Humeral retrotorsion and age-related increase in GIRD
Internal rotation ROM and glenohumeral rotation deficits (GIRDs) are related with age, but there is still unclarity regarding their origin: either soft tissue adaptations or changes in the osseous anatomy of the humerus.
To better understand the underlying factors contributing to changes in the rotational spectrum of the shoulder, this study investigated the influence of age group on GIRD, humeral torsion, torsion-adjusted GIRD and total ROM of youth and adolescent baseball players. In 287 players ranging from 6 to 18 years of age, rotational ROM and humeral torsion were determined.
Subjects had less internal rotation ROM, greater humeral torsion and (surprisingly!) greater torsion-adjusted internal rotation ROM on the dominant side compared with the nondominant side; no differences in total ROM were present between sides. While GIRD and humeral torsion increased with age in the youngest three groups, no differences were present in the oldest two groups. No differences in adjusted GIRD or total rotational ROM were present between all groups. These results suggest that increases in internal rotational ROM with age are due to changes in morphology of the humerus.