Fig. 2.

Measurement of segmental motion. (A) Segmental translation. A base line is drawn at the superior endplate of lower vertebra. Also, the perpendicular line to the base line at the posteroinferior corner of the upper vertebra is drawn on the flexion and extension radiograph. The difference (arrow) is calculated. (B) Segmental angulation. The angle between the line on the upper endplate of lower vertebra and the line on the lower endplate of upper vertebra is measured on flexion and extension radiographs. In addition, the difference (B-A) is calculated.