Little Leaguer's Shoulder Can Cause Severe Three-Dimensional Humeral Deformity.

We analyzed three-dimensional (3D) humeral deformity (valgus-varus, flexion-extension, and rotational deformation) after little leaguer's shoulder using 3D computed tomography in a 15-year-old male baseball player. Humeral retroversion was increased by 27.1° on the dominant side compared with the nondominant side. Compared with the nondominant shaft, the dominant humeral shaft was deformed in the varus direction (9.4°), resulting in a decreased neck-shaft angle (dominant side, 127.5°; nondominant side, 135.1°), and it was also deformed in the extension direction (21.0°). This case demonstrates that little leaguer's shoulder can cause markedly greater humeral retroversion than has been reported previously and can result in varus and extension deformation of the humerus. These findings suggest that humeral deformity in overhead throwing athletes may not always solely reflect adaptation to throwing.