AC Joint Injuries
An acromioclavicular joint separation, or AC joint separation, is a very frequent injury among younger, physically active people. The most common cause of an AC joint separation is falling on the shoulder, which results in the clavicle (collar bone) separating from the scapula (shoulder blade).
The shoulder is made up of three bones: the scapula (shoulder blade), the humerus (upper arm bone), and the clavicle (collarbone).The part of the scapula that makes up the top of the shoulder is called the acromion. The AC joint is where the acromion and the clavicle meet.
Ligaments are soft tissue structures that connect bone to bone. The AC ligaments surround and support the AC joint. Together, they form the joint capsule. The joint capsule is a watertight sac that encloses the joint and the fluids that bathe the joint. Two other ligaments, the coracoclavicular ligaments, hold the clavicle down by attaching it to a bony knob on the scapula called the coracoid process.
AC joint separations are graded from mild to severe, depending on which ligaments are sprained or torn.
- Grade 1 injuries are the mildest type of injury. A simple sprain of the AC ligaments would fall under this category.
- Grade 2 AC separations involve a tear of the AC ligaments and a sprain of the coracoclavicular ligaments.
- Grade 3 injuries would involve a complete tear of the AC ligaments and the coracoclavicular ligaments. This injury results in an obvious bump on the shoulder.
Three additional grades of AC joint separation (Grades 4-6) are often seen with high energy trauma and are typically treated with surgery due to the excessive degree of separation between the clavicle and acromion.
Symptoms of AC Joint Separation
Symptoms range from mild tenderness felt over the joint after a ligament sprain to the intense pain of a complete separation. Grade two and three separations can cause a considerable amount of swelling. Bruising may make the skin bluish several days after the injury.
In grade three separations, there will be limited range of motion and you may feel a popping sensation when moving the joint. Grade three separations usually cause a noticeable bump on the shoulder.
Getting a Diagnosis
A physical examination can help our fellowship-trained orthopedic specialists determine if you have acromioclavicular joint separation. Your SROSM physician may also request imaging tests to show an AC joint disruption and determine what type of treatment may be best for you.
Based on your evaluation, your physician will be able to determine the best course of treatment for your AC joint injury. Some AC joint separations can be treated non-surgically, while others may require a surgical procedure.
You can learn more about AC joint injuries by downloading our educational publication A Patient’s Guide to Acromioclavicular Joint Separation.