Experimental study of the influence of different intrinsic properties of pedicle screws on the electrical resistance

English Keywords:Pedicle screw  Electrical resistance  Spine  Diameter  Solid  Cannulated

English Abstract:

  【Abstract】 Objectives: To study the influence of pedicle screw structural features(solid and cannulated pedicle screws, diameters) on the electrical resistance of pedicle screws and to discuss its possible effect on the accuracy of pedicle screw insertion monitored by stimulus-evoked electromyography. Methods: Electrical resistance measurements were obtained from 12 pedicle screw varieties(6 screws of each manufacturer: solid or cannulated pedicle screws with diameter of 5.0mm, 6.0mm, 7.0mm in Johnson company and solid or cannulated pedicle screws with diameter of 4.5mm, 5.5mm, 6.5mm in Medtronic company) across the screw shank with an interval of 20mm based on measured constant current and voltage using potentiometer and multimeter according to Ohm′s law. Results: Electrical resistance of pedicle screws with 4.5mm, 5.5mm, 6.5mm in diameter was (0.142±0.003)Ω, (0.110±0.007)Ω, (0.086±0.002)Ω in solid pedicle screws respectively and (0.398±0.002)Ω, (0.347±0.003)Ω, (0.290±0.003)Ω in cannulated pedicle screws respectively from Johnson company. Electrical resistance of pedicle screws with 5.0mm, 6.0mm, 7.0mm in diameter was (0.149±0.001)Ω, (0.123±0.004)Ω, (0.095±0.001)Ω in solid pedicle screws and (0.291±0.001)Ω, (0.237±0.001)Ω, (0.148±0.001)Ω in cannulated pedicle screws got from Medtronic company, and the electrical resistance of cannulated screws was much higher than that of solid screws in the same diameter group(P<0.05). The screw with largest diameter had lower electrical resistance than the screws with shorter diameters, whether solid screws or cannulated screws(P<0.05). Conclusions: Cannulated pedicle screws have higher electrical resistance compared to the solid pedicle screws with the same length and diameter, smaller diameter pedicle screws have higher electrical resistance compared to the larger diameter pedicle screws, we should pay much attention to its influence when stimulus-evoked electromyographic test was used in placing pedicle screw.