Shoulder Surgery

Common AC Joint Problems

Dr. Samuel Koo – Shoulder Surgeon in Seattle, WA


What is the AC Joint?


The AC joint is the acromioclavicular joint. It is the joint where the collarbone (clavicle) connects to the shoulder blade (scapula). Over time, this joint can become inflamed or arthritic. Symptoms of AC joint problems include anterior shoulder pain that is worse when bringing the arm across the body. Non-operative treatment consists of activity modification, anti-inflammatory medications, or a steroid injection into the AC joint. If these measures fail, arthroscopic removal of the distal 1 cm of the collarbone leads to predictable relief of pain.


What are Common AC Joint Conditions?

Joint disruption, usually caused from direct injury, and osteoarthritis in the joint, usually caused from overuse, are two very common AC joint conditions.


Acromioclavicular Joint Disruption


AC joint injuries represent nearly half of all athletic shoulder injuries, usually when the player falls on their shoulder with their arm in adduction (moving towards your body’s mid-line). It can also happen during a direct blow to the shoulder while the humerus (upper arm bone) is adducted (down at your side). There are different degrees of AC joint disruption that require different treatment.


AC Joint Disruption (Rockwood Classification)


Type I – joint sprained without tear of either ligament.
Type II – AC ligaments torn but CC ligaments intact. Lateral end of clavicle not elevated.
Type III – AC and CC ligaments torn, >5 mm elevation of AC joint in unstressed X-ray. Take care to distinguish from type III (distal) clavicular fracture.
Type IV – lateral clavicle separated and impaled posteriorly into trapezial fascia.
Type V – complete separation of clavicle and scapula with gross upward clavicular displacement.
Type VI – as type V but with clavicle detached inferiorly and displaced behind tendons of biceps and brachioradialis.


Osteoarthritis and Distal Clavicular Osteolysis


Osteoarthritis of the AC joint is more often than not, a result of something else, such as injury or repetitive overuse. Often called “weight lifters shoulder”, this condition causes fractures alone the clavicle bone. Overtime those fractures deteriorate and erode the bone. 


What are Symptoms of Osteoarthritis and Distal Clavicular Osteolysis in the AC Joint?


  • Diffuse lateral shoulder pain and/or localized AC joint pain.
  • May be simply an ache in the deltoid area.
  • Often worse at night.
  • Tenderness in the area with exacerbation on passive and active shoulder movements.

Learn about Distal Clavicle Resection: