The geometric changes of acute thoracolumbar burst fractures under extension and traction loadings ware analyzed using functional radiographs. The injuries were produced in an in vitro high-speed impact model. The changes in nine geometric parameters, (three angular and six linear) were analyzed from neutral posture to extension and traction positions. In the extended position, all parameters, except the posterior vertebral height and vertebral diameter, were significantly different from the neutral posture values. Also in extension, the posterior vertebral height, vertebral diameter, and posterior unit height were significantly different from their intact values. In the traction position, all nine geometric parameters changed significantly from the neutral posture, whereas only the vertebral diameter remained significantly different from its intact value. These finding a demonstrated the treatment advantages of applying traction force to acute burst fractures in contrast to extension moments. Further, changes in the angular parameters due to motion from neutral to extension posture demonstrated that the acute flexibility of the three-vertebrae segment was contributed a meat equally by the upper disc (35%), lower disc (27%) and fractured vertebra (38%).