J Korean Soc Spine Surg.  1998 Nov;5(2):177-183.

Evoked EMG Monitoring during Ttanspedicular Screw Fixation

• Park HJ
• Rah JH
• Hwang SK
• Lee YH

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.

MeSH Terms

Electric Stimulation
Humans
Lower Extremity
Muscles
Prospective Studies
Quadriceps Muscle
Spine