Evaluation of Safety of Complex Pedicle Screw Trajectories Using Patient-Specific Guides (MySpine, Medacta) (Red Screws)

This retrospective, single-center observational study evaluates the clinical safety and neurophysiological performance of patient-specific MySpine guides (Medacta International) for pedicle screw placement in patients undergoing instrumented spinal surgery. Particular attention is focused on anatomically complex trajectories identified during preoperative planning as "Red Screws," in which complete osseous containment of the planned screw trajectory cannot be ensured because of dysplastic, hypoplastic, or otherwise challenging pedicle anatomy.

The study includes 130 patients treated between January 2015 and January 2026, encompassing a total of 2,626 pedicle screws. The primary objective is to compare the incidence of positive triggered electromyography responses, defined as a stimulation threshold <8 mA, between standard screws and Red Screws.

Secondary objectives are to compare absolute stimulation thresholds, screw-related intraoperative neuromonitoring alerts, the need for screw repositioning or removal, and postoperative neurological deficits considered related to screw placement. An exploratory analysis will also investigate whether a planned medial cortical breach is associated with an increased risk of neurophysiological warning signals or other intraoperative screw-related events.