally. Square- wave electrical shocks (200 /usee, 7 mA) were delivered through the instruments used to form and evaluate each pedicle hole, and through the screw itself if placement was deemed safe. Provided that the instruments used (e.g., awl, tap, probe) do not exit from bone in any direction below the entry point, the resistance of bone to the 7 mA stimulus intensity is high enough such that no nerve roots are stimulated, and the EMG traces remain flat. Conversely if EMG is evoked, it warns of a potential perforation in a pedicle wall or in the anterior body. Results. The authors evaluated this technique in 18 patients in whom a total of 102 screws were placed. Based on results of electrophysiologic and palpatory evaluation, 68% of the screws were placed in a satisfactory manner. Electrophysiologic evidence of a perfora-tion, which could not be confirmed by palpation or visualization, was seen in another 13% of this total. The remaining 19% of screw placements involved sites where a defect was missed originally by palpation alone, but was located based on electrophysiological testing combined with palpation and visualization (11%), and where a perforation was initially palpated (8%). There was no postoperative morbidity associated with malpositioned screws. Conclusions. Our results indicate that the technique is sensitive and, based on early clinical results, reliable From The Miami Project to Cure Paralysis and Department of Neurological Surgery, and the Department of Orthopaedics and Reha-bilitation, University of Miami School of Medicine, Miami, Florida. Supported by the Miami Project to Cure Paralysis. Device status category: 1. 2780 Accepted for publication April 6, 1994. in the detection of perforations in pedicle screw placement. Moreover, the method is inexpensive, rapid, and easily implemented into a standard intraoperative monitoring protocol.

Original languageEnglish (US)
Pages (from-to)2780-2786
Number of pages7
Issue number24
StatePublished - Dec 1994


  • EMG
  • Intraoperative monitoring
  • Lumbar spine
  • Pedicle screws

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine
  • Clinical Neurology


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