Acromioclavicular (AC) Separation
Acromioclavicular (AC) separation, commonly referred to as shoulder separation, does not involve injury to the shoulder joint. The injury instead involves various degrees of dissociation between the wingbone (acromion) and the collarbone (clavicle.) The most common mechanism of injury involves a fall directly onto the shoulder, with injury to the ligaments that surround and stabilize the AC joint. In the case of an extremely high energy fall, the ligaments attaching to the inferior aspect of the clavicle are torn, causing the "separation" of the clavicle and acromion. The acromion and scapula actually moves downward from the weight of the arm, creating a "bump" or bulge above the shoulder.