We aimed at investigating the morphological difference of the rotator cuff (RC) muscles among age groups from elementary school students to college students. The subjects included 10 college (22.6 ± 1.8 years), 10 high school (16.8 ± 0.6 years), 10 junior high school (13.9 ± 0.6 years), and 10 elementary school (10.4 ± 0.5 years) students. Consecutive oblique sagittal magnetic resonance T1-weighted images of the dominant shoulder were acquired for each participant. Muscle length, maximal anatomical cross-sectional area (ACSA), the position of the maximal ACSA at full muscle length, muscle volume, and the individual-to-total RC muscle volume ratio for the supraspinatus, external rotators (infraspinatus and teres minor), and subscapularis were evaluated. The muscle length, maximal ACSA, and muscle volume in the RC muscles significantly increased with increasing age (P < 0.01), but there was no significant difference between college and high school students except in regard to the volume of the external rotators. There was no difference in the position of the maximal ACSA or the individual-to-total RC muscle volume ratio among the groups. The findings of this study show that the size of each RC muscle increases with increasing age, but the position of maximal ACSA and the proportion of each muscle to the total RC muscle volume are similar among age groups from elementary school students to college students.
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