The joint you're describing is called the sternoclavicular joint (SCJ). It is the site of several problems that occur with aging. Many systemic conditions can cause SCJ pain and swelling. Imaging studies are needed to sort these all out.

Most doctors start with plain X-rays. This gives a two-dimension view of the bones and joints in the area. Any bone spurs, fractures, or arthritic changes will show up on X-ray. CT scans may be needed to show changes in the bone or bone destruction. CT scans show small changes not seen with X-rays or bone scans. MRIs provide more detail when there's inflammation or a tumor or other kind of mass.

The doctor may order some lab work if there's any sign of infection or inflammation. With disorders of the SCJ, it can be very hard to tell exactly what the problem is. All of these studies are needed to determine the underlying problem.