Here are many things that can happen to the AC joint, but the most common conditions are arthritis, fractures and separations. Arthritis is a condition characterized by loss of cartilage in the joint, which is essentially wear and tear of the smooth cartilage that allows the bones to move smoothly. Like arthritis at other joints in the body, it is characterized by pain and swelling, especially with activity. Over time, the joint can wear out and get larger, with spurs forming around it. These spurs are a sign of the arthritis and not a cause of the pain. Reaching across the body toward the other arm aggravates arthritis at the AC joint. AC joint wear and tear is common in weight lifters, especially among those who bench press and to a lesser extent, military press. In weight lifters the arthritis at the AC joint has a special name — osteolysis.