Electrical stimulation properties of carbon fiber versus titanium pedicle screw instrumentation: illustrative case

BACKGROUND Carbon fiber (CF) instrumentation is a useful tool for the treatment of spinal oncological disease. CF produces less instrumentation artifact on imaging, facilitating radiation planning and oncological monitoring. CF screws have different physical properties than traditional titanium, leading to decreased manual feedback during placement. Electromyography (EMG) monitoring is an intraoperative adjunct to assist in safe screw placement. While titanium and CF have different electrical properties, there is no literature comparing their responses to intraoperative stimulation. OBSERVATIONS The authors present a case of mobile spine chordoma at L1 previously stabilized at an outside hospital. During en bloc resection, asymptomatic titanium screws at L2 were replaced with CF-reinforced PEEK (CFR-PEEK) (Icotec). Stimulation of the CFR-PEEK screws at 2 mA resulted in quadriceps EMG firing. Titanium screws at L3 required 10 mA of stimulation to produce an EMG signal (DePuy Synthes). Intraoperative CT demonstrated optimal screw placement. Postoperatively, the patient was neurologically intact. In ex vivo analysis, the CFR-PEEK screw exhibited increased resistivity and decreased conductivity compared to an analogous titanium screw. LESSONS Surgeons and intraoperative monitoring teams should be aware of lower EMG stimulation thresholds for CF screws than titanium. Additional adjuncts, such as intraoperative imaging, may be helpful in these cases.