Objective: The aim of this study was to investigate bilateral differences in the cross-sectional area (CSA) and shape ratio of the longus colli muscle between subjects with mechanical neck pain and healthy controls.
Design: A case-control cohort study was conducted. Bilateral ultrasound images of the longus colli muscle at the thyroid (C5-C6) level were conducted in 20 patients with mechanical bilateral chronic neck pain and 20 controls by an assessor blinded to the subjects' condition. CSA, anterior-posterior dimension (APD), lateral dimension (LD), and shape ratio (LD/APD) were measured.
Results: The intraclass correlation coefficients (3,1) were above 0.86 for within-day and above 0.81 for between-day intraexaminer reliability. Patients with mechanical neck pain showed bilateral smaller CSA (P < 0.001) and APD (P = 0.004) as compared with controls. Muscle shape and LD were not different between groups (P = 0.092 and P = 0.963, respectively). Women exhibited smaller bilateral CSA as compared with men (P < 0.01). CSA was negatively associated with self-reported disability, whereas APD was negatively associated with intensity of neck pain: the greater the self-reported disability or the pain intensity, the smaller the bilateral CSA or APD of the longus colli muscle.
Conclusions: The longus colli muscle exhibited smaller bilateral CSA and APD, but not LD and shape ratio, in subjects with bilateral chronic neck pain as compared with healthy controls. Reduced CSA was negatively associated with self-reported disability and APD was negatively associated with the intensity of pain.