Lennard Funk & Catherine Sulzmann, 2019
The movement of the AC joint is a combination of translation and rotation in a 3D plane. This movement has been described as a relative motion of the scapula to the clavicle around a screw axis passing through the insertions of both the acromioclavicular and the coracoclavicular ligaments on the coracoid process [Sahara et al, 2006].
This screw axis describes the total rotation and translation, with a total of 35 degrees of rotation with full shoulder abduction. This suggests that the acromioclavicular joint allows significant motion between the scapula and clavicle.
In the interactive model below we have demonstrated the relative motion of the scapula to the clavicle around the screw axis from 0 degrees of abduction to maximum abduction.
(Note that although we have shown the clavicle as fixed in position, that is not the case - the clavicle moves from the sternoclavicular joint relative to the sternum and trunk)