AC Joint Separation involves the acromioclavicular joint (also called the AC joint). The AC joint is where the collarbone (clavicle) meets the highest point of the shoulder blade (acromion). If the force is severe enough, the ligaments attaching to the underside of the clavicle are torn. This causes the “separation” of the collarbone and wingbone. The wingbone actually moves downward from the weight of the arm. This creates a “bump” or bulge above the shoulder.
The injury can range from a little change in configuration with mild pain, to quite deforming and very painful. Good pain-free function often returns even with a lot of deformity. The greater the deformity, the longer it takes for pain-free function to return.