Cross-sectional areas of rotator cuff muscles in males without tears on shoulder MRI

Objective To establish reference values of rotator cuff (RC) cross sectional area (CSA) in males. Materials and methods We retrospectively analyzed shoulder MRIs from 500 patients aged 13-78 years, grouped as follows ( N =100 in each): <20, 20-30, 30-40, 40-50, >50 years. All examinations were reviewed to exclude prior surgery, tears, or significant RC pathology. We segmented a standardized T1 sagittal MR image in each case to obtain CSA of supraspinatus (SUP), infraspinatus/teres minor (INF), and subscapularis (SUB) muscles. Across age groups, we recorded individual and total muscle CSA. We also performed ratios between individual muscle CSA and total CSA to examine total muscle mass contribution over age groups. We tested for differences between age groups controlled for BMI. Results CSAs for SUP, INF, SUB, and total RC CSA were lower in subjects >50 years compared to all other groups ( P <0.003 for all comparisons), persisting after controlling for BMI ( P <0.03). Relative contribution of SUP CSA to total RC CSA was stable across age groups ( P >0.32). INF CSA relative to total RC CSA increased with age, whereas SUB decreased ( P <0.005). Subjects >50 years showed lower SUP (-15%), INF (-6%), and SUB (-21%) CSA, when compared to mean CSAs of all subjects <50 years. Total RC CSA significantly correlated with age (r=-0.34, P <0.001), persisting after controlling for BMI (r=-0.42, P <0.001). Conclusion RC muscles in male subjects with no tears on MRI show decreasing CSA with age, independent of BMI.