Acromioclavicular joint pain (ACJ)
The acromioclavicular joint (ACJ) is found on the roof of the shoulder. The joint is formed medially by the collarbone and laterally by the acromion. It can be acutely injured through trauma to the roof of the shoulder or chronically over time due to wear and tear.
Acute injuries to the ACJ involve varying degrees of damage to the joint capsule and ligaments that give it its stability. These range from sprains that do not affect the joint alignment all the way to complete ligamentous ruptures that can cause complete superior migration of the distal clavicle, sometimes referred to a ‘step deformity’. This can affect shoulder function, especially in young, active, high-demand patients.
The ACJ is also very often a site of arthrosis. With lots of the patients over the age of 40 showing degenerative features at this articulation. It is important to remember, however, that this may or may not be related to symptoms.
Finally, a further condition that can affect this joint is a condition called ‘osteolysis’. It is typically seen in younger, high-demand patients such as those involved in sports and regular gym-goers but is also seen in patients with heavy overhead work such as builders and plasterers. This condition is essentially a stress fracture of the outer end of the clavicle. It is through excessive activities that load the outer clavicle and ACJ, leading to repetitive damage which exceeds the ability of the bone to heal and subsequent bony erosions.
What are the sign and symptoms?
Patients typically present with superior shoulder pain. Unlike other shoulder conditions, patients can usually pinpoint symptoms very well when the ACJ becomes symptomatic. The pain is localised to the joint; they typically have pain with reaching across their body or pain at the very end ranges of shoulder elevation. Their shoulder should not be stiff or weak unless there is concurrent pathology in the shoulder. In traumatic cases, the distal end of the clavicle can be superiorly migrated, showing an obvious deformity at the joint.
How ACJ pain diagnosed?
The clinical symptoms will often be present as discussed previously. If it is decided the ACJ is the likely cause, an X-ray will be helpful to confirm the diagnosis and the extent of any joint pathology, be that traumatic or atraumatic. Ultrasound and MRI can both be helpful as well but are often not required in the initial workup unless there is suspicion of concurrent pathology in the rotator cuff or inside the shoulder joint.
It is important to remember that ACJ arthrosis is very prevalent on plain film x-rays; lots of the time this is not related to the patients’ symptoms. Isolated ACJ pain is relatively rare over the age of 60.
How is ACJ pain treated?
Atraumatic cases of ACJ pain are usually due to arthrosis or osteolysis. Sometimes symptoms can settle without any formal intervention, and all that is required is a short period of activity modification +/- a short course of NSAIDs or analgesia. If things do not settle, then you have treatment options.
- Injection of local anaesthetic and steroid.
This will typically be done under ultrasound guidance to confirm needle placement to make sure the medication is injected directly into the ACJ. This is very effective at reducing any associated inflammation and pain and sometimes is all that is required to break the pain cycle that the patient is in, settling their symptoms long-term. It will also allow better compliance with some physiotherapy should this be recommended. The injection may need repeating depending on the initial response or if there is a reoccurrence of symptoms.
- ACJ excision +/- subacromial decompression.
For those patients with a reoccurrence of symptoms despite the above management options, then arthroscopic ACJ excision +/- subacromial decompression is usually definitive. Injections will be helpful diagnostically in the first instance, confirming the joint as a cause of pain. Where this is confirmed, the surgical procedure typically involves moving a few millimetres of bone from the end of the clavicle to ‘decompress’ the ACJ. These are the surgical treatment options for both arthrosis and osteolysis. This may be combined with a subacromial decompression if there is also evidence of compromise to the subacromial space from the degenerative changes seen to the inferior aspect of the ACJ.
Management of Traumatic cases of ACJ pain
The Rockwood classification is the most widely used system for categorising AC joint separations. The classification system relies on standard radiographs to assess the ligament integrity and displacement patterns. This is a 6-type system that not only takes into account the ACJ joint itself but also the coracoclavicular ligaments and the direction of dislocation in relation to the acromion.
For further information regarding the exact types of ACJ injury, please see here. Classifications in Brief: Rockwood Classification of Acromioclavicular Joint Separations – PMC
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Typically grade 1 and 2 injuries are managed conservatively, with analgesia and relative rest being all that is needed. Surgery is generally recommended for ACJ separations graded 4-6. The treatment of grade 3 injuries remains controversial. Usually, conservative management is recommended initially to see if symptoms will settle, but if the joint remains symptomatic and unstable past three months, surgery may be indicated.
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