Association Between Shoulder Morphological Changes and Glenohumeral Maximum External Rotation During Late Cocking Phase.

BACKGROUND

Excessive external rotation of the glenohumeral joint during the late cocking phase of throwing is a factor in internal impingement; however, the relationship between maximum external rotation (MER) of the glenohumeral joint and morphological changes in the shoulder joint is unclear.

PURPOSE

To clarify whether glenohumeral MER is associated with quantified assessment of morphological changes in the throwing shoulder joint.

STUDY DESIGN

Descriptive laboratory study.

METHODS

This study included 15 male university and adult baseball players from a competitive team. The posterior glenohumeral distance (mm) and area of impingement (mm), reflecting morphological changes in the shoulder joint, were measured using open magnetic resonance imaging. The percent posterior glenohumeral distance (%PGHD) and percent area of impingement (%AOI) were calculated as these values of the throwing shoulder divided by those of the nonthrowing shoulder. With a 3-dimensional motion analysis system, bar markers were affixed to the acromion and humerus, and the glenohumeral MER angle was measured.

RESULTS

Simple linear regression analysis revealed that the glenohumeral MER angle was associated with the %PGHD (β coefficient = 0.685; = .005) and %AOI (β coefficient = 0.754; = .001).

CONCLUSION

The glenohumeral MER angle was associated with the %PGHD and %AOI, which reflects morphological shoulder-joint changes.

CLINICAL RELEVANCE

Assessment of excessive external rotation of the glenohumeral joint during the late cocking phase contributes to the understanding of morphological changes in the shoulder joint and related throwing injuries.