Understanding Acromioclavicular Joint Separation
Your acromioclavicular joint is located where your collarbone and shoulder blade meet. Acromioclavicular joint separation is an injury that occurs when a force to your shoulder pulls these bones apart. It’s more commonly known as shoulder separation.
Acromioclavicular (AC) joint separation is very common. It’s estimated to make up about 4% to 12% of shoulder injuries and occurs in about 3 to 4 people per 100,000 every year. People who participate in contact sports like ice hockey or American football are particularly at risk of AC joint injuries.
Low-grade AC joint separation can often be treated conservatively with a sling or harness to rest your injured shoulder. Severe injuries may require surgical repair of the ligaments and other tissue around the joint.
Read on to learn more about AC joint separation, including symptoms, how it’s managed, and treatment options.
Your AC joint is where a part of your shoulder blade called the acromion process attaches to your collarbone. You may be able to feel this joint as a notch in the front of your shoulder at the end of your collarbone.
Your AC joint is held together by a strong piece of connective tissue called the AC ligament. Other ligaments such as the coracoclavicular ligament also support this joint.
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AC joint separation occurs when a sudden force to your shoulder pulls your shoulder blade and collarbone apart and damages the ligaments. The most common cause of AC joint separation is a sudden direct trauma to your shoulder, such as during a fall or collision.
Types of AC joint separation
Medical professions subdivide AC joint separation into different types depending on the severity of the injury. The Rockwood system , developed in the 1980s, is the most common classification system. It divides AC joint separation into six categories.
| Description | |
|---|---|
| Type I | sprain of the AC ligament |
| Type II | rupture of AC ligament without damage to coracoclavicular (CC) ligament |
| Type III | complete rupture of AC and CC ligaments but no injury to the surrounding fascia (collarbone is displaced less than its width) |
| Type IV | outer part of your collarbone is displaced backward (a complete rupture of your AC ligaments and a partial rupture of the CC ligaments) |
| Type V | complete rupture of AC and CC ligaments and a rupture in your surrounding fascia (outer part of your collarbone is raised more than its width) |
| Type VI | lateral part of your collarbone is below one or both parts of your shoulder blade, called the acromion and coracoid processes |
