The AC joint is one of the 4 joints of the shoulder. It is formed by your clavicle (collar bone) and a segment of your scapula (shoulder blade) called the acromion. It is located on the top of your shoulder and when injured may lead to a bony “bump” on the top of your shoulder (called shoulder separation). Injury usually occurs in the form of trauma that causes disruption to the ligaments of the AC joint, or this joint can be susceptible to degeneration as well. Your therapist can assess your AC joint to see if it is a contributing factor to your pain and create a treatment plan to address your concerns.