“What causes fluid in the knee?”

If it’s on top of your kneecap it is called prepatellar bursitis. This occurs frequently when there is excess pressure applied over the knee cap such as kneeling a lot to do housework or tile work. The initial treatment is to apply ice and compression and use Tylenol or Advil. If it does not subside you should consult your family physician, sports physician or orthopedic doctor.

If you're talking about fluid between the skin and the kneecap, that is called prepatella bursitis. Between the skin and knee cap is a pillowcase called the bursae. Normally the pillowcase is flat or empty. When the pillowcase is irritated, it swells with fluid. Kneeling, crawling, or bumping the front of the knee can cause the pillowcase to swell.
Hope it helps!

Dr. Bose

The most common cause of fluid build up is inflammation. If it is between the knee cap and the skin, it is most likely in the bursa called bursitis. If it is behind the knee cap, it is in the joint itself, called joint effusion. The most common causes of a joint effusion in your age group include arthritis, chondromalacia (damaged articular surface cartilage), and meniscus cartilage tears. Fluid can be related to other disease processes such as rheumatological disorders, ligament tears, fractures and infections, so it is important to be evaluated appropriately to determine the cause and direct treatment specific to your knee. If you have severe pain, fever, difficulty putting weight, redness, warmth or other evidence of infection, it can be an emergent situation that needs to be evaluated right away.

Ron Noy, MD, FAAOS

Fluid can be either around the knee which is bursitis or in the knee which is an effusion. The most common bursitis is called Pre-patellar busitis or “ nursemaid knee”. The fluid can be normal Synovial fluid which has increased production or blood from trauma. The most common cause is from crawling on knee or overuse (squats,lunges, climbing ladders/hills. The blood fluid is from direct contact and sometimes from medications which thin the blood (aspirin, NSAIDS, plavix). Treatment is figure out the cause and modify this (wear knee pads, squat less, bike less etc). Ice, stretching, Tylenol if painful may help but usually will go away and if not provoked stay away. Sometimes a single or multiple drainage is necessary. Sometimes a calcium chip or scar type tissue will need surgery. Surgery is only necessary if the swelling is functionally bothersome or painful. I would suggest if you have a continued problem Discuss this with an orthopedic surgeon. Good luck!

Fluid on the kneecap is called prepatellar bursitis. This occurs after doing activities where you are kneeling frequently, such as laying new carpet. This does not usually require surgery and simply stopping the activity (or wearing knee pads), applying compression, and ice will decrease the swelling.