Anterior knee pain or patellar femoral pain is a common complaint of active individuals, and especially females. Studies have shown that patellar femoral knee pain affects 1 out of every 10 active adolescent girls. Patellar femoral pain is typically associated with an irritation of the underlying surface of the patella due to poor patellar tracking with loaded knee flexion activities. Patellar femoral pain is often characterized as anterior knee pain associated with running, walking, climbing stairs, or any activities that involve repeated or prolonged loaded knee flexion. The cause of patellar femoral pain has been associated with but not limited to such things as over training, increased hamstring, IT band, quadriceps or calf tightness, decreased trochlear groove, increased Q angle and more. The three most common theories for the cause of patellar femoral pain are medial quadriceps weakness (VMO), increased pronation of the foot (flat footed) or weakness and poor functional control of the hip and leg. Although the exact cause is uncertain most physicians agree it is related to abnormal mechanics of the lower extremity. In 2010 a orthopedic study was done examining each of these theories. According to one article it was found that in a group of symptomatic patellar femoral knee pain individuals the medial quadriceps muscle was firing slower than the lateral quadriceps muscle. This was believed to be causing the patella to not set properly in the femoral groove which was causing pain to the anterior knee with activities. Other studies showed that individuals with flat feet referred to as over pronation may have increased knee pain due to the increased rotation and valgus force on the knee with activities. Over the last decade the third theory has been developed indicating abnormal hip biomechanics are too blamed for patellar femoral pain. Studies have indicated that weakness of the hip rotators, abductors and extensor muscles allow for a “medial collapse” of the knee. This suggest that if the hip muscles are unable to control proper hip and leg stability with activities, the leg is allowed to fall into a compromised movement pattern. This increases hip adduction, internal hip rotation causes the patella to not track properly resulting in patellar irritations. With this theory the knee pain is due to how the femur sits in relation to the patella rather than how the patella sits on the femur which is believed in other theories. Clinically this theory is appreciated because patellar femoral pain is closely associated with hip weakness which is often easy to assess with functional testing. If an individual with anterior knee pain wants to successfully get rid of knee pain they first must identify the mechanical deficit and musculoskeletal imbalance through testing and then correct it. Otherwise it is like putting new tires on a car that is out of alignment, your may temporarily resolve the symptoms but not fix the problem only temporally hide it. Early detection of functional limitations and compensations is the best cure and prevention of anterior knee.