The Association between the Magnetic Resonance Imaging Findings of Adhesive Capsulitis and Shoulder Muscle Fat Quantification Using a Multi-Echo Dixon Method

Objective: To investigate the association between the magnetic resonance imaging (MRI) findings of adhesive capsulitis and shoulder muscle fat percentages using a multi-echo Dixon method. Materials and Methods: Twenty-four patients with clinical diagnoses of adhesive capsulitis and either intact rotator cuffs or Ellman grade 1 partial tears as indicated by MRI scans were included. Two radiologists independently evaluated MRI scans of adhesive capsulitis as follows: presence or absence of axillary recess capsular and extracapsular hyperintensities; thickness of the coracohumeral ligament; thickness of abnormal rotator interval soft tissue; and thickness of glenoidal/humeral axillary recess capsules. Fat quantifications of the supraspinatus, infraspinatus, teres minor, subscapularis, teres major and posterior deltoid muscles were performed using multi-echo Dixon imaging at three locations. Inter-rater agreement was assessed. Differences in fat percentages were assessed and correlations between fat percentages and quantitative measurements were evaluated. Results: The fat percentage of the supraspinatus was significantly higher in patients with extracapsular hyperintensity (present, $3.00{\pm}1.74%$; absent, $1.81{\pm}0.80%$; p = 0.022). There were positive correlations between the fat percentage of the teres minor and the thicknesses of the abnormal rotator interval soft tissue (r = 0.494, p = 0.014) and the glenoidal axillary recess capsule (r = 0.475, p = 0.019). After controlling for the effects of age, sex and clinical stage, the relationship between the teres minor fat percentage and the thickness of the abnormal rotator interval soft tissue was statistically significant (r = 0.384, p = 0.048). Inter-rater agreement was almost perfect for fat quantification (intraclass correlation coefficients [ICC] > 0.9) and qualitative analyses (k = 0.824), but were variable for quantitative measurements (ICC, 0.170-0.606). Conclusion: Several MRI findings of adhesive capsulitis were significantly related to higher fat percentages of shoulder muscles.