Pain-side related difference in cross-sectional area of the longus colli muscle and its relationship with standing balance in persons with non-specific neck pain

Longus colli muscle has a significant role in postural control. A reduction of longus colli cross-sectional area (CSA) has been demonstrated in neck pain patients. However, pain-side related difference and its relationship with clinical features and standing balance remain unclear.To investigate side-to-side difference in the longus colli CSA and to determine the relationships of the CSA with clinical characteristics and standing balance in neck pain patients.Cross-sectional study.Fifty participants with chronic non-specific neck pain (20 unilateral and 30 bilateral) were recruited. CSA of the longus colli muscle was measured using ultrasound imaging. Balance was measured using a force platform during a narrow stance with eyes open, eyes closed, and neck torsion (left and right). Balance outcomes were sway area and displacement in anterior-posterior (AP) and medial-lateral (ML) directions. Clinical characteristics were neck pain intensity, disability, and duration.The longus colli CSA was reduced on the painful side in patients with unilateral neck pain (p 0.01). There was a trend towards reduced CSA on the more painful side in those with bilateral neck pain (p = 0.08). The reduced CSA was mostly correlated with the greater AP sway displacement and sway area (r ranged from -0.27 to -0.54, p0.05). The longus colli CSA was not correlated with pain intensity, disability, and duration (p 0.05).The longus colli CSA was reduced on the painful side of neck pain. The reduced CSA was correlated with impaired standing balance, but not with clinical characteristics of neck pain.