ABSTRACT
STUDY DESIGN: In a prospective study of 38 patients undergoing lumbar pedicle screw instrumentation 200 pedicle hole were tested intraoperatively using electrical stimulation. OBJECTIVES: To evaluate the searching stimulus intensity at pedicle in Korean and to identify the most vulnerable root in transpedicular screw fixation of lumbosacral spine. MATERIALS AND METHOD: Electromyelogram(EMG) was monitored from eight lower extremity muscles bilaterally. Constant current stimulation pulses(0.2msec duration) were delivered through a ball-tipped nasopharyngeal probe used to evaluate each pedicle hole, and evaluated for searching stimulus intensity, the current necessary to evoked EMG RESULTS: The searching stimulus intensity above 5 mA were 194 cases(97.0%), above 7mA 151cases(75.5%), above 10 mA 107 cases(53.5%) and below 5 mA were 6 cases(3.0%). The vastus medialis muscle is most sensitive in L2(100%), L3(83.3%), tibialis anterior is in L4(68.4%), peroneus longus is in L5(44.2%) and gastrocnemious is in S1(64.5%). CONCLUSIONS: Stimulus-evoked EMG monitoring is a valuable and efficacious adjunct to lumbar pedicle screw instrumentation. A stimulation threshold greater than 5 mA reliably indicates adequate screw position and the root located at infero-medial side of pedicle is most vulnerab18 in transpedicular screw fixation.