Patellofemoral Pain Syndrome

Patellofemoral pain (PFP) is diffuse anterior or retropatellar knee pain provoked by loading a flexed knee. It is one of the most common causes of knee pain in adolescents and young adults, and is still often called patellofemoral pain syndrome.

It is more common in females, with a female-to-male ratio of about 2:1 and peak incidence at ages 15 to 30. A systematic review reported an annual prevalence of about 23% in the general population and 29% in adolescents.

It is a clinical diagnosis, often persistent or recurrent, and a recognised risk factor for later patellofemoral osteoarthritis.

The patella, the largest sesamoid bone, articulates with the femoral trochlear groove and acts as a fulcrum for the quadriceps. Patellofemoral joint reaction forces rise rapidly with knee flexion, reaching several times body weight at 90°, which is why squatting, stair descent and prolonged sitting provoke pain. Dye's envelope of function frames PFP as loading that exceeds the tissue's homeostatic capacity rather than a fixed structural lesion.

PFP is multifactorial and biopsychosocial, not simply vastus medialis obliquus (VMO) weakness or maltracking:

• •Local: quadriceps weakness and pain-related quadriceps inhibition
• •Proximal: hip abductor and external rotator weakness, driving dynamic knee valgus in single-leg loading
• •Distal: excessive foot pronation and reduced ankle dorsiflexion
• •Training errors, and psychosocial factors such as fear-avoidance, catastrophising and low self-efficacy, which affect persistence

Chondromalacia patellae is a pathological finding, not a clinical diagnosis, and is commonly incidental on MRI.