Ultrasound imaging of the diagonal dimension of the deep cervical flexor muscles: A reliability study on healthy subjects.

The purpose of this study is to assess the reliability of a new ultrasound imaging (USI) parameter and procedure for the evaluation of the size of the deep cervical flexor (DCF) muscles. Thirty-one healthy male subjects (21.6 ± 2.5 years old) participated in this study. Two images of the diagonal dimension (DD) of the DCF of the subjects, at 1.5 fingerbreadths below the laryngeal prominence of the thyroid cartilage in a relaxed state, were taken on separate days with a 1-week interval. The intraclass correlation coefficient between the days was 0.82 (95% confidence interval, 0.65-0.91). The standard error of measurement and minimal detectable change were 0.8 mm and 2.1 mm, respectively. The results indicated that the DD may be used as a reliable USI parameter to measure the DCF thickness in healthy subjects.