A biomechanical confirmation of the relationship between critical shoulder angle (CSA) and articular joint loading

The critical shoulder angle (CSA) has been shown to be correlated with shoulder disease states. The biomechanical hypothesis to explain this correlation is that the CSA changes the shear and compressive forces on the shoulder. The objective of this study is to test this hypothesis by use of a valida...

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Bibliographic Details
Published in:	Journal of shoulder and elbow surgery Vol. 29; no. 10; pp. 1967 - 1973
Main Authors:	Villatte, Guillaume, van der Kruk, Eline, Bhuta, Asim I., Zumstein, Matthias A., Moor, Beat K., Emery, Roger J.H., Bull, Anthony M.J., Reilly, Peter
Format:	Journal Article
Language:	English
Published:	United States Elsevier Inc 01-10-2020 Elsevier
Subjects:	Adult Biomechanical Phenomena computational shoulder model Computer Simulation Critical shoulder angle (CSA) glenohumeral joint Humans joint wear Kinetics Life Sciences Male Models, Anatomic Movement Range of Motion, Articular rotator cuff Shoulder Joint - physiopathology Stress, Mechanical Young Adult glenohumeral joint Computer Modeling rotator cuff computational shoulder model Critical shoulder angle (CSA) Basic Science Study joint wear
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Summary:	The critical shoulder angle (CSA) has been shown to be correlated with shoulder disease states. The biomechanical hypothesis to explain this correlation is that the CSA changes the shear and compressive forces on the shoulder. The objective of this study is to test this hypothesis by use of a validated computational shoulder model. Specifically, this study assesses the impact on glenohumeral biomechanics of modifying the CSA. An inverse dynamics 3-dimensional musculoskeletal model of the shoulder was used to quantify muscle forces and glenohumeral joint forces. The CSA was changed by altering the attachment point of the middle deltoid into a normal CSA (33°), a reduced CSA of 28°, and an increased CSA of 38°. Subject-specific kinematics of slow and fast speed abduction in the scapular plane and slow and fast forward flexion measured by a 3-dimensional motion capture system were used to quantify joint reaction shear and compressive forces. Increasing the CSA results in increased superior-inferior forces (shearing forces; integrated over the range of motion; P < .05). Reducing CSA results in increased lateromedial (compressive) forces for both the maximum and integrated sum of the forces over the whole motion (P < .01). Changes in the CSA modify glenohumeral joint biomechanics with increasing CSA producing higher shear forces that could contribute to rotator cuff overuse, whereas reducing the CSA results in higher compressive forces that contribute to joint wear.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	1058-2746 1532-6500
DOI:	10.1016/j.jse.2020.03.002