Plica in the knee is a ridge or fold of the tissues lining the knee joint (synovium).
Normally a plica does not cause problems, but it can become inflamed and thickened from injury or overuse. This is called "plica syndrome." Plica syndrome can interfere with normal joint function and cause pain when the thickened plica rubs over other structures in the knee. It can usually be treated with rest, ice, anti-inflammatory medicine such as ibuprofen, and exercises to stretch and strengthen the muscles around the knee.