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Updated: Sep 19, 2025
Measuring 3D In-vivo Shoulder Kinematics using Biplanar Videoradiography
Published on: March 12, 2021
Association Between Shoulder Morphological Changes and Glenohumeral Maximum External Rotation During Late Cocking
Makoto Takahashi1,2, Hirotaka Mutsuzaki3,4, Koji Iwamoto5
1Department of Physical Therapy, School of Health Sciences, Japan University of Health Sciences, Saitama, Japan.
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 (mm2), 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; P = .005) and %AOI (β coefficient = 0.754; P = .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.
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