Pretapping is Not Effective in Preventing Pedicle Fractures in Lumbar Spinal Instrumentation: A Biomechanical Cadaveric Study.

Abstract

Biomechanical cadaveric study. To evaluate whether pre-tapping reduces the risk of pedicle fractures following pedicle screw instrumentation. Pedicle screw instrumentation is the standard for rigid fixation of the thoracolumbar spine. While complications such as screw loosening and misplacement are well-documented, pedicle fractures are rare and poorly understood. Pre-tapping, a technique used during screw insertion, has been proposed to enhance fixation strength and potentially reduce the risk of fractures. However, its biomechanical effects on pedicle integrity remain unclear. Twenty lumbar vertebrae (L1-L5) were harvested from four cadavers. Preoperative CT scans were used to plan screw trajectories and assess bone mineral density (BMD). Each vertebra was alternately instrumented with screws using pre-tapping and non-pre-tapping techniques. Biomechanical testing measured maximum bending force to failure under a flexion moment. Pedicle fractures were classified based on CT imaging, and statistical analysis was performed to evaluate factors influencing fracture risk. The maximum bending force to failure showed no significant difference between pre-tapping (103.9±47.5 Nm) and non-pre-tapping (98.1±43.4 Nm) groups (P=0.321). Pre-tapping significantly reduced maximum insertion torque (1.30±1.05 Nm vs. 2.91±2.65 Nm, P=0.025). Pedicle fill was a significant predictor of bending force (β=222.29 Nm, P=0.035), while BMD and pedicle diameter were not. Fracture patterns did not differ significantly between groups (P=0.384). Pre-tapping does not significantly influence the biomechanical stability of pedicle screws or the risk of pedicle fractures under flexion moments. However, pedicle fill is a critical factor in screw fixation strength. These findings suggest that optimizing pedicle fill is more relevant than pre-tapping in enhancing construct stability.