Patellofemoral Syndrome (PFS)



This syndrome describes pain in and around the patella (knee cap). It was formerly known as ‘chondromalcia patellae’, but this has fallen out of vogue. It is thought to be secondary to patellar malalignment to the femoral trochlea, resulting in abnormalities within the articular cartilage. It is also thought to be due to a ‘supra physiological mechanical loading and chemical irritation of the nerve endings denoting loss of tissue homeostatsis’- causing an inflammatory cascade and consequent peripatellar synovitis.



At full extension the patella sits lateral to the trochlea. During flexion it moves medially and comes to lie within the intercondylar notch at 10-20°, until 130° when it starts to move laterally again. With increasing flexion, more of the patella articular surface comes into contact with the femur, offsetting the increased load associated with flexion.


Contributing factors:


The VMO (inside quadriceps muscle) in PFS pain sufferers may need to fire earlier to overcome abnormal tracking forces.


The patella is the centrepiece of all the stabilizing forces that act around the knee. It increases effective extension force by as much as 50%. A patellofemoral joint reactive force (PFJRF) is created by compression of the patella against the femur and this force is transmitted to subchondral bone.

The PFJRF increases with increased knee flexion: 15º = 1 times body weight; 20º = 2 times; 45º = 3 times; and 75º = 6 times.



A medial site to the femoral pain is indicative of PFS. The onset of PFS pain is often insidious but may present after an acute traumatic episode. Patients often have a diffuse ache, which may be exacerbated by prolonged sitting (‘movie-goer’s knee’) or activity. It can occur during running and gradually worsens. There may be recurrent clicking or crepitus.



In an open kinetic chain, the hamstrings are predominant in flexion and quadriceps in extension. These exercises (e.g. straight leg raises and knee extensions while wearing ankle weights) place a greater load on the patellofemoral joint and should be avoided early in rehab. In closed kinetic chain exercises (e.g. leg presses or partial squats) there is co-activation of both hamstrings and quadriceps. These exercises strengthen agonist and antagonist muscles simultaneously, result in decreased PFJRF, and are far more physiologic for lower extremity sporting activities.