What is AC Joint Separation?

Acromioclavicular (AC) Joint Separations are common injuries that affect the shoulder girdle. Athletes from contact sports are more likely to suffer from AC separations compared with the general population.

The AC joint is where the acromion (a part of the shoulder blade) connects to the clavicle (collar bone) at the top of the shoulder. This joint helps maintain the position of the shoulder and is very important for shoulder control, motion, and strength. The motion of the AC joint is minimal, but it plays a part in normal shoulder function.

What are the signs and symptoms?

AC Joint Separation is characterised by: 

• Pain
• Limited motion in the shoulder
• Swelling
• Bruising
• Tenderness at the top of the shoulder

What are the causes?

The stability of the AC joint is provided by the joint capsule and capsular ligaments, and injury occurs when these structures are damaged. the joint can become unstable and painful, and shoulder function can be affected.

The AC joint is strong, but its location makes it vulnerable to injury from trauma. Injury to the ligaments (also called shoulder separation) can occur as a result of a sudden fall onto the shoulder, or during contact sports when the patient’s arm is adducted, and also can occur from a direct blow or other trauma.

Besides the mechanism of the direct impact, an indirect situation may also be introduced by a fall on the outstretched arm which could transmit the force to the inferior aspect of the acromion through the humeral head, resulting in the AC injuries.

How is it diagnosed?

AC joint Separation can usually be identified during a physical exam. X-rays can sometimes confirm the diagnosis and determine the severity of the injury, but in many people who have a low-grade separated shoulder, early X-rays are often normal. During the physical exam the doctor will look at blood flow, muscle strength, and signs of a broken shoulder or damage to the rotator cuff.

How is it treated?

The options for treatment depend on factors including the severity of separation, the patient’s age, as well as the pre-injury activity level. Treatment decisions should only be made once anatomy, biomechanics, injury pattern, and classification of AC separations are fully understood.

Non-operative treatment can be applied, such as anti-inflammatory medications, hot and cold compresses, and adapting activity. Physical therapy, including passive and active range-of-motion exercises, may begin as soon as the symptoms resolve. Strengthening exercises can be initiated after a full recovery of range of motion of the affected shoulder. Patients’ return to full activity is allowed when a painless active range of motion is fully restored.

If the joint is very unstable, surgical repair may be needed to improve stability, relieve pain, and optimise shoulder function.