Trajectory tracking made simple: validating a low-cost IMU pedicle screw guide

Pedicle screw fixation is central to spinal stabilization, but its accuracy depends on precise trajectory alignment. Freehand placement has a steep learning curve, with breach rates of 1.7-6.2%. Navigation and template systems improve precision but are costly. This study aimed to validate a low-cost inertial measurement unit (IMU)-based guide for pedicle screw trajectory tracking using lumbosacral saw bone models.

A prospective experimental study was conducted on five lumbosacral saw bone models (60 screws). Pre-procedural CT planning determined ideal axial angles through the pedicle axis. A custom IMU assembly (MPU-925x™, Arduino Uno) provided real-time axial orientation. Screws were inserted at the superior facet-transverse process (SF-TP) junction under IMU guidance. Post-insertion CT assessed achieved angles and cortical breaches.

Sixty pedicle screws were placed. Planned axial angles ranged 11°-30° (mean 22.6° ± 4.5°), while achieved angles averaged 25° ± 7.4°. The mean angular offset was 2.23° ± 6.5°. Pedicle containment was achieved in 54/60 screws (90%), with overall containment fidelity of 96.7% (58/60). Six screws (10%) exhibited cortical breaches, of which two (3.3%) were significant (> 2 mm). Trajectory fidelity (offset < 10°) was achieved in 83.3% (50/60) screws. Breach orientation correlated with offset magnitude, with medial breaches showing greater angular deviation.

IMU-guided pedicle screw insertion demonstrated high containment and trajectory fidelity in simulated models, supporting further cadaveric evaluation of low-cost orientation-tracking systems.