Solid and hollow pedicle screws affect the electrical resistance: A potential source of error with stimulus-evoked electromyography

Abstract

Background:Although stimulus evoked electromyography (EMG) is commonly used to confirm the accuracy of pedicle screw placement. There are no studies to differentiate between solid screws and hollow screws to the electrical resistance of pedicle screws. We speculate that the electrical resistance of the solid and hollow pedicle screws may be different and then a potential source of error with stimulus-evoked EMG may happen.Materials and Methods:Resistance measurements were obtained from 12 pedicle screw varieties (6 screws of each manufacturer) across the screw shank based on known constant current and measured voltage. The voltage was measured 5 times at each site.Results:Resistance of all solid screws ranged from 0.084 Ω to 0.151 Ω (mean =0.118 ± 0.024 Ω) and hollow screws ranged from 0.148 Ω to 0.402 Ω (mean = 0.285 ± 0.081 Ω). There was a significant difference of resistance between the solid screws and hollow screws (P < 0.05). The screw with the largest diameter no matter solid screws or hollow screws had lower resistance than screws with other diameters. No matter in solid screws group or hollow screws group, there were significant differences (P < 0.05) between the 5.0 mm screws and 6.0 mm screws, 6.0 mm screws and 7.0 mm screws, 5.0 mm screws and 7.0 mm screws, 4.5 mm screws and 5.5 mm screws, 5.5 mm screws and 6.5 mm screws, 4.5 mm screws and 6.5 mm screws. The resistance of hollow screws was much larger than the solid screws in the same diameter group (P < 0.05).Conclusions:Hollow pedicle screws have the potential for high electrical resistance compared to the solid pedicle screws and therefore may affect the EMG response during stimulus-evoked EMG testing in pedicle screw fixation especially in minimally invasive percutaneous pedical screw fixation surgery.

The Effect of the TiO2 Anodization Layer in Pedicle Screw Conductivity: An Analytical, Numerical, and Experimental Approach

“…Since this study was performed with direct current, and given the low capacitance of TiO 2 (<4.5 pF) [39], it is reasonable to expect that these capacitors will quickly become open circuits, leading all the current through the resistors. However, a series arrangement would require the sum of the TiO 2 and Ti-6Al-4V resistances, resulting in a larger model resistance and low conductivity, which is not in line with the results of experimental studies [7][8][9]40].…”

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

“…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.…”

“…While some systematic reviews have identified the current thresholds associated to higher sensitivities of this IONM method [8][9][10], there is no complete explanation yet with respect to the high levels of heterogeneity and lack of agreement between studies on the best current stimulation threshold. This is a multifactorial issue caused by the multiple situations that may alter the normal nerve stimulation, which not only includes patient intrinsic aspects such as compressed nerve roots [11] but also extrinsic ones, such as the properties of the pedicle screw [12]. Although pedicle screws have been extensively characterized and analysed in terms of their biomechanical [13] and mechanical properties [14,15], the study of their electrical properties is still scarce.…”

“…Although pedicle screws have been extensively characterized and analysed in terms of their biomechanical [13] and mechanical properties [14,15], the study of their electrical properties is still scarce. 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].…”

“…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.…”