Upper Limb · 4 min read
The AC Joint: Small Structure, Big Impact on Shoulder Function
The acromioclavicular joint is sometimes called the 'forgotten joint' of the shoulder. Clinicians who manage it thoughtfully — understanding both its biomechanical importance and the evidence on when intervention adds value — produce outcomes that remind patients and athletes why it should never be forgotten.
The acromioclavicular joint transmits forces between the upper limb and the axial skeleton during virtually every overhead and loaded activity of daily life. Despite its small size, its disruption in high-energy injury or its progressive arthritic degeneration in older and athletic populations produces symptoms that are functionally significant and, in the right clinical context, highly treatable with excellent outcomes.
Traumatic AC joint injuries: a nuanced evidence base
The Rockwood classification provides a clinically useful anatomical framework for AC joint injuries. Type I and II injuries — partial disruptions — are managed conservatively with excellent results. Type III injuries — complete disruption of both the AC and coracoclavicular ligaments — sit in genuinely contested territory in the evidence base: multiple prospective studies comparing early operative fixation to non-operative management have not demonstrated consistent superiority for surgery at two-year follow-up. For most patients with Type III injuries, a structured non-operative programme with a clear functional review at three months is the well-evidenced first step.
For Type IV, V, and VI injuries, surgery is appropriate and produces reliable results when performed in a timely fashion by an experienced upper limb surgeon. The principle that guides decision-making is straightforward: the severity of the injury determines the likelihood that spontaneous functional recovery will be adequate for this patient's demands. Matching that assessment to a transparent conversation about what operative and non-operative pathways involve produces well-informed, confident patients whatever path they take.
Acromioclavicular joint arthritis: an underdiagnosed cause of shoulder pain
Degenerative AC joint arthritis is a common and frequently underdiagnosed source of anterior superior shoulder pain, particularly in athletes who perform repeated overhead loading. Clinical examination — specific tenderness at the AC joint line, a positive crossbody adduction test, and reproduction of symptoms with the Paxinos test — is highly informative. A targeted ultrasound-guided corticosteroid injection that relieves symptoms confirms the diagnosis and provides valuable therapeutic relief.
The AC joint may be small, but its contribution to shoulder biomechanics and pain is never small. It deserves the same thoughtful clinical assessment as every other structure in the shoulder complex.
For patients with end-stage AC joint arthritis that has not responded adequately to conservative management, arthroscopic or open distal clavicle excision produces excellent results — one of the most reliably satisfying procedures in shoulder surgery, with high patient satisfaction and a low complication profile in experienced hands.
💬 How systematically do you assess the AC joint as part of your shoulder examination? Is it the first structure you examine, or is it an afterthought?