In silico modeling of glenohumeral joint variation in biomechanical function and stability

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Conference Proceeding

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Publication Title

American Journal of Physical Anthropology


During human evolution, scapular morphology has shifted from a cranial to a more laterally- facing glenoid, presumably facilitating a shift in activities from climbing and hanging to throwing and digging. We utilized three-dimensional bone surface data and kinematics acquired from biplanar videoradiography to build a muscle fiber elongation model and estimate the relationship between cranial orientation of the glenoid and biomechanical function in humans. We hypothesized that at low ranges of abduction (below the head), the lines of action of the muscle fibers would move from perpendicular to the glenoid surface to parallel and the moment arms would decrease as cranial orientation increased. This prediction was based on the reasoning that the joint optimally functions when opposing muscles act to increase the contact force vector, which increases congruence, without supplying a tangent dislocating force. Our results indicate that the cranial orientation of the glenoid substantially alters the lines of action of inferiorly directed muscles. We find that in individuals with more cranially oriented glenoid, the teres major, teres minor, and infraspinatus have less ability to translate the humerus inferiorly. This may increase the risk of rotator cuff dysfunction by compromising the ability of these muscles to maintain a stable shoulder. However, it also remains possible that this reduced translation ability in cranially oriented glenoids acts instead to prevent excessive translation, yielding a more stable joint. Further modeling study of glenohumeral joint dynamics is required to parse these alternatives





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