Combined use of navigation (NAV) an triggered EMG for the safe placement of thoracic pedicle screws (TPS)

Abstract

[eng] Purpose The use of t-EMG potentials (t-EMGP) stimulation for TPS monitoring has been unable to establish a clear-cut value while NAV offers an alternative but at a cost of high radiation doses and prolonged surgical time. The goal was to assess if the combined use of NAV and t-EMG may decrease the radiation dose and surgical time in AIS (Adolescent Idiopathic Scoliosis) patients. Methods 329 TPS were implanted by free hand technique in 20 patients with main thoracic AIS. Whenever difficulties were found with implantation screw was skipped and placed under NAV. At the end of TPS placement was checked with screw t-EMGPs and a CT-scan was obtained of the whole instrumented spine. For those TPS with t-EMGP≤ 7 mA, the screw was removed and probed, if no breach was detected and CT determined a correct placement the screw was left in place. Results Twenty screws had a t-EMGP≤ 7 mA, the intraoperative CT-scan revealed that 11 of them were inside the pedicle, and had a normal tract feeling. The remainder 9 had a breach either medial (7) or inferior (2). The prediction chance of a t-EMGP≤ 7mA to detect a breach was higher for screws around the apex (T7-T9) (6/10 presented a breach). Additionally, 19 TPS with a threshold between 8-9mA were analysed, only 4 presented a breach either medial (3) or inferior (1). The predictive value of a t-EMGP≤ 7 mA for medial or inferior placement was only of 45%, while for t-EMGPs < 10 mA was only of 38,5%. When only TPS around the apex were analysed the positive predictive value for a t-EMGP≤ 7mA increased to 60%. Conclusion In our hands the reliability of t-EMGPs was not high enough to skip the use of CT-scan to ascertain the placement of the TPS.