A practical method for real-time detection of pedicle wall breaching during funneling

Background: A reliable, real-time method for the detection of pedicle wall breaching during funnelling in spine deformity surgery could be accessible to any surgeon assisted with neuromonitoring. Methods: Fifty-six consecutive patients (1066 pedicles), who were submitted to spinal deformity surgery from December 2013 to July 2015 were included in the study group. A control group of 13 consecutive patients (226 pedicles) with spinal deformity surgery were operated on from January to December 2013 and were excluded from finder stimulation. In the study cohort, continuous stimulation during funnelling was delivered via a finder and subsequently a compound muscle action potential (CMAP) threshold was determined. Following funnelling, manual inspection of the pedicular internal walls was performed. The CMAP thresholds were compared with the results of palpation to determine the sensitivity and specificity of the technique for detecting pedicular breaching. To cover common ranges of damage, the medial and lateral breaches were compared and the concave-apical breaches compared to the non-apical or convex-apical breaches. In addition, a pedicle screw test was estimated for all patients. Results: ROC analysis showed 9 mA cut-off to have a sensitivity of 88.0% and a specificity of 89.5% for predicting pedicular breaching, with an area under the curve of 0.92 (95% confidence interval 0.90–0.94; P < 0.001). Using 9 mA threshold as an alert criterion, funnelling at the concave-apical pedicles showed significantly more true and false positive alerts and fewer true negative alerts when compared with the non-apical and convex-apical pedicles (P < 0.001). Medial breaches had significantly lower stimulation thresholds than lateral breaches (P < 0.001). Thresholds of screw-testing were significantly higher for study than for control-patients (P = 0.002). Conclusions: Finder stimulation has a considerably higher sensitivity and specificity for prediction of pedicular breaching, most prominent for medial breaches. Screw-testing displayed significantly better results in patients undergoing the finder stimulation technique, as compared with the control group. The main advantages of our method are its high safety level and low cost, which may be critical in less affluent countries. Level of evidence: III.