The AC joint is found at the tip of the shoulder where the acromion portion of the shoulder blade (scapula) and collarbone (clavicle) join together. The AC joint isn’t as mobile as the large main shoulder joint and only moves when the shoulder is overhead or across the chest (adducted). The joint is partly crammed with a thick pad of cartilage, referred to as the meniscus, wich allows the joint to maneuver . The AC joint is stabilised by its capsule and extra ligaments (coraco-clavicular ligaments).
treatment is NSAIDs, local injections if the arthritis is less severe , if more needs arthroscopic AC joint excision, which gives very quick releif and quick return to sports and overhead activities
The principal cause of AC joint arthritis is use. As a person uses his/her arm and shoulder, stress is placed on the joint. This stress produces wear and tear on the cartilage, the cartilage becomes worn over time, and eventually arthritis of the joint may occur. Another cause is an old injury to the AC joint, such as ACJ Dislocation. Any activity that can put pressure on the joint, either normal or excessive, may eventually cause the arthritis condition.
The Acromioclavicular Jointis usually injured by a direct fall onto the point of the shoulder. The shoulder blade (scapula) is forced downwards and the clavicle (collarbone) appears prominent.
AC Joint osteolysis is essentially a stress fracture of the outer end of the clavicle (collarbone), where it joint the AC joint.
Osteolysis = bone erosion. The bone is eroded faster than it can be replaced or repaired.