Limitations and pitfalls of the pedicle screw testing monitoring technique: An in vivo and in vitro study

A New Coupling Method for Accurate Measurement of Pedicle Screw Electrical Properties for Surgical Procedures

“…However, the gripping force exerted will vary according to the screw's diameter, and the teeth may not conform to the thread's shape, resulting in reduced contact surfaces and hence higher electrical resistance. The intrinsic instability of this coupling was also noted by Zyss, Bernat, Wolff, Riouallon and Pascal-Moussellard [18], who reported that rotating the screw under the clips or increasing its pressure resulted in electrical resistance changes. These assertions are corroborated by our results, with the overall increase in resistance and the higher inter-quartile range due to the reapplication of the clips or rotation of the screws, being observed in both screws specimens.…”

“…Alternatively, alligator clips are commonly reported as the chosen coupling method in this type of study [12,18,19]. The jagged shape of the clip's teeth and the bracing force provided by the spring allow an apparent good grip to the screw' threads.…”

“…The available studies have shown that electrical properties of screws can differ due to factors such as the manufacturer [16], shaft's hollowness [12] or the application of special coatings such as hydroxyapatite [17]. However, these studies used different coupling techniques to establish a contact between the pedicle screw and the measuring devices' leads, either by using unipolar probes [16], alligator clips [12,18,19] or conductive epoxy glues [16]. Since contact resistance is a well-known issue that can increase measured electrical resistance [20] and other contributing factors for increased electrical resistance can also be present in each of the above mentioned methods, the identification or development of an adequate coupling method is necessary.…”

Intraoperative Triggered Electromyography

“…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][10][11][12][13] The protocol variations in the literature point out a few potential weaknesses of this technology. We as surgeons desire tEMG to provide us binary information, when in fact, it more accurately provides graded information.…”

“…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.…”