Reduced Cervical Muscle Fat Infiltrate Is Associated with Self-Reported Recovery from Chronic Idiopathic Neck Pain Over Six Months: A Magnetic Resonance Imaging Longitudinal Cohort Study

Background: It is unclear why neck pain persists or resolves, making assessment and management decisions challenging. Muscle composition, particularly muscle fat infiltrate (MFI), is related to neck pain, but it is unknown whether MFI changes with recovery following targeted interventions. Methods: We compared muscle composition quantified from fat-water magnetic resonance images from the C3 to T1 vertebrae in individuals with and without chronic idiopathic neck pain at two times 6 months apart. Those with neck pain received six weeks of intervention (physiotherapy or chiropractic) after their baseline MRI; at 6 months, they were classified as recovered (≥3 on the 11-point Global Rating of Change scale) or not recovered. Results: At 6 months, both asymptomatic and recovered individuals had decreased MFI compared to baseline (asymptomatic estimated marginal mean difference −1.6% 95%; CI −1.9, −1.4; recovered −1.6; −1.8, −1.4; p < 0.001) whereas those classified as not recovered had increased MFI compared to baseline (0.4; 0.1, 0.7; p = 0.014), independent of age, sex and body mass index. Conclusions: It appears MFI decreases with recovery from neck pain but increases when neck pain persists. The relationship between cervical MFI and neck pain suggests MFI may inform diagnosis, theragnosis and prognosis in individuals with neck pain. Future development of a clinical test for MFI may assist in identifying patients who will benefit from targeted muscle intervention, improving outcomes.