Patellofemoral Pain Syndrome - Mechanism

Mechanism

The cause of pain and dysfunction often results from either abnormal forces (e.g. increased pull of the lateral quadriceps retinaculum with acute or chronic lateral PF subluxation/dislocation) or prolonged repetitive compressive or shearing forces (running or jumping) on the PF joint. The result is thinning and softening (chondromalacia) of the articular cartilage under the patella and/or on the medial or lateral femoral condyles, synovial irritation and inflammation and subchondral bony changes in the distal femur or patella known as "bone bruises". Secondary causes of PF Syndrome are fractures, internal knee derangement, OA of the knee and bony tumors in or around the knee.

Specific populations at high risk of primary Patellofemoral Syndrome include runners, bicyclists, basketball players, young athletes and females. Typically patients will complain of localized anterior knee pain which is exacerbated by sports, walking, stair climbing, or sitting for a long time, often called the "Theater Sign" or "Movie-Goers Sign." The pain from prolonged sitting is thought to occur because of the constant pull of the quadriceps muscle on the knee cap while sitting, which causes its impaction against the hard and unyielding surfaces of the bones of knee joint. Descending stairs may be worse than ascending. Unless there is an underlying pathology in the knee, swelling is usually mild to nil. Palpation, as well, is usually unremarkable.