When your knee produces too much synovial fluid, the excess fluid causes the bursa behind the knee to expand and bulge and is called a Bakers Cyst.

Adolescent anterior knee pain can often be attributed to Osgood-Schlatter disease (OSD). OSD typically causes pain and swelling below the kneecap. The pain usually gets worse with running and jumping activities. OSD can happen in one or both knees.