Patellofemoral syndrome (PFS) is a condition caused by the patella - a unique, non-weight bearing structure at the front of the knee - not tracking correctly over the femur. The patella normally rides in a groove on the femur and acts a fulcrum, giving leverage to the large quadriceps muscle group so that those muscles can generate more force. If there is an imbalance in these muscles this pulls the patella out of it's normal groove and often results in PFS, characterised by pain under or around the patella.