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AC Joint Dislocation
Acromioclavicular Joint Dislocation
The AC joint is the only bony connection of your shoulder blade and it is important for maintaining normal dynamics in your shoulder. The AC joint relies on three main structures for stability: Your AC joint capsule, the coraco-clavicular ligaments and the delto-trapezial fascia. These structures are illustrated below. With direct force, normally a fall onto the tip of the shoulder, the joint can be injured and become painful and unstable. In some cases this pain and/or instability requires surgery. The x-ray below shows a high-grade dislocation of the AC joint.
What are the Symptoms of an AC joint injury?
You will likely recall a specific injury – e.g. fall off a bike/rugby tackle. There will be acute pain and swelling over the top of your shoulder and you may notice a step (dislocation of AC joint). Initially you will have reduced function due to pain, but this often settles over the first couple of weeks. However, it may continue and limit your shoulder function and dynamics.
Who gets AC joint injuries?
This is typically an injury that occurs in 18-45 year olds; it is much more common in men and is particularly common in collision sports, such as rugby. Other sports with risk of falling onto the shoulder, such as cycling, skiing and riding are also higher risk.
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What do the 'grades' of injury mean?
Different grades of injury can occur, ranging from a capsular sprain of the AC joint, through to rupture of all stabilizers and gross displacement of the AC joint. The grade of injury does not necessarily predict the functional impairment you will experience. It is possible for low grade sprains to cause on-going issues, while patients with obvious deformity can sometimes suffer few symptoms. There spectrum of injury has been divided into 6 grades. This grade is determined by x-rays and clinical examination. It can help us understand which structures have been damaged.
Grades 1 and 2 – you will not have a significant step and your AC joint will be stable. Your joint capsule has been injured, but your important coraco-clavicular ligaments will be intact. 90% will recover without surgery. 10% will develop ongoing pain that may require treatment.
Grade 3 – you will have a step over your shoulder. On x-ray your collarbone will have moved out of its socket by approximately 100%. Your coraco-clavicular ligaments have been injured, but it is probable that your delto-trapezial fascia remains intact. Repeated studies suggest that most (85%) of patients do well without surgery and a recent review confirmed no obvious superiority of early fixation for these injuries. If you are coping well at 10 days or so after injury, it is best not to have an operation. If you are still struggling at this point then you may decide that surgery is indicated.
Grade 4 – as for Grade 3, but your collarbone is unstable posteriorly. This causes the collarbone to penetrate the trapezius muscle behind the AC joint as you move your arm across your body. Patients are normally very sore and limited by this and most will opt for early surgery.
Grade 5 – In this case, the overlying delto-trapezial fascia has also ruptured and the collarbone has displaced yet further from it’s original position. Most surgeons would offer early surgery to restore stability in this group.
Grade 6 – An extremely rare injury pattern where the collarbone comes to rest beneath the coracoid process.
What non-surgical treatments are there?
Rest, activity modification, painkillers and anti-inflammatories are the first step, as for many injuries. Physiotherapy helps to reduce swelling, restore range of motion and muscle control to your shoulder.
Intra-articular (Cortisone) Steroid Injection can be helpful if symptoms persist in low grade sprains, but they are not indicated if you have significant deformity.