Plica syndrome occurs when bands of remnant synovial tissue are irritated by overuse or injury. Synovial plicae are remnants of tissue pouches found in early fetal development.

These pouches normally combine to form one large synovial cavity, but if the process is incomplete, plicae remain as four folds or bands of synovial tissue within the knee. Injury, chronic overuse, or inflammatory conditions are associated with development of this syndrome.