# Measuring Cranivertebral Angle Reference Values in Adults Using Kinovea Software
## 2 Materials and Methods
### Data Collection  
Each eligible participant attended one data collection session at the Universitat Internacional de Catalunya physiotherapy functional assessment room. Following completion of informed consent, the following data were obtained from each participant during an interview: age (years), sex, medication use, presence of neck pain in the last year, presence of neck pain at the time of the interview, hours per day of computer or mobile device screen use, hours per day spent sitting, hours per week of physical activity, presence of impaired vision, and use of dental hardware to manage the presence of bruxism. Participants then completed one digital questionnaire to assess depression and anxiety levels, the Hospital Anxiety and Depression Scale (HADS), and a second digital questionnaire to assess the degree of disability related to neck pain, the Neck Disability Index (NDI) [34, 35].  
The HADS is a scale used to evaluate depression and anxiety. It evaluates a total of 14 items: seven items about anxiety and seven about depression. The scale asks the participant to consider the last week when completing the questionnaire. Each item has four Likert-type options that score from 0 to 3 points, with a higher score representing a greater level of depression and/or anxiety and a maximum score of 42 points. The validated Spanish version has shown a very good reliability with intraclass correlation coefficients (ICC) from 0.85 to 0.91 [36, 37].  
The NDI is a questionnaire with 10 items that score from 0 to 5 based on six response options, with a total possible score of 50 points. This questionnaire evaluates disability based on the impact of neck pain in daily activities and social relationships. The degree of disability is given in accordance with the score. A higher score indicates greater disability. The test demonstrates a high test-retest reliability with ICC 0.88 [35].  
Measurement of the cranivertebral angle was performed using digital image analysis of a lateral view photograph of each participant seated in the same standard chair. The participant was asked to position him/herself in a relaxed posture with the thoracic and lumbar regions contacting the backrest, eye gaze to the horizon, and both feet resting on the floor with their knees flexed 90\({}^{\circ}\). A Sony DSC-W830 camera (Sony Corporation, Tokyo, Japan) was placed one meter from the participant on a level tripod at the participant's shoulder height. To facilitate measurement using the software, a marker was placed with adhesive tape at the level of the C7 vertebra and it was ensured that the tragus of the participant's ear was visible in the photo frame. Identification of the C7 vertebrae was performed using active cervical rotation as described elsewhere [10,38]. The image was analyzed using Kinovea 0.8.15 software, considering the cranivertebral angle as the angle measured between a horizontal line and the line that joins the spinous process of C7 and the tragus of the ear (Figures 1 and 2) [39,40].  
Figure 1: Cranial vertebral angle (CVA) measurement using photograph and digital measurement software.