A: The most likely cause for a bump in that location is osteoarthritis in your sternoclavicular joint. That joint is exactly in the location you described — at the intersection of your breastbone (sternum) and collarbone (clavicle).
It's possible to develop several types of arthritis in this joint, including osteoarthritis, rheumatoid arthritis, psoriatic arthritis and septic arthritis, which is a painful infection in a joint.
Osteoarthritis, the most common form of arthritis, occurs when the protective cartilage that cushions the ends of your bones deteriorates over time. You may be at greater risk of developing osteoarthritis in this joint if you are a postmenopausal woman, have worked in manual labor, or have a history of infection or injury to the joint, such as dislocation.
Osteoarthritis can produce a noticeable bump, which may be mistaken for a tumor. Other signs and symptoms of osteoarthritis include swelling, pain or "crunching" noises when you move your arm. This condition is often treated with rest, anti-inflammatory drugs, activity modification, and sometimes steroid injections or, rarely, surgery.
However, it may not be arthritis. Other possible explanations for a bump include the aftermath of a broken collarbone, a noncancerous lump known as a ganglion cyst or scar tissue from previous joint dislocations. Rarely, a tumor can cause a lump, so getting it evaluated is warranted....
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