Patellofemoral Pain Syndrome (Runner’s Knee)
Patellofemoral Pain Syndrome (PFPS), also referred to as “runner's knee,” is the term used to describe a pain experienced underneath the patella (kneecap), known as the patellofemoral joint (the joint between the kneecap and the femur [thigh bone]). The patella is designed to glide within a groove of the femur as the knee is flexed and straightened, the greater the flexion of the knee, the more pressure is placed upon the patellofemoral joint. This pressure is increased further if the patella mistracks, or travels more to one side of the groove, and can also cause rubbing and irritation within the joint. This irritation is referred to as PFPS.
The most common cause of PFPS is a muscle imbalance between the vastus lateralis and vastus medialis oblique (VMO) muscles of the quadriceps. These two muscles attach to the top aspect of the patella with the vastus lateralis pulling the patella upwards and outwards, while the vastus medialis oblique pulls the patella upwards and inwards. If one overpowers the other, the result is patellar mistracking resulting in PFPS. PFPS typically presents as gradual onset pain during activities that involve knee bending such as climbing stairs, squatting, kneeling, hopping, or running and can even occur with sustained knee flexion such as prolonged sitting at a desk or in a car.