Greater muscle fat infiltrate in the cervical spine extensor muscles in individuals with chronic idiopathic neck pain compared to matched asymptomatic controls: a cross-sectional study

Muscle composition (muscle volume and muscle fat infiltrate [MFI]) may provide insight into possible mechanisms underpinning chronic idiopathic neck pain, a common condition with no definitive underlying pathology. In individuals with chronic idiopathic neck pain > 3 months and age- and sex-matched asymptomatic controls, muscle volumes of levator scapulae, multifidus (including semispinalis cervicis), semispinalis, splenius capitis (including splenius cervicis), sternocleidomastoid and longus colli from C3 through T1 were quantified from magnetic resonance imaging, with between-group differences determined using linear mixed models, accounting for side (left or right), muscle, spinal level, sex, age, and body mass index (BMI). Individuals with pain had greater muscle volume (mean difference 76.8mm 3 ; 95% CI 26.6–127.0; p = .003) and MFI (2.3%; 0.2–4.5; p = .034) of the multifidus compared to matched controls with no differences in relative volume, accounting for factors associated with the outcomes: muscle, spinal level, side (left had smaller volume, relative volume and MFI than right), sex (females had less volume and relative volume than males, age (older age associated with less relative volume and greater MFI), and BMI (higher BMI associated with greater muscle volume and MFI). Greater MFI in individuals with chronic idiopathic neck pain suggests a possible underlying mechanism contributing to neck pain. Perspective: These findings suggest MFI in the multifidus may be radiologic sign, potentially identifying patients with a less favourable prognosis. Future studies are needed to determine if MFI is a contributor to the development or persistence of neck pain, or consequence of neck pain.