A knee plica is a naturally occurring fold in the lining of the knee joint capsule. The lining of joints is made up of a thin, slippery tissue called synovial tissue. The synovial tissue in the knee has plica (folds) that allow movement of the bones without restriction. There are four plica synovial folds in the knee joint. The fold that commonly presents itself as a clinical problem is the medial plica, which attaches sideways to the lower end of the patella (kneecap) to the lower end of the femur (thighbone) on the medial or inner side of the knee. Knee plica syndrome and synovial plica syndrome refer to inflammation in any of the four plicae, as a source of pain, stemming from overuse of repetitive motions. Knee plica syndrome is more commonly seen in runners and cyclists. Dr. Riley J. Williams, orthopedic knee specialist, serving Manhattan, Brooklyn, New York City, NY and surrounding areas, has extensive experience in treating knee plica syndrome, synovial plica syndrome and other knee injuries.