Retrospective Analysis of EMG-evoked Potentials in Cortical Bone Trajectory Pedicle Screws

Abstract

tEMG testing is effective for medial breaches in CBT screws. In addition, there is evidence that bicortical placement of these screws causes lower stimulation values due to distal breach. Importantly, it seems that this is due in part to stimulation of the exiting nerve root at the level above.

Intraoperative Triggered Electromyography

“…3,10,12,18 While these variations in breach rates may be multifactorial and surgeon dependent, what is consistent through all these studies is that these breaches rarely affect neurological outcomes or leads to revision surgery, with rates ranging from 0% to 0.3%. 2,4,6,10,12,17 Kotil and colleagues placed 306 screws in 54 patients in the thoracolumbar region from T10 to L5 with a free hand technique, without using intraoperative imaging or triggered EMG. The authors had a breach rate of 3.2% in the thoracolumbar spine, which was lower than the overall breach rate in the study at 5.6% for the cervical, thoracic, thoracolumbar, and sacral spine.…”

“…For comparison, other studies which do employ tEMG with or without intraoperative imaging have breach rates ranging from 1.7% to 15.6% 3,10,12,18. While these variations in breach rates may be multifactorial and surgeon dependent, what is consistent through all these studies is that these breaches rarely affect neurological outcomes or leads to revision surgery, with rates ranging from 0% to 0.3% 2,4,6,10,12,17…”

“…In addition, the low sensitivity of this technology cannot fully assure us of what we desire to be true: if the tEMG is negative, can we confidently rule out screw malposition knowing that false-negative rates range from 3% to 17%? 10,11,14 We also know that the transmission of electrical pulses can be impaired by anesthetics, variations in the impedance in the surrounding bone and blood, and the properties of the implant materials (specifically titanium alloys) used during these cases. These factors make it challenging to obtain consistently uniform and reproducible values.…”

“…From his cohort of 90 patients he concluded that intraoperative screw stimulation was extremely effective at confirming adequate screw position when confirmed by CT and that a stimulation of >15 mA provided a 98% confidence that the screw was within the pedicle. While this may appear promising, most studies that report high specificities for triggered EMG monitoring set the stimulation threshold much lower at 5–10 mA and have poor sensitivities ranging from 46% to 86% 3,9–13…”

Complications and Revisions After Spine Surgery in Patients With Skeletal Dysplasia: Have We Improved?

“…While these patients may experience progressive symptoms, surgical decision-making is a highly complex process, as spine procedures in patients with skeletal dysplasia have been associated with high rates of complications. [5][6][7][8][9] Atypical collagen leads to friable connective tissues, predisposing patients to dural tears and wound healing complications, 10 while unfamiliar anatomy may complicate the surgical approach or instrumentation, increasing the risk for neurologic injury. Furthermore, associated medical conditions place patients at high risk for cardiac or pulmonary complications, with prior case series demonstrating complication rates as high as 61% after spine surgery in patients with achondroplasia.…”