Acromioclavicular joint injury is one of the common shoulder injuries among physically active people, representing upto 9% of all shoulder injuries. AC joint separation occurs when clavicle (collar bone) separates from the scapula (shoulder blade), commonly due to a fall directly on the “point” of the shoulder or a direct blow to the shoulder, especially in physically demanding sports. A good portion of AC joint injuries occur in people in their twenties and it is found that AC joint injuries are five times common in men than in women. Younger people participating in contact sports are more vulnerable to AC joint injuries. There is a high chance of AC joint separation in sports like hockey, rugby and skiing. Footballers and cyclists who fall over the handlebars can also suffer from AC joint separation. The most common mechanism of injury is by direct contact applied directly over the superolateral border of the shoulder while the humerus is in the adducted position.
Acromioclavicular joint sprains have been classified according to the severity of injury to the acromioclavicular and coracoclavicular ligaments, the acromioclavicular joint capsule, and the supporting muscles of the shoulder (trapezius and deltoid) that attach to the clavicle. Classification is based on AC injury, beginning with trauma to the AC ligaments, continuing to the coracoclavicular ligaments, and finally disrupting the deltotrapezial fascia. Degree of the injury is determined in accordance with the severity of injury sustained by the capsular and extracapsular ligaments and supporting musculature.