The differences of humeral torsion angle and the glenohumeral rotation angles between young right-handed and left-handed pitchers

Background: The differences between young right-handed and left-handed baseball players are not well known. This study compared the range of the shoulder motion and humeral torsion angle (HTA) between right-handed and left-handed young baseball pitchers. Methods: A total of 65 young baseball pitchers (age, 9-12 years; 46 right-handed throwers, R group; and 19 left-handed throwers, L group) were analyzed. The glenohumeral internal rotation (IR) angle and external rotation (ER) angle were measured at 90 degrees shoulder abduction, and HTA was assessed using indirect ultrasonographic techniques. The side-to-side difference in HTA (d-HTA), glenohumeral ER difference (GERD), and glenohumeral IR deficit (GIRD) were calculated. The adjusted GIRD and adjusted GERD were defined as the angles obtained by subtracting d-HTA from GIRD and GERD, respectively, to exclude the influence of humeral retrotorsion difference. Results: HTA and ER of the throwing limb were significantly greater than those of the nonthrowing limb in the R group (HTA: 84 degrees vs. 77 degrees; P < .001, ER: 116 degrees vs. 111 degrees; P < .001), but no significant differences were observed in the L group (HTA: 79 degrees vs. 77 degrees, P = .103; ER: 113 degrees vs. 114 degrees, P = .380). Compared with the R group, the L group showed a significantly smaller d-HTA(2 degrees vs. 8 degrees, P < .001) and GERD (5 degrees vs. -2 degrees, P = .004), but no significant difference was observed in adjusted GERD between the groups (-3 degrees vs. -4 degrees, P = .690). Conclusion: Compared with the right-handed pitchers, the side-to-side differences of glenohumeral external rotation angle and humeral torsion angle were significantly smaller in the left-handed pitchers at a young age. (C) 2019 Published by Elsevier Inc. on behalf of Journal of Shoulder and Elbow Surgery Board of Trustees.