LAUSR

BACKGROUND Previous studies have reported that glenohumeral internal rotation deficit (GIRD) may increase the risk of throwing shoulder injuries. The purpose of this study was to analyze the conditions of throwing shoulder in professional baseball pitchers with GIRD by comparing with those in pitchers without GIRD. METHODS In total, 26 male professional baseball pitchers participated in this study. We evaluated the passive range of motion (ROM) and isometric muscle strength at internal rotation (IR) and external rotation (ER) at 90° abduction, as well as the muscle thickness of the supraspinatus (SSP) and infraspinatus (ISP) by ultrasound. The pitchers were divided into two groups as follows: GIRD group who exhibit a loss of 20° or more in the throwing shoulder IR2, and the remaining participants who did not, in the non-GIRD group. RESULTS In the GIRD group, the total range of motion (TRM) deficit (throwing - non-throwing) (p < 0.001), the muscle thickness ratio (throwing:non-throwing) of the SSP and ISP (p = 0.017 and p = 0.014, respectively), and the muscle strength ratio (throwing:non-throwing) of ER (p = 0.028) were significantly lower than those of the non-GIRD group. In contrast, the muscle strength ratio (throwing:non-throwing) of the IR (p = 0.0064) in the GIRD group was significantly higher than that in the non-GIRD group. CONCLUSIONS We showed that GIRD had significant correlations with several conditions, such as atrophy of the SSP and ISP, weakness of ER strength, enhancement of IR strength, limitation of the TRM, and throwing side, all of which could be important factors for throwing shoulder injuries. LEVEL OF EVIDENCE Level III; Cross-Sectional Case-Control Design; Prognosis Study.