Spinal injuries due to high-speed trauma are significant problems. The method of treatment depends on the stability determination of the injured spine. Young pig spines were injured at high speed to produce clinically relevant fractures and dislocations. The injuries were produced by dropping a mass onto the superior vertebra and causing three major types of trauma: flexion-compression, extension-compression, and pure compression. The multidirectional instability of each spine was measured before and after trauma by applying pure moments to the three vertebrae segments. Lateral radiographs were taken of each intact and injured spine. Flexion trauma produced the greatest instabilities in flexion and extension, while extension trauma produced the greatest instabilities in axial rotation and lateral bending. Lateral radiographs were found to be inaccurate predictors of spinal instability.