Patello-femoral pain (PFP), or Anterior Knee pain is located under, or around the patella (kneecap). This condition often involves inflammation of the joint as well as the patella fat pad. The pain can inhibit contraction of the quadriceps muscles and extension and flexion of the knee, creating instability and reduced mobility.
PFP often presents in adolescence following sporting activity such as netball or basketball which involve rotation and knee extension or flexion simultaneously.
The causes of PFP are many but often involve lower limb structural and functional abnormalities that causes patella malalignment.
The patella is a small bone, 4 to 5 cm in diameter, that is positioned anterior to the femoral condyles at the distal end of the femur. Its function is to act as a pulley for the quadriceps muscles in extending the knee. It articulates with the femoral condyles, moving in the sagittal plane. The superior aspect of the patella provides attachment for the quadriceps muscles and the inferior pole is attached to the patella tendon which inserts into the anterior, proximal aspect of the tibia, the tibial tubercle. There are also attachments from the ilio-tibial-band on the lateral side as well as knee joint capsular ligaments to maintain alignment and position.
Problems can arise with abnormal shape and functional position of the patella in relation to the femoral condyles. Both articular surfaces are lined with articular cartilage and this can become inflamed and suffer degenerative changes if exposed to excessive wear and tear.
Excessive wear is most often caused by an imbalance of muscles and ligaments attaching to the patella or excessive rotational pull of those structures in an abnormal direction.
As with any machine, if the joints of the body are well aligned and able to function in that position, then they will continue to function efficiently for an indefinite time. However, if they are not well aligned, then they will degenerate, causing pain and disability.
PFP can be caused by:
- Excessive pronation of the foot and associated internal rotation of the lower leg during the late midstance and propulsive phases of walking, or running gait at a time when the whole lower limb should be externally rotating.
- Excessive external tibial torsion, which is compensated by internal hip rotation, will again causes a torque stress through the knee during gait, along with excessive foot pronation.
- Pelvic instability, associated with weak gluteal (external hip rotating) muscles. This allows internal hip rotation and an increase in genu valgum (knocked-kneed) alignment, as well as increased foot pronation. This is easily demonstrated when performing a single leg half squat, flexing the weight bearing knee. The pelvis will sag on the non-weight bearing side, the weight bearing leg internally rotating, increasing the genu valgum and foot pronation. During ambulation, this is called a Trendelenburg gait.
- Weakness of the Vastus Medialis Oblique muscle, the medial quadriceps, and/or a tight, or overly strong Vastus Lateralis muscle, the lateral quadriceps, will pull the patella laterally, creating malalignment of the patella. Balance between these muscles helps keep the patella aligned in the sagittal plane.
- A tight ilio-tibial band will pull the patella laterally, creating malalignment of the patella. This is often associated with weak gluteal muscles which create a pelvic tilt, tightening the ITB. This may also create trochanteric bursitis.
Treatment of PFP often involves foot orthoses to reduce pronation. Excessive subtalar and midtarsal joint pronation not only creates instability but also internal hip rotation which inhibits gluteal contraction. Therefore, orthoses to balance and control foot function are critical for strengthening exercises for the VMO and gluteal muscles. Treatment programs should also include stretching exercises for the lateral quadriceps, ITB, hamstrings and calf muscles.
If you are suffering from knee pain of any kind, book an appointment with one of our podiatrists for an assessment.