Spinal Compression Fracture Mechanisms in Mountain Biking: An Accident Reconstruction Approach

Study DesignBiomechanical Simulation Study.ObjectivesSpinal injuries account for 30-40% of severe mountain biking (MTB) cases and may be mitigated by back protectors. Thoracolumbar compression fractures are linked to rolling impacts during forward falls, yet their biomechanical mechanisms remain poorly understood. It is unclear whether current back protectors, tested under perpendicular conditions (EN1621-2), adequately address the complex loading of real-world crashes.This work aims to investigate the biomechanical mechanisms of thoracolumbar fractures during MTB forward falls.MethodsForty-four back-impact scenarios were simulated using a THUMS V4 finite element model, based on velocities derived from prior multibody simulations. The analysis examined the effects of impact velocity, angle, friction, and body position on spinal loading and fracture pathways. Injuries were predicted using force, moment, stress, and strain.ResultsVertebral fractures were predicted in 84% of cases, occurring away from the impact site due to combined axial loading and hyperflexion. Three mechanical pathways leading to Magerl type A fractures were identified: (1) 45° lower-back impacts causing thoracolumbar (T12-L2) fractures; (2) flat (0°) lower-back impacts causing upper-thoracic injuries; and (3) upper-back impacts leading to lumbar (L4-L5) fractures through "whiplash-like" motion. Normal velocity was the strongest injury risk predictor, while impact angle determined fracture location.ConclusionSimulated fractures were not predicted at the impact site but at a distance, driven by combined axial loading and hyperflexion induced by normal and rotational velocities. Current back protector testing protocols do not reflect these mechanisms and may not adequately address real-world spinal loading conditions.