One Hatfield
Pinehill Hospital
Spire Harpenden

Acromioclavicular Joint Separation

What is it?

An acromioclavicular joint separation is a fairly common injury after an impact to the shoulder, especially in certain sports such as rugby. A separation occurs when the structures making up the AC joint are disrupted, allowing excessive movement of the bones on either side.

What is the AC joint?

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 hold these two bones together. 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.

What causes it?

The most common cause of an AC joint separation is falling on the shoulder. As the shoulder strikes the ground, the force from the fall pushes the scapula down. The collarbone, because it is attached to the rib cage, cannot move enough to follow the motion of the scapula. Something has to give. The result is that the ligaments around the AC joint begin to tear, separating (dislocating) the joint.

AC joint separations are graded from mild to severe, depending on which ligaments are sprained or torn. The mildest type of injury is a simple sprain of the AC ligaments. Doctors call this a grade 1 injury. A grade 2 AC separation involves a tear of the AC ligaments and a sprain of the coracoclavicular ligaments. A complete tear of the AC ligaments and the coracoclavicular ligaments is a grade 3 AC separation. This injury results in the obvious bump on the shoulder. Grade 4 – 6 describe severely displaced injuries.

What are the symptoms?

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, you may feel a popping sensation due to shifting of the loose joint. Grade three separations usually cause a noticeable bump on the shoulder.

How is it diagnosed?

Your doctor will need to get information about your injury and a detailed medical history. You will need to answer questions about past injuries to your shoulder. You may be asked to rate your pain on a scale of one to 10. Diagnosis is usually made by the physical examination. Your doctor may move and feel your sore joint. This may hurt, but it is very important that your doctor understand exactly where your joint hurts and what movements cause you pain. Your doctor may order X-rays. X-rays can show an AC joint disruption, and they may be necessary to rule out a fracture of the clavicle. In some cases, X-rays are taken while holding a weight in each hand to stress the joint and show how unstable it is.

What is the treatment?

Nonsurgical Treatment:
Treatment for a grade one or grade two separation usually consists of pain medications and a short period of rest using a shoulder sling. Your rehabilitation program may then be directed by a physiotherapist. Range-of-motion exercises are started as pain eases, followed by a program of strengthening, including strength exercises for the rotator cuff and shoulder blade muscles. In most cases, the pain goes away almost completely within three weeks. Full recovery can take up to six weeks for grade two separations and up to 12 weeks for grade three separations. Since there is little danger of making the condition worse, you can usually do whatever activities you can tolerate.

The treatment of grade three AC separations is somewhat controversial. Many studies show no difference whether a person is treated with surgery or conservative treatment. Even with surgery, a bump may still be present where the separation occurred. And a significant portion of people who undergo surgery will need another operation later. Several studies have looked at what happens to the AC joint after this injury. It appears that many people, whether they had the joint repaired surgically or not, will need an operation at some time in the future. The injured joint degenerates faster than normal. Over time it becomes arthritic and painful. This process may take years to develop, but sometimes it happens within one or two years.

Surgical treatment:
Some surgeons prefer to repair severe grade three AC separations, especially in high-level athletes, and most grade 4 – 6 injuries. The surgeon starts by putting the joint into its correct position. A variety of implants are available to connect the clavicle back to the coracoid and hold it in place while the ligaments heal. If the injury is fresh, some of these can be inserted using arthroscopic ("keyhole") surgery. This is less painful and allows for a quicker recovery.