Acromioclavicular Joint (AC Joint) Definition

The acromioclavicular joint is located where the collarbone meets the highest point of the shoulder blade. It is one of the four joints that complete the shoulder joint. The AC joint is instrumental in allowing the arm to move above the head.

Cartilage degeneration in the acromioclavicular joint may lead to acromioclavicular osteoarthritis, the most common type of shoulder arthritis.

Anterior view of the shoulder joint labeling the sternoclavicular, acromioclavicular, glenohumeral, and scapulothoracic joints.