Fig. 1.

The horizontal distance 1, 2, 3, and 4 were measured by using the lateral view of cervical spine X-ray. Distant 1 was the horizontal distance between the earhole and lateral shoulder. Distant 2 was the horizontal distance between plump line of posterior neck and posterior shoulder. Distant 3 was the horizontal distance between the anterior margin of C1 body and the posterior margin of C7 spinous process. Distant 4 was the horizontal distance between the earhole and midline of C7 lower margin.