An AC (acromioclavicular) joint sprain occurs when an injury damages the ligaments in the AC joint, which is where the shoulder blade meets the collarbone. The highest point of the shoulder blade is called the acromion, and strong tissues called ligaments connect the acromion to the collarbone, forming the AC joint. AC joint sprains can be caused by falling onto your shoulder, falling onto an outstretched hand, or getting a direct blow to your shoulder. Symptoms of an AC joint sprain can include shoulder pain, soreness, swelling, bruising, change in the shoulders shape, bulge above the shoulder, shoulder that appears to droop, collarbone that moves upward, and limited movement in the shoulder. Treatment for an AC joint sprain will depend on how serious the strain is and may include rest, a sling, cold packs, and prescription or over-the-counter medicines. In some cases, surgery may be necessary.