A shoulder separation is actually an injury involving the AC (acromioclavicular) joint. This joint is where the clavicle connects with the highest point of the shoulder blade (acromion).
Typically this injury occurs due to a hard fall onto the shoulder and upper extremity, causing damage to the ligaments that stabilize and surround the AC joint. The separation occurs when enough force has been applied to tear the ligaments, causing the clavicle to separate from the acromion, which then moves downward with the weight of the arm. Separations injuries range in severity from a sprain to the ligament or a complete tear, in which surgical intervention is typically required.
Deformation around the end of the clavicle, which will appear as a bulge due to the separation of the acromion and the downward shift of this bone, is the most noticeable symptom of this injury.
Immobilization, to allow the ligaments of the joint to adequately heal, is the most common treatment. The deformation caused by the separation may never return to normal, however. In severe cases, surgical intervention followed by physical therapy may be required in order to strengthen the ligaments of the AC joint and restore range of motion and stability.