• An acromioclavicular joint separation, or AC separation, is an injury where the clavicle (collar bone) separates from the scapula (shoulder blade).
• AC separation is caused by a fall directly on the edge of the shoulder or a direct blow received in a contact sport.
• Football, soccer, and hockey players as well as cyclists most commonly sustain AC separations.
• The severity of an AC separation depends on the extent of ligament damage

Grade I – Slight displacement at AC joint. The acromioclavicular ligament is stretched. This is the most common type of injury to the AC joint.

Grade II – A partial dislocation of the AC joint. The acromioclavicular ligament is completely torn, while the coracoclavicular ligaments remain intact.

Grade III – A complete AC separation. The acromioclavicular ligament and the coracoclavicular ligaments are fully torn. The shoulder has an obvious acromioclavicular ligament which is completely torn, while the coracoclavicular ligaments remain intact.

Grade V – A complete separation of the AC joint with disruption of deltoid and trapezial muscle fascia. This severe separation demonstrates the most obvious visual bump on the shoulder.