The AC joint is located at the top of your shoulder where the collarbone and shoulder blade meet. It is vulnerable to injury during certain types of high impact sports or as the result of a heavy fall into the shoulder. The AC joint may also develop overuse injuries and over time this may lead to osteoarthritis and osteolysis (a stress fracture at the lateral end of the clavicle usually related to weightlifting).
What is the AC joint?
The acromioclavicular (AC) joint is the part of your shoulder where the clavicle (collarbone) and acromion (part of the shoulder blade or scapula) meet. In between the two bones within the AC joint is a flexible cartilage disk, which covers and protects the ends of the bones, allowing them to slide smoothly over each other without rubbing. The AC joint helps to maintain the position of the shoulder and plays an important role in shoulder movement and control. The joint capsule and ligaments help to stabilise the AC joint.
Common AC joint injuries
Between 40% and 50% of all acute shoulder injuries in contact sports involve damage to the AC joint. Injuries to the AC joint are often graded from type 1 to type 6, with type 1-2 being the least serious (a sprain) and type 3-6 being more severe, (complete dislocation of the distal clavicle). This method of grading AC joint injuries on an xray is probably now a little outdated as it doesn’t correlate well with the speed of recovery or need for surgery, but it is still very important to do xrays to diagnose the injury in the first place.
AC joint sprain or separation: This type of injury is normally the result of a sudden fall onto the shoulder, resulting in injury to the capsule and ligaments of the AC joint. Symptoms include shoulder instability, pain and loss of function.
AC joint arthritis: This normally develops over time as the result of wear and tear of the AC joint due to overuse. It is common in labourers and weightlifters. It is often first brought to the patient’s attention after a minor injury.
Symptoms of AC joint injuries
The most common symptoms of AC joint injuries are pain and tenderness at the top of the shoulder above the AC joint. There may be swelling around the joint or a noticeable bump. Pain when lifting the arm to the side or across the front of the body and loss of movement in the shoulder are also common symptoms.
Who is at risk?
Sports men and women – particularly those involved in contact sports – are at risk of AC joint injury. It is also common among weightlifters and sports with a high risk of falling (such as skiing or ice skating). Labourers who work in physically demanding jobs, particularly those with repeated overhead movements, are especially prone to AC joint arthritis and men are five times more likely than women to injure their AC joint. Men in their 20s and 30s are at greatest risk of AC joint injuries.
Diagnosing AC joint injuries
If you fall heavily onto your shoulder and experience pain and loss of movement, or if your AC joint is swollen or there is a noticeable bump you should seek medical advice. Initially, if the symptoms are mild, you can try resting your shoulder and using ice packs to reduce inflammation and taking anti-inflammatories. However, if this fails to relieve the symptoms, it’s important to get a proper diagnosis.
You will be given an X-ray to make the diagnosis and help grade the severity of the injury. This can also show up any osteoarthritis or osteolysis. The most important part of the assessment is strength of your shoulder blade muscles and postion of your shoulder blade. This cannot be done on an xray and requires a specialist to examine you.
Treating AC joint injuries
Most AC joint injuries can be treated with a combination of rest, physiotherapy, anti-inflammatories and a gradual return to full activity. Some people are much more reliant than others on their collarbone to hold the should blade in the correct position. Doctors are not completely sure why this is so but is most likely related to the shape of the spine, shoulder blade muscle strength and posture. Some babies are born without collar bones but their shoulders move completely normally throughout life! If the injury does not compromise the control of the shoulder blade, no matter how severe it appears on xray, then surgery is not recommended.
If the position of your shoulder blade is compromised after an AC injury, then surgery may be needed. Fixation of the distal end of the clavicle can restore anatomical alignment and allow rehabilitation of your shoulder.. It is best if surgery is performed within the first few weeks of injury as this allows your ligaments to heal naturally. If surgery is delayed then synthetic or donated ligament is often needed to allow stabilisation of the joint.
For patients with AC joint arthritis or osteolysis a steroid injection into the joint can be very helpful and provide longlasting pain relief. If this does not work then an operation to increase the space in the joint is usually recommended. This can be done either with keyhole or traditional open surgery, the latter often having better results in men with larger bones.
If you have experienced an AC joint injury or are experiencing symptoms that could indicate AC joint arthritis or osteolysis, contact us for advice on diagnosis and treatment options.
How we help
Orthopaedic surgeons will always tailor-make treatments to the needs of individual patients and will discuss all of the treatment options with you fully so you can reach a shared decision about the best way forward.
If you are experiencing shoulder pain or a loss of function in your shoulder joint, contact us to discuss your diagnosis and treatment options