The acromioclavicular, or AC joint, is a joint in the shoulder where two bones meet. One of these bones is the collarbone, or clavicle. The second bone is actually part of the shoulder blade (scapula), which is the big bone behind the shoulder that also forms part of the shoulder joint. The portion of the shoulder blade that meets the clavicle is called the acromion. As a result, where the clavicle meets the acromion is called the AC joint.
Stability of the AC joint is provided by a number of structures, including the joint capsule and ligaments.
How do I injury my AC joint?
The AC joint is a common site of injury in athletes who fall onto the point of their shoulder or with an outstretched arm.
What are the symptoms of an AC joint injury?
Symptoms include pain, limited motion of the shoulder (especially across your body), swelling, bruising and tenderness at the top of the shoulder. You may also notice that the collarbone is sitting higher or notice a bump at the top of the shoulder.
Types of AC joint injuries:
The type of shoulder separation depends on how much you tear the AC joint or coracoclavicular (CC) ligaments that hold the joint in place.
Type I = the AC ligament is slightly torn, but there's no damage to the CC ligament is unharmed.
Type II = the AC ligament is completely torn, and there's little or no tear to the CC ligament.
Type III = both the AC and CC ligaments are completely torn. In this case, the collarbone separates from the end of the shoulder blade.
Three more types of AC joint injury are also possible, but rare. These involve tearing of the ligaments and surrounding muscle tissue.
How can Physiotherapy help?
Initially ice is applied to minimise the degree of damage and the injured part is immobilised in a sling for pain relief. This may be for 2-3 days in the case of Type 1 injuries, or up to 6 weeks in Type 2 or 3 injuries. Strengthening exercises will be commenced once your pain is under control. Return to sport is possible when there is no further localised tenderness, full range of pain-free movement, sport-specific strength, and general cardiovascular fitness.
