An x-ray study technique to detect abnormal vertebral alignment       as seen on a side view x-ray of the neck. The back-side edges of the vertebral bodies are connected with a continuous line. In a normal study, there is a smooth curving line. In an abnormal study there is an abrupt jog or offset in the line to an anterolisthesis or retrolisthesis position. If there is a sharp break in the line, or a stepping effect, this could be a sign of fracture, dislocation or gross ligamentous instability.