Overview
This is a swelling of a fluid-filled sac called a "bursa." It's on the inner side of your knee, between the tibia and the tendons that attach to your hamstring muscle. You have similar sacs near other large joints throughout your body. They act as cushions between your bones and your soft tissues. Normally they have a small amount of fluid inside them. But sometimes they can swell. We call that "bursitis."
Causes
Knee bursitis results from constant stress or friction against your bursa. It is most often caused by overuse. It can happen if you do a lot of running. It's often a problem for active people who are out of shape, or who don't use proper training techniques. It can also be caused by arthritis.
Symptoms
Knee bursitis causes pain and tenderness. You feel it on the inner side of the leg below the knee joint. This pain develops slowly. It gets worse with activity.
Treatment
Treatment options include rest, medications and physical therapy. If these aren't helpful, you may benefit from surgery. Your healthcare provider can create a plan that's right for you.