The AC (acromioclavicular) joint is the pointy protrusion near the top, outer edge of the shoulder. The AC joint allows you to lift your arm up above your head. Technically speaking, it is the junction of the outside end of the collarbone (clavicle) and the acromion (bony projection) on the top of the shoulder blade (scapula). AC joint injuries are common in younger active individuals. They can range from sprains of the AC and coracoclavicular (CC) ligaments to complete dislocation of the AC joint.  

What are the different types of AC injuries?

Type I and II AC injuries, where the ligament tears are incomplete and the joint is still intact, are treated conservatively. There is a lot of debate on the best way to treat type III injuries. In these injuries, AC and CC ligaments as well as the joint capsule are ruptured, elevating the clavicle. The damage to the AC joint may injure the cartilage within the joint and can later cause arthritis of the joint.


What causes AC joint injuries?

The mechanism of injury to the AC joint can be either direct or indirect. Direct impact can be caused by collision or a fall onto the shoulder with the arm next to the body (ie, in an adducted position). Indirect injuries are less common, but can occur after a fall onto an outstretched arm. In most indirect injuries, the AC ligament is more commonly affected than the CC ligaments. AC joint injuries—the type III injuries—are often seen after falling off or colliding with bicycles, in contact sports and in car accidents.


How do I know if have an AC joint injury?

AC joint injuries are diagnosed based on your medical history as well as by a physical examination. Your physiotherapist looks for a ‘step’ deformity of the joint, any swelling or bruising, and feels for any tenderness over the AC joint and outer edge of the collarbone. Range of motion of the shoulder will be limited because of pain. To test for an AC joint injury, your physiotherapist will lift your arm up to 90o and take it passively across your chest with the elbow flexed (cross arm adduction). If the AC joint is injured, this test will cause pain. You may also be sent for an X-ray to see how severe the injury is.

Curiously, Stage I AC sprains are more painful in the short term than the more serious Stage III. This is because the total tearing of the ligaments (Stage III) removes all loading from them, whereas the partially torn ligaments of a Stage I injury are stressed by any movement of the shoulder blade (and arm).


How can physiotherapy help with AC joint injuries?

In the early stage after injury, your physiotherapist can tape your AC joint and/or apply a sling so your forearm is supported. You will need to use a sling for 3–4 weeks, particularly if your arm is hanging for long periods of time, but this will depend on your symptoms. If your pain has significantly decreased and your function has improved, you may only need a sling for a week, particularly if you have a type I AC joint sprain.

You will need to support your arm while you are sleeping and, to begin with, you may prefer to sleep propped up in a recliner chair. You may find initially that ice is helpful in decreasing the swelling and bruising.

One to two weeks after the injury, your physiotherapist may suggest you do gentle swinging exercises for your shoulder below 90o (pendular exercises), as well as gentle scapular setting exercises. After 4–6 weeks, your physiotherapist may gently mobilise your shoulder joint (glenohumeral joint) and collarbone (distal clavicle) to prevent excessive scarring and improve joint mobility.

Once full range is achieved within a pain-free state, you will be given progressive resistive exercises (isometrics, isokinetic exercises and sport/activity-specific exercises). Initially the exercises will be closed chain exercises, meaning that your hand remains in contact with a stationary surface, before progressing to open chain exercises where the hand is free in space. You will find that the closed chain exercises are easy to begin with, as they unload the weight of your arm, which means you can do more exercise without provoking pain.


How effective is physiotherapy for AC injuries?

Physiotherapy is effective for managing type I and type II AC joint injuries, according to two 2014 scientific reviews. It is also effective for managing type III injuries, with studies showing that the rehabilitation time is shorter and just as effective as surgery, although the cosmetic outcome is worse. Surgery for AC dislocation can reduce the deformity, but this treatment has more complications and could in fact compromise the function of the shoulder. More severe grades of AC dislocation (types IV-VI) are treated more effectively with surgery.


What can I do at home?

With an AC joint injury you must rest until the structures are healed. You won’t be able to drive your car and you must avoid activities where you are lifting your arm across your body or lifting your arm past 90o. You can do exercises to strengthen your legs and your core, but only if you don’t stress your shoulder. This means sit-ups should be avoided. To maintain your fitness, you can ride a stationary exercise bike.


How long until I feel better?

Activity can be limited for more than six months, particularly with type III injuries. Although AC joint injuries treated without surgery do heal, it is important to note that there is the potential for residual pain, inflammation and possible long-term degenerative changes. Some individuals still feel AC joint symptoms up to 10 years after their injury.