Fig. 2.

Radiographs illustrating how to measure the range of motion (ROM). The ROM of the whole cervical spine is defined as the difference in the Cobb's angle of C2-C7 between the flexion and extension view (A°). The ROM of upper adjacent segment (B°) and lower adjacent segment (C°) is defined as the difference in the Cobb's angle of adjacent level in the treated unit between the flexion and extension view. The ROM of arthroplasty level is calculated in the dynamic lateral simple radiographs (D°).