Correlation of glenohumeral internal rotation deficit with shear wave ultrasound elastography findings for the posterior inferior shoulder capsule in college baseball players

Background: The glenohumeral internal rotation deficit (GIRD), primarily caused by the tightness of the posterior capsule, is a major risk factor for shoulder injuries in overhead throwing athletes. Quantitative evaluation of posterior capsular thickness and tightness can help determine the relationship between the posterior inferior capsule and GIRD. One previous study has assessed posterior capsule tightness using shear wave elastography (SWE), in college baseball players; however, it did not address the cutoff value of capsular elasticity that could be considered as abnormal capsular tightness. We aimed to re-evaluate effectiveness of SWE in quantifying posterior shoulder capsule tightness in college baseball players and determine the cutoff value of abnormal capsular elasticity that can predict impending throwing-related shoulder injuries associated with GIRD. Methods: Twenty-four college baseball players were enrolled in this study. External and internal rotation of the shoulder joint was assessed. The participants were classified into the GIRD group if their throwing shoulder showed >20° of internal rotation loss compared with their nonthrowing shoulder. In a longitudinal ultrasonographic scan of the posterior inferior capsule, shear wave (SW) velocity and thickness were measured at the point nearest to the labrum on both shoulders. Results: Of the 24 subjects, 6 had a GIRD. The mean value of the SW velocity in the throwing shoulder was greater in the GIRD group than in the non-GIRD group (P = .006). The SW velocity difference between the throwing and nonthrowing shoulder was also greater in the GIRD group than in the non-GIRD group (P < .001). There was no significant difference in the thickness of the posterior inferior capsule between both groups. In correlation analysis, the difference in the SW velocity was more strongly correlated with the GIRD than with the SW velocity in the throwing shoulder. When we assume that a 20° GIRD is indicative of a shoulder at risk, the cutoff SW velocity in the throwing shoulder is 4.81 m/s and the SW velocity difference is 0.77 m/s. Conclusion: The SW velocity is closely associated with posterior shoulder capsular tightness and may be of quantitative value in baseball players.