Pedicle screw instrumentation as part of spine surgery is a recurrent technique used for most of spine surgeons. Since its description by Boucher in 1959 and its popularization later by Roy-Camille, has been considered a technique that demands great anatomy knowledge and some grade of expertise. Even in experienced hands the misplacement of pedicle screws could have an incidence of 10-40% (average of 20%). Medially misplacements during track creation and screw insertion are the most feared complications, because the anatomic relationship between medial pedicle wall and neural structures. The first attempt to use continuous electrical stimulation during pedicle track creation and screw insertion was communicated in 1997 by Welch WC, et al. In that study they used the bone impedance as a direct measurement of pedicle wall integrity; unfortunately they used inhaled anesthetics and assessed the final screw position with plain X-rays. They reported a sensibility and specificity of 98% and 99% respectively. The great limitation for this study is its assessment of screw accuracy performed by plain X-rays, now a days the best way to do it is with computed tomography (CT).