Figure 1 The CL, CDH, and CDA measurement methods in lateral X-ray images. (A) CL was defined as the angle formed by the lower endplates of C2 and C7, with lordosis defined as positive and kyphosis defined as negative. (B) CDAH was defined as the distance between the anterior point of the endplates, CDMH was defined as the distance between the middle point of endplates, and CDPH was defined as the distance between the posterior point of endplates, while CDH=(CDAH+CDMH+CDPH)/3. (C) The CDA was defined as the angle formed by the endplates of the upper and lower vertebrae.