AC Joint Separation
A shoulder separation is an injury to the acromioclavicular (AC) joint on the top of the shoulder. A shoulder separation occurs where the clavicle and the top of the scapula (acromion) come together. AC separation results in moderate to severe pain at the site of the injury, swelling, inflammation, and deformity at the joint. A loss of function, due to the pain and instability, often occurs with high grade separations.
The two most common causes of a shoulder separation are either a direct blow to the shoulder (often seen in football, rugby, or hockey), or a fall on to an outstretched hand (commonly seen after falling off a bicycle or horse). These forces injure the ligaments that surround and stabilize the AC joint. If the force is severe enough, the ligaments attaching to the underside of the clavicle are torn. This causes the “separation” of the clavicle from the scapula. In the case of torn ligaments, surgical repair may be required. In less severe cases, or following surgical repair, the shoulder muscles need to be specifically strengthened so that they can help to prevent future separation.
An AC joint separation injury can range from mild to severe:
- Grade 1 – A mild shoulder separation involves a sprain of the AC ligament that does not move the collarbone and looks normal on X-rays.
- Grade 2 – A more serious injury tears the AC ligament and sprains or slightly tears the coracoclavicular (CC) ligament, putting the collarbone out of alignment to some extent.
- Grade 3 – The most severe shoulder separation completely tears both the AC and CC ligaments and puts the AC joint noticeably out of position.