Functional Anatomy of the PFJ of the Knee

The knee is primarily a hinge joint which allows for flexion and extension movements. The patello-femoral-joint is the joint between the patella (knee cap) and the intercondylar notch of the femur, where the patella tracks during flexion and extension of the knee. This tracking of the patella is largely influenced by the balance between lateral and medial forces acting upon it. The majority of the lateral force acting on the PFJ come from the vastus lateralis (VL) component of the quadriceps muscle and the ilio-tibial-band (ITB). The medial forces acting upon the PFJ are controlled by the vastus medialis (VM) muscle, particularly the oblique portion of this muscle referred to as VMO.

What is PFJ Knee Pain?

PFJ knee pain is an umbrella term used to describe pain underneath or around the patella. It is a very common issue which affects a wide range of people and can be quite non-specific in nature. PFJ pain is often aggravated by activities such as running, going up and down stairs or any activity which loads the PFJ such as squatting down.

What causes PFJ Knee Pain?

The lateral structures of the PFJ are anatomically much stronger than the medial structures and imbalances in these forces can cause abnormal patella tracking during knee flexion and extension. This abnormal patella tracking causes pain and irritation under and around the patella. Imbalances between medial and lateral PFJ forces are commonly a result of poor neuromuscular control of the quadriceps especially delay in timing of activation of VMO compared to VL; as we as tightness in the lateral structures of the PFJ, especially the ITB. There are also some biomechanical factors which contribute to abnormal patella tracking including increased femoral internal rotation, knee valgus and excessive foot pronation. Excessive loads being placed on the PFJ through training overload can also be a contributing factor to PFJ pain.

Treating PFJ Knee Pain

Thorough assessment is required to determine the underlying cause of PFJ pain as there are a number of factors which influence it. For the majority of cases of PFJ pain, addressing the imbalance between medial and lateral PFJ forces is required. This includes Improving the neuromuscular control and timing of muscle activation of VMO with specific exercises, as well as reducing tightness in the lateral PFJ structures with stretches and releases for the ITB and VL muscle. Patella taping is also often beneficial to assist in correcting patella tracking before neuromuscular control has improved in early stages of rehabilitation. Assessing and addressing any biomechanical abnormalities that may be contributing to PFJ pain is also vital, such reducing femoral internal rotation by strengthening the hip external rotator muscles and reducing foot pronation by strengthening the stabilising muscles around the foot and ankle.

By Jack Hickey
Exercise Physiologist at MD Health Pilates

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