Acromioclavicular Joint Sprains (Shoulder Separation; AC Joint Sprain) By Danielle Campagne, MD, University of California, San Francisco Reviewed / Revised Mar 2021 | Modified Sep 2022 View Patient Education Diagnosis Treatment Topic Resources Ligaments of the shoulder... Acromioclavicular Joint Sprain Acromioclavicular joint sprains are common, usually resulting from a fall on the shoulder or, less often, an outstretched arm.