In a normal, uninjured AC joint, the clavicle connects smoothly and evenly with the acromion. The acromion is the piece of bone from the shoulder blade that curves over the shoulder. When this joint is injured, it can separate creating an AC joint separation.

There are various degrees of separation labeled from one (I) to four (IV). Unless it's a type IV injury, most types are treated with conservative (nonoperative) care. Whenever surgery is done, the standard operating procedure is to remove the distal clavicle.

This step helps reduce pain and loss of function. Without good reduction (putting the clavicle back in place), the clavicle gets trapped by the muscle causing chronic pain. In some cases, removing the distal clavicle is preventative to avoid the risk of chronic pain that can occur if it's not taken out.