Relationship between Cervical Range of Motion in Sagittal Plane and Changes in Cranial Vertical and Cranial Rotation Angles

Background The cranial vertical angle (CVA) and cranial rotation angle (CRA) are widely used photographic indices of head and neck alignment. Although both are commonly employed to assess static posture, little is known about how CRA and CVA change during sagittal plane motion of the head and neck. Purpose This study aimed to investigate the relationship between sagittal plane cervical range of motion (ROM) and dynamic changes in CRA and CVA. Study design Cross sectional study Methods Eighteen healthy individuals without neck pain participated. Cervical flexion and extension ROM was measured using the Cervical Range of Motion device, while changes in CRA and CVA were obtained from photographic images analyzed with ImageJ software. Change values in CRA and CVA were calculated as the difference between the resting and ending postures for each direction of motion. Each measurement was repeated three times per motion direction. Pearson’s correlation analyses were performed to assess the relationships between cervical ROM and changes in CRA and CVA. Results During flexion, cervical ROM showed strong positive correlations with CVA (r=0.86, p<0.01) and CRA+CVA (r=0.96, p<0.01), while CRA alone was not significantly correlated with CVA. During extension, cervical ROM was significantly correlated with CRA (r=0.54, p<0.05), CVA (r=0.71, p<0.05), and CRA+CVA (r=0.85, p<0.01). The combined angular change (CRA+CVA) demonstrated the strongest association with cervical ROM in both flexion and extension. Conclusions Evaluating CRA and CVA together provides a more comprehensive reflection of cervical sagittal mobility than assessing either angle individually. Future research should explore methods for estimating upper and lower cervical ROM separately based on CRA and CVA changes.