Scapular angular positioning at end range internal rotation in cases of glenohumeral internal rotation deficit

Study Design: Controlled laboratory study. Objectives: Investigate the relationship between glenohumeral internal rotation range-of-motion deficit and 3-dimensional scapular angular positioning during active arm movements in participants with recent participation in overhead sports activity. Background: Subacromial impingement is one of the most common shoulder pathologies and is multifactorial in etiology. Posterior glenohumeral joint capsule tightness has been theorized to contribute to one potential causal factor: abnormal scapular positioning. Methods and Measures: Twenty-three subjects, who had participated in competitive sports involving overhead activity within the last 5 years, were categorized into 2 groups based on the degree of glenohumeral internal rotation deficit (20% deficit threshold). Scapular angular positioning of subjects performing shoulder internal rotation from 90 degrees flexion and abduction shoulder positions was evaluated using 3-dimensional electromagnetic surface tracking. Additional sensors monitored trunk and humeral motion. Scapular position data at end range glenohumeral internal rotation, along with glenohumeral internal rotation range of motion measurements, were used to analyze the relationship between glenohumeral internal rotation deficit and scapular position using 2-way ANOVA and regression analyses. Results: The internal rotation deficit group had significantly greater scapular anterior tilt (9.2 degrees difference, P =.04) across positions, as compared to the control group. Regression analysis demonstrated a significant association between glenohumeral internal rotation deficit and scapular position (tilting) during flexed internal rotation (r(2) = 0.37, P =.03) and for scapular position (anterior tilting and upward rotation) during abducted internal rotation (r(2) = 0.35, P =.036). Conclusions: These findings demonstrate a significant relationship between glenohumeral internal rotation deficit and abnormal scapular positioning, particularly increased anterior tilt. This relationship identifies a possible mechanism for development of excessive scapular anterior tilt.