Tennis elbow:

It’s a nagging injury that makes even the most casual play painful. It can linger so long that many sufferers resort to surgery. But there’s a new treatment for tendinitis of the elbow that’s less invasive than surgery and more long-term than the anti-inflammatory cortisone. It’s called platelet-rich plasma therapy, and, according to Dr. Allan Mishra, an assistant professor of orthopedic medicine at Stanford and one of the method’s pioneers, it’s one of the only truly biological treatments in use today. It works by enhancing the healing powers of your body, and more specifically, your blood.
That may sound like science fiction, but the process is pretty simple. It goes like this: Doctors take about 30 cubic centimeters of your blood (roughly 1/16 of what you would give when donating blood) and put it in a centrifuge to separate the red blood cells from the white blood cells and platelets. After it’s done processing, about 20 to 30 minutes later, they numb the injured area and inject the plasma containing the platelets and white blood cells into the frayed and degenerated tendon. Then your natural healers—growth factors or proteins within platelets—get to work.

Read more about it here