Evaluation of the intrinsic properties of pedicle screws: Do diameter, manufacturing and screw design affect resistance and/or resistivity

Abstract

The pedicle screw diameter, composite and design are variables that can aff ect the threshold of intraoperative electromyographic monitoring. Even though we know that larger diameter objects tend to have less resistance, no study documented the eff ect that this variable could have on pedicle screw resistance. Using high quality equipment, resistance and resistivity of ten pedicle screws (from four manufacturers) were calculated based on known constant current and measured voltage. Voltage was measured three times for each screw to determine intraobserver measurement variability. Resistance of all screws ranged from1.4 to 3.9 mΩ (mean = 2.69±0.71 mΩ). The screw with largest diameter (7.75 mm) had lower resistance than screws with other diameters. Resistivity of screws ranged from 7.12 to 12.63 μΩ•m (mean = 9.9±1.82 μΩ•m). Based on the screw design, one manufacturer's pedicle screws (A) had significantly lower resistivity compared to three other manufacturers (p<0.01). Larger diameter screws (7.75 mm in diameter) had lower resistance. Screw design (polyaxial or monoaxial) had no eff ect on its resistance. Screws of one manufacturer (A) showed lower resistivity compared to those manufactured by other three companies.