patellofemoral syndrome (PFS)

Last reviewed 05/2021

Patellofemoral syndrome (PFS) is characterized by a group of symptoms that are easily diagnosed and often respond to simple management

• PFS can be defined as retropatellar or peripatellar pain resulting from physical and biochemical changes in the patellofemoral joint
• should be distinguished from chondromalacia, which is actual fraying and damage to the underlying patellar cartilage
  

• typical presentation
  • anterior knee pain that occurs with activity and often worsens when they are descending steps or hills. It can also be triggered by prolonged sitting. One or both knees can be affected
  • there may be knee pain in association with positions of the knee that result in increased or misdirected mechanical forces between the kneecap and femur.

A common misconception is that the patella only moves in an up-and-down direction. In fact, it also tilts and rotates, so there are various points of contact between the undersurface of the patella and the femur

• repetitive contact at any of these areas, sometimes combined with maltracking of the patella that is often not detectable by the naked eye, is the likely mechanism of patellofemoral pain syndrome. The result is the classic presentation of retropatellar and peripatellar pain. This pain should not be confused with pain that occurs directly on the patellar tendon (patellar tendonitis)
• maltracking of the patella may be caused by various factors including:

  • unbalanced muscle pull (of muscles affecting the movement of the patella and patella tendon - rectus femoris, vastus lateralis, vastus medialis)

    • in athletes these muscles (rectus femoris, vastus lateralis, vastus medialis) may become overdeveloped and thus can create maltracking of the patella within the patella groove on the femur, as the patella gets "pulled" by the muscle imbalance created by the overdeveloping of one muscle
  • malalignment between the joint surfaces
  • excessive knee valgus (ie, increased Q-angle) resulting in increased lateral forces
  • quadriceps contractures causing production of excessive leverage forces on the patellofemoral joint surface
  • excessive use of the joint, either in frequency of loading or excessive loading, also contributes to the symptoms

Assessment of maltracking:

• the most common form is rotational malalignment, whereby the patella is tilted, lateral side down. Patella alta or baja, and abnormal position of the tibial tuberosity are other forms of patellar malalignment.
  • several measurements are obtained from the axial or sunrise view on radiographs, from the axial CT plane and from the lateral radiographs of the knee
  • the Q angle is the angle between a line joining the anterior superior iliac spine and the centre of the patella, and a line joining the centre of the patella and the tibial tuberosity. This is a clinical measurement and reflects the degree of valgus transitional force upon the patella. The normal value is 15°
    • some investigators believe that a "large" Q angle is a predisposing factor for patellofemoral pain
  • the tibial tubercle-trochlea groove (TT-TG) distance can substitute the Q angle
    • compares the position of the trochlea groove with the tibial tubercle: two axial CT slices are superimposed, one at the level of the trochlear groove and the other at patellar tendon tibial attachment
      • distance greater than 1.8-2 cm has high specificity for maltracking
  • dynamic MR and CT have been advocated to improve accuracy of imaging modalities mimicking physiological conditions

Management:

• conservative therapy includes:

  • relative rest with consideration of a temporary change to nonimpact aerobic activity;
  • quadriceps strengthening;
  • evaluation of footwear;
  • icing of knee, especially after activity
  • use of NSAIDs
  • definitive treatment should be individualised
    • physiotherapy assessment may result in addition of hip strengthening and stretching or stretching of the iliotibial band, hamstrings and calves
  • use of over-the-counter or custom orthotics should be considered
  • use of knee sleeves and bracing, knee taping - these interventions are controversial
  • patient education is essential - click here for some patient educational material regarding PFS
    
    
• surgery
  • considered a last resort
    • chondromalacia (fraying of the retropatellar cartilage) may be amenable to an arthroscopic surgical procedure to smooth out the undersurface of the patella
  • if the problem is clearly caused by excessive lateral tracking, a "lateral release" is sometimes appropriate

Notes:

• the patella is a sesamoid bone contained within the quadriceps tendon which becomes the patella tendon which inserts onto the anterior aspect of the tibia. The movement of the patella and its tendon is greatly influenced by forces around it
  • these include;
    • 1. rectus femoris
    • 2. vastus lateralis
    • 3. vastus medialis
  • click here for a diagram illustrating the supporting structures of the right patella

Reference:

• 1) Juhn MS. Patellofemoral pain syndrome: a review and guidelines for treatment. Am Fam Physician. 1999 Nov 1;60(7):2012-22.
• 2) Piva SR, Fitzgerald GK, Irrgang JJ, et al. Associates of physical function and pain in patients with patellofemoral pain syndrome. Arch Phys Med Rehabil. Feb 2009;90(2):285-95.

Additional contributions:

Dr Ralph Mitchell BSc (hons) MBChB (April 2011)