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A CT-based study investigating the relationship between pedicle screw placement and stimulation threshold of compound muscle action potentials measured by intraoperative neurophysiological monitoring

Kulik, Gerit ; Pralong, Etienne ; McManus, John ; Debatisse, Damien ; Schizas, Constantin

In: European Spine Journal, 2013, vol. 22, no. 9, p. 2062-2068

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    Titel
    • A CT-based study investigating the relationship between pedicle screw placement and stimulation threshold of compound muscle action potentials measured by intraoperative neurophysiological monitoring
    Autor
    • Kulik, Gerit. Centre Hospitalier Universitaire Vaudois, The University of Lausanne, Lausanne, Switzerland
    • Pralong, Etienne. Centre Hospitalier Universitaire Vaudois, The University of Lausanne, Lausanne, Switzerland
    • McManus, John. Centre Hospitalier Universitaire Vaudois, The University of Lausanne, Lausanne, Switzerland
    • Debatisse, Damien. Centre Hospitalier Universitaire Vaudois, The University of Lausanne, Lausanne, Switzerland
    • Schizas, Constantin. Centre Hospitalier Universitaire Vaudois, The University of Lausanne, Lausanne, Switzerland
    Dokumententyp
    • Postprint
    Sprache
    • Englisch
    Veröffentlicht in
    • European Spine Journal, 2013, vol. 22, no. 9, p. 2062-2068. Springer Berlin Heidelberg
    Andere elektronische Ausgabe
    OAI-PMH-ID
    • oai:doc.rero.ch:319201
    Summary
    Purpose: Neurophysiological monitoring aims to improve the safety of pedicle screw placement, but few quantitative studies assess specificity and sensitivity. In this study, screw placement within the pedicle is measured (post-op CT scan, horizontal and vertical distance from the screw edge to the surface of the pedicle) and correlated with intraoperative neurophysiological stimulation thresholds. Methods: A single surgeon placed 68 thoracic and 136 lumbar screws in 30 consecutive patients during instrumented fusion under EMG control. The female to male ratio was 1.6 and the average age was 61.3years (SD 17.7). Radiological measurements, blinded to stimulation threshold, were done on reformatted CT reconstructions using OsiriX software. A standard deviation of the screw position of 2.8mm was determined from pilot measurements, and a 1mm of screw—pedicle edge distance was considered as a difference of interest (standardised difference of 0.35) leading to a power of the study of 75% (significance level 0.05). Results: Correct placement and stimulation thresholds above 10mA were found in 71% of screws. Twenty-two percent of screws caused cortical breach, 80% of these had stimulation thresholds above 10mA (sensitivity 20%, specificity 90%). True prediction of correct position of the screw was more frequent for lumbar than for thoracic screws. Conclusion: A screw stimulation threshold of >10mA does not indicate correct pedicle screw placement. A hypothesised gradual decrease of screw stimulation thresholds was not observed as screw placement approaches the nerve root. Aside from a robust threshold of 2mA indicating direct contact with nervous tissue, a secondary threshold appears to depend on patients' pathology and surgical conditions