Does humeral retrotorsion affect glenohumeral rotation and stiffness of posterior shoulder in college baseball pitchers?

Decreased internal rotation range of motion of the dominant shoulder in baseball pitchers may be due to humeral retrotorsion and posterior shoulder tightness. Measurement of shoulder tightness is generally performed with range of motion; however, this may not be optimal for measuring posterior shoulder tightness in baseball pitchers. Joint stiffness using passive torque should also be used to assess shoulder tightness. The purpose of this study was to compare dominant and non-dominant shoulder humeral retrotorsion and shoulder tightness in baseball pitchers, and dominant and non-dominant shoulder range of motion and shoulder stiffness of the passive torque after correction based on humeral retrotorsion. Twenty-five male college baseball pitchers were included. Humeral retrotorsion, shoulder range of motion (internal rotation, external rotation, total range of motion), and passive torque during shoulder internal rotation (max torque, stiffness) of the dominant and non-dominant sides were measured. Shoulder range of motion and stiffness were corrected on each side using humeral retrotorsion. Humeral retrotorsion, external rotation range of motion, and stiffness were significantly greater on the dominant side than on the non-dominant side. Internal rotation range of motion was reduced on the dominant side compared to the non-dominant side. There were no side-to-side differences in the total range of motion, humeral retrotorsion-corrected range of motion, and humeral retrotorsion-corrected stiffness. In conclusion, healthy college baseball pitchers have decreased internal rotation range of motion in the dominant shoulder due to side-to-side differences in humeral retrotorsion, not joint stiffness.