Quantifying cervical and axioscapular muscle stiffness using shear wave elastography.

This study aimed to assess intra-rater (intra-session and inter-day) reliability and influence of side dominance and the scapular resting position on the shear modulus (an index of stiffness) of resting cervical and axioscapular muscles. Sixteen healthy participants were recruited. On day one, ultrasound shear wave elastography was used to measure the shear modulus of superficial and deep cervical extensor and axioscapular muscles bilaterally. Clinical assessments of scapular resting position were performed bilaterally. On day two, testing was repeated on the dominant side. Both intra-session and inter-day reliability were good to excellent for shear modulus of superficial muscles, and poor to excellent for deep muscles. Side differences of shear modulus for posterior upper trapezius were statistically significant but clinically irrelevant. The shear modulus of posterior upper trapezius and middle trapezius were significantly correlated with scapular depression. Ultrasound shear wave elastography is a reliable tool for quantitatively assessing stiffness of superficial cervical and axioscapular muscles. The influence of scapular position should be considered in future comparative studies of healthy controls and patients with neck/shoulder pain. This study provides the necessary first step for future studies on assessing and interpreting the stiffness of cervical and axioscapular muscles for neck and shoulder musculoskeletal disorders.