Calcific tendonitis (or tendinitis) occurs when calcium deposits build up in your muscles or tendons. Although this can happen anywhere in the body, it usually occurs in the rotator cuff. The rotator cuff is a group of muscles and tendons that connects your upper arm to your shoulder. Calcium buildup in this area can restrict the range of motion in your arm, as well as cause pain and discomfort. Calcific tendonitis is one of the most commonTrusted Source causes of shoulder pain.