A bulge in the elbow joint that looks like a bone protrusion can be caused by bursitis, injury, gout stone and other factors. 1. Bursitis: because of some kind of stimulation, such as trauma, infection and rheumatic diseases, leading to the elbow joint bursa part of the damage caused by a kind of inflammation, often lead to the joint part of the swelling, similar to the bulge, and accompanied by the surrounding pain. 2. Injury: mainly because of the elbow joint after the injury, local small blood vessel rupture bleeding or tissue inflammatory exudation, causing elbow area bulging, often accompanied by obvious pressure pain and subcutaneous bruising. 3. Gout stone: because too much purine intake and lead to the body’s uric acid content increases, can easily lead to gout stone deposits in the elbow joint parts of the formation of bulges, accompanied by severe pain. The elbow joint long a bulge, there may be other causes, should be timely to the hospital, to identify the cause of targeted treatment.