Evaluating serratus anterior muscle function in neck pain using muscle functional magnetic resonance imaging

Muscle functional magnetic resonance imaging (mfMRI) quantifies exercise-induced alterations in soft-aqueous skeletal muscle as a surrogate measure of muscle activity. Because of its excellent spatiotemporal resolution, mfMRI can be used as a noninvasive evaluation of the function of muscles that are challenging to evaluate, such as the serratus anterior (SA) muscle. The purpose of this preliminary study was to investigate the feasibility of evaluating SA muscle function in individuals with neck pain compared with healthy controls using mfMRI.

Muscle functional magnetic resonance imaging scans of the SA muscle were obtained before and immediately after an isometric upper limb exercise in 10 subjects with chronic ipsilateral mechanical neck pain and scapular dysfunction (scan on symptomatic side) and in 10 age- and sex-matched healthy subjects. Scans were recorded at 4 intervertebral levels (T6-7, T7-8, T8-9, and T9-10). Differences in water relaxation values (T2 relaxation) quantified from scans before and after exercise were calculated (T2 shift) as a measure of SA muscle activity at each level and compared between groups.

There were significant effects for level (P = .03) and significant group × level interactions (P = .04) but no significant main effect for group (P = .59). Post hoc tests revealed that significant differences in T2 shift values between levels were only evident in the healthy control group.

This study demonstrated that despite some inherent challenges associated with imaging the SA muscle, mfMRI appears to have adequate spatiotemporal resolution to effectively evaluate SA muscle activity and function in healthy and clinical populations.