Patellofemoral pain syndrome (PFPS), also known as runner's knee, is a condition characterized by knee pain ranging from severe to mild discomfort seemingly originating from the contact of the posterior surface of the patella (back of the kneecap) with the femur (thigh bone). It is "anterior knee pain involving the patella and retinaculum that excludes other intra-articular and peri-patellar pathology".[1]