What is it?
The AC (acromioclavicular) joint is a thick fibrous joint that connects the top of the shoulder blade to the outer end of the collarbone. The joint is required to be strong and supportive and is the primary way in which weight-bearing forces are transferred from the arm to the rest of the skeleton. The joint is connected by three strong ligaments, the acromioclavicular, corococlavicular and corocoacromial ligaments.
How does this injury occur?
The primary mechanism that will cause this joint and its ligaments to be injured is a force that separates the shoulder away from the collarbone, usually in a downwards direction. This can occur from a fall into the ground where the top of the shoulder hits the ground first, a rugby tackle or a fall onto an outstretched hand. As with all injuries, there are many variations in severity and a grading system has been developed to classify AC joint injuries.
What are the symptoms?
After an AC joint injury, there is usually immediate pain on the top of the shoulder, often with swelling and bruising. There is usually some loss of movement of the shoulder and pain from putting weight through the arm or carrying heavy objects. In severe cases, there is a visible lump on top of the shoulder known as a ‘step deformity’, where an obvious height difference can be seen between the top of the shoulder and the collar bone. There is frequently pain felt when reaching across the body, such as when putting on a seatbelt.
To confirm the diagnosis, your physiotherapist can perform some clinical tests and sometimes an X-ray can help to grade the severity of the injury. The classification that would be given to you by your physiotherapist or doctor helps to determine the optimal course of action for each injury.
There are different classification systems, some use four grades and the other six. Injuries with a smaller number of ligament fibres being torn are given a lower grade classification, going upwards as further damage is incurred. Injuries classified as higher grades will require surgical repair.
How can physiotherapy help?
The role of physiotherapy in this case is to ensure the joint is supported and given a chance to heal naturally while maintaining strength and movement of the shoulder girdle. This is done initially by providing support to the joint. You may need to have your arm supported in a sling or brace for some of this time, or your physiotherapist can show you some taping techniques to add support.
Most AC joint sprains take around six weeks to fully heal, although some patients report ongoing shoulder problems years later. For this reason, a comprehensive rehabilitation program is very important. More severe sprains or total separations may require surgery to stabilise the joint and treat any associated fractures. Surgical repair will also require a proper rehabilitation program afterwards.