Plicas, fat pad & synovial impingements

Plicas are interesting little membranes in the knee that are formed as part of the development of the knee when a whole bunch of cells are forming a baby human! They are very common and usually don’t cause any problems at all. They have no function after birth.
Occasionally if they are large (they can vary in size), or if there are a few of them (you can have up to 3) or if they are irritated, inflamed and thickened by a direct knock or by overuse then they cause problems. Pain around the kneecap especially on bending is the main problem. Bending type sports such as cycling, rowing and volleyball often create plica problems.
The three plicas are the suprapatella plica above the kneecap; the medial patella plica on the inner side of the kneecap; and the infrapatella plica below the kneecap.
Troublesome plicas will often respond to rest, anti-inflamatory medication and physiotherapy. Sometimes they need to be arthroscopically removed.
The fat pad is a normal and useful structure which sits in behind the patella tendon and helps distibute lubrication fluid around the front of the knee. It can however get enlarged and/or inflamed in the same way as plicas and cause pain at the front of the knee. This is sometimes called 'Hoffa's syndrome'. It is treated the same way as plicas. Similarly the synovial lining of the knee joint cavity may get pinched and become locally swollen and painful. This is called 'synovial impingement syndrome' and is again treated similar to plicas.