The Effect of Excessive Glenhumeral Internal Rotation Deficit on Subacromial Joint Space and Forward Scapular Posture among Baseball Pitchers

Abstract

Objectives:Baseball pitchers frequently present with varying levels of glenohumeral internal rotation deficits (GIRD) in their throwing arms when compared to their non-throwing arms. However, excessive bilateral differences in internal rotation motion have been associated with several shoulder pathologies including both subacromial and internal impingement. Additionally, patients diagnosed with subacromial impingement commonly present with decreased subacromial joint space and increased forward scapular posture. These characteristics have not been, as of yet, evaluated and associated to those pitchers who present with excessive GIRD. The purpose of this study was to determine if a group of baseball pitchers with excessive GIRD have differences in subacromial joint space and forward scapular posture when compared to a control group.Methods:Twenty-five asymptomatic professional baseball pitchers with excessive GIRD were matched with 25 pitchers with acceptable levels of GIRD. Excessive GIRD was classified as an amount greater than 10% of the total arc of motion (i.e. dominant shoulder total arc=160°; 0.10x160°=16°; excessive GIRD=>16°). A digital inclinometer was used to measure glenohumeral internal and external rotation range of motion with participants in a supine position and their scapula stabilized. Diagnostic ultrasound was used to measure the distance of the subacromial joint space with the throwing arm resting at the side of the participant’s body (0° abduction). Bilateral forward scapular posture was assessed with each participant standing against a wall and then the distance between the wall and their anterior acromion was measured using the double square technique. The bilateral difference between these measurements was used to determine the amount of forward scapular posture for the throwing arm. Separate t-tests were run to determine significant differences between groups (p<0.05).Results:Results are summarized in Figure 1. The total arc of motion and GIRD for the excessive group was 153.7°±13.4° and -23.5°±5.1°, and 160.5°±16.1° and -3.6°±9.0° for the acceptable level of GIRD group. The excessive GIRD group presented with significantly less subacromial space (9.4mm±2.6 mm) than the control group (11.1mm±2.4 mm) (p=.02). The excessive GIRD group also had significantly more forward scapular posture (10.8mm±11.0 mm) of their throwing arm than the acceptable level of GIRD group (3.9mm±8.8 mm) (p=.01).Conclusion:We found that baseball pitchers with higher levels of GIRD had less subacromial space and more forward scapular posture in their throwing arms compared to pitchers with acceptable levels of GIRD. Our findings suggest that increased GIRD may be a precursor to pathologies associated with decreased subacromial space and forward scapular posture such as subacromial impingement. We suggest that players identified with excessive GIRD perform shoulder strengthening and stretching exercises designed to improve scapular positioning.