Relationship between cervical curvature index (Ishihara) and cervical spine angle (C2–7)

Abstract

The purpose of this study was to determine the relationship between the cervical curvature index (Ishihara) and the cervical spine angle (C2–7) from both cervical lateral radiographs and a geometrical model. The cervical lateral radiographs of 295 outpatients with no cervical symptoms were reviewed to measure the cervical curvature index (Ishihara) and the cervical spine angle (C2–7). The average cervical curvature index (Ishihara) was 10.9 (SD, 15.3) and the average cervical spine angle (C2–7) was 20.3 (SD, 14.3). A highly significant correlation (0.95; 95% confidence interval [CI], 0.94–0.96) was found between the cervical curvature index (Ishihara) and the cervical spine angle (C2–7). Their linear correlation was also validated in the geometrical model. Their correlation diminished, however, in subjects with an S-shaped cervical spine. The cervical curvature index (Ishihara) and the cervical spine angle (C2–7) were interchangeable, but this interchangeability was lost in the S-shaped cervical spines.