Relationship Between Shoulder External Rotation and Glenohumeral Joint Alignment Changes in Baseball Players

Area of Science:

• Orthopedics
• Sports Medicine
• Biomechanics

Background:

• Throwing injuries are common in athletes.
• Understanding glenohumeral joint mechanics is crucial for injury prevention.

Purpose of the Study:

• To investigate the effect of shoulder external rotation on humeral head alignment.
• To determine the relationship between humeral head translation and posterior glenohumeral distance.

Main Methods:

• Magnetic resonance imaging (MRI) was used to measure humeral head translation and posterior glenohumeral distance.
• Measurements were taken on 28 baseball players' throwing shoulders at various external rotation angles (90°, 100°, 110°).

Main Results:

• Posterior translation of the humeral head significantly increased at 110° external rotation compared to 90° (P = .003).
• Humeral head translation correlated with posterior glenohumeral distance at 90° and 100° external rotation.

Conclusions:

• Greater shoulder external rotation leads to increased posterior humeral head translation and proximity to the posterior glenoid rim.
• These biomechanical changes during the late cocking phase may contribute to throwing shoulder injuries.