High School Baseball Pitchers Demonstrate Side-to-Side Symmetry in Glenohumeral Joint Laxity and Stiffness
Sauers EL, Crawford SD. Department of Sports Health Care, Arizona School of Health Sciences, Mesa, AZ

Introduction: Repetitive pitching has been theorized to result in anterior capsular attenuation and posterior capsular contracture in the throwing shoulder.  These adaptations have been linked to shoulder impairment.

Purpose: The purpose of this study was to compare glenohumeral joint laxity and stiffness between the throwing and non-throwing shoulders of high school baseball pitchers.  

Subjects and Design: A descriptive design was utilized to compare glenohumeral joint laxity and stiffness between the throwing and non-throwing shoulders of twenty-two high school baseball pitchers (age =16.5 ± .74 yrs, height 178.51 ± 7.66 cm, mass 75.43 ± 13.24 kg).

Methods: Measures of glenohumeral joint laxity and stiffness were obtained using a commercially available computerized-stress device (LigMaster, Sports Tech., Charlottesville , VA ).  Anterior glenohumeral joint laxity and stiffness measurements were taken with the shoulder in 90º of abduction and both neutral rotation and in 90º of external rotation.  Posterior glenohumeral joint laxity and stiffness measurements were obtained with the shoulder in 90º of abduction and neutral rotation.  Glenohumeral joint laxity and stiffness were evaluated using two separate repeated measures ANOVAs with 2 within-subjects variables:  side (throwing and non-throwing), and shoulder displacement position (anterior in neutral rotation, posterior in neutral rotation, and anterior at 90° of external rotation). 

Results: No significant differences were found for glenohumeral laxity (p = .338) between sides.  However, a statistically significant main effect for position was present (p < .0001).  Tukey’s post hoc analysis revealed that glenohumeral joint laxity was significantly lower in the anterior at 90° of external rotation position compared to the anterior at neutral rotation and posterior at neutral rotation positions.  A significant difference was observed for glenohumeral joint stiffness between sides (p = .049), but the difference was extremely small (< 1 N/mm).  A significant main effect for position was present (p < .0001) and Tukey’s post hoc analysis revealed that glenohumeral joint stiffness was significantly greater in the anterior at 90° of external rotation position compared to the anterior at neutral rotation and posterior at neutral rotation positions.  The side x position interactions were not significant for either glenohumeral joint laxity (.325) or stiffness (p = .162).  No significant difference between sides was observed for total anterior-posterior laxity in neutral rotation (p = .626). 

Conclusions:  These results demonstrate that glenohumeral joint laxity decreases and stiffness increases in the functional throwing position of 90º of abduction and 90º of external rotation. There were no clinically significant side-to-side or directional differences in laxity and stiffness.

Clinical Implications: The healthy throwing shoulder should not exhibit side-to-side or directional asymmetry in glenohumeral joint laxity and stiffness.