AC Joint Dislocation: Grading, Management & Surgery

What Is the AC Joint?

The acromioclavicular (AC) joint connects the outer end of the collarbone (clavicle) to the highest point of the shoulder blade (acromion). It is stabilised by the AC ligament (providing horizontal stability) and the coracoclavicular (CC) ligaments (providing vertical stability).

How Does AC Joint Dislocation Occur?

AC joint injuries most commonly occur from a direct fall onto the top or outer point of the shoulder, common in cycling, AFL, rugby, and horse riding. The clavicle is driven upward relative to the acromion as the shoulder is forced downward.

Grading (Rockwood Classification)

Grade I. AC ligament sprain, no displacement. Grade II. AC ligament tear, minor displacement. Grade III. Complete AC and CC ligament tear, with significant clavicle elevation. Grades IV–VI. Severe displacement (posterior, inferior or superior); require surgical reduction.

Symptoms

• Pain over the top of the shoulder
• A visible "step deformity" (bump) over the AC joint in higher-grade injuries
• Pain with arm elevation and cross-body movement
• Reduced shoulder strength and function

Treatment

Grade I and II injuries are managed conservatively with a sling for comfort (1–3 weeks), ice, analgesics, and early physiotherapy. Return to sport is typically 4–8 weeks.

Grade III injuries are controversial, most can be successfully treated non-operatively, particularly in non-athletes. However, surgical reconstruction is recommended for active patients, manual workers, or those with ongoing pain and deformity after adequate conservative treatment.

Grade IV–VI injuries require urgent surgical reduction and stabilisation.

AC Joint Reconstruction Surgery

Surgical stabilisation involves reducing the displaced clavicle and reconstructing the coracoclavicular ligaments using a graft or synthetic augmentation device. Surgery is performed through a small incision. Most patients return to desk work at 4–6 weeks and sport at 4–6 months.

Further Reading

Dr Yu has written in more detail about this topic on his own site: AC joint instability and AC joint stabilisation surgery.