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Posted: February 12, 2021
What is the AC joint?
The AC joint is a plane synovial joint formed between the acromion of the scapula (shoulder blade) and the distal end of the clavicle (collarbone), on top of the shoulder.
The joint is stabilised by the acromioclavicular (AC) ligaments, coracoclavicular (CC) ligaments and the coracoacromial (CA) ligament (Kiel & Kaiser, 2020). This joint is small but contributes to achieving full shoulder range of motion.
AC injuries are common in sports such as football, rugby league and rugby union. They may account for up to 40% of all shoulder injuries and nearly 10% of all injuries in collision sports (Kiel & Kaiser, 2020).
Mechanism of injury
The AC joint is often damaged by a fall onto the point of the shoulder, or a direct blow to the shoulder (ie a hip and shoulder bump in footy). This compresses the AC joint and can damage the ligaments which stabilise the joint (Brukner & Khan, 2017).
Diagnosis is made on a number of features:
Grades of AC joint injury – grading is based on the Rockwood classification system (see photo below)
It is important to see a healthcare professional to rule out other possible injuries. Some other key things to rule out in an acute shoulder injury include:
Rehabilitation timeframes will depend on the severity of the AC joint injury. All injuries will progress through a series of phases which will involve:
Brukner, P., & Khan, K. (2017). Clinical Sports Medicine. Elsevier.
Kiel, J., & Kaiser, K. (2020). Acromioclavicular Joint Injury. StatPearls.