Experimental Characterization of Transient G-Forces in Spinal Fixation During Set Screw Failure

Abstract

Abstract. Pedicle screw fixation systems are essential for spinal stabilization, yet the transient g-forces generated during manual set screw torquing, a critical phase with implications for implant stability, remain poorly understood. This study employs a multimodal experimental approach to quantify these dynamic forces and validate theoretical torque failure models. A sawbone spinal construct was instrumented with accelerometers at biomechanically strategic locations (screw head, spinal center, contralateral pedicle, and surrounding media) to capture transient accelerations during screw fracture. High-speed imaging (40,000 fps) and motion tracking complemented accelerometer data, while distortion energy theory (DET) and fully plastic torque (FPT) models predicted break-off torque. Results revealed extreme g-forces (up to 832 g) localized at the screw head, attenuating rapidly (20-fold reduction at the spinal center). Theoretical predictions (DET: 11.08 N·m; FPT: 11.1 N·m) aligned closely with experimental torque wrench measurements (11.3 N·m, <1.3% error), validating analytical models. Digital image analysis confirmed screw geometry precision (<1.3% error). While the rigid sawbone model limited physiological fidelity, findings emphasize the localized stress propagation and energy dissipation during screw failure, critical for optimizing implant designs, particularly in osteoporotic bone. This integrated methodology bridges biomechanical theory and experimental validation, offering actionable insights to mitigate screw loosening risks and enhance spinal construct durability. Future work will focus on advanced synthetic bone analogs and clinical correlation to refine translational relevance.