What is the AC Joint in the shoulder?

clavicle (Photo credit: msklibrary)

The top of the wing bone or scapula is the acromion. The joint formed where the acromion connects to the collar bone or clavicle is the AC joint. Usually there is a protuberance or bump in this area, which can be quite large in some people normally. This joint, like most joints in the body, has a cartilage disk or meniscus inside and the ends of the bones are covered with cartilage. The joint is held together by a capsule, and the clavicle is held in the proper position by two heavy ligaments called coracoclavicular ligaments.