Study Design: Clinical trial. Objective: To compare the efficacy of a commercially available stimulating pedicle probe with a custom-made probe for the detection of pedicle wall breaches during screw insertion for the surgical correction of scoliosis. Summary of Background Data: Stimulus triggered electromyography has been used to detect small breaches in the walls of the spinal pedicles during pedicle screw insertion. We routinely use a reusable, custom-made clip that can be attached to the screw, pedicle probe, or other instruments. Commercial systems are available in which the instrument is electrically instrumented to deliver current. Methods: In five patients (173 pairs of tests), we compared the threshold current required to trigger an electromyographic response during testing of the pedicle. Each track or screw was tested with both the custom-made and the commercial probe and the threshold current recorded. Results: Both systems were able to detect pedicle wall breaches using triggered electromyography. The threshold current recorded was not significantly different between the two systems (P > 0.1, paired t test) nor was the difference (0.16 mA) clinically significant. Conclusion: No difference was found between the thresholds detected with either system. There is however, a significant difference in the costs of the two probe systems.