pain syndrome (PFPS) is a common knee disorder, which often affects
the senior athlete and those involved in running and jumping sports.
Overuse, a change in activity, and an altered metabolic status are
frequently responsible for the development of PFPS. Structural alignment
and muscular weakness or imbalance may cause the patella
(kneecap) to track improperly on the femur (thigh bone)
during movement, leading to pain around the kneecap.
Other terms for patellofemoral pain are: retropatellar pain, peripatellar
pain, anterior knee pain, and runner's knee.
Different disorders that cause pain around the kneecap include:
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- infrapatellar tendonitis (jumper's knee), which
affects the tendon just below the kneecap
- chondromalacia patella, which involves damage
to the cartilage surface of the patella
- quadriceps tendonitis, which affects the tendon
attachment above the patella
- plica syndrome, in which joint tissue becomes
inflamed and/or stiff, causing pain and tightness in the joint
What is the patellofemoral joint?
As the knee bends and straightens, the patella slides within a slot
on the femur called the trochlear groove. The patella
moves in many directions within this groove to provide efficient,
frictionless movement up and down, side-to-side, rotational, and tilting.
The bone surfaces are covered with articular cartilage
to make joint movement smooth.
What is patellofemoral pain syndrome and what can cause it?
Repeated abrasion on any of the surfaces of the patella and femur
stresses the soft tissues of the patellofemoral joint and may even
lead to a bone bruise. In some cases, the pain is caused by a weakening
of the articular cartilage and/or swelling within the joint.
One or more of the following factors can lead to patellofemoral pain:
- Overuse: the repetitive bending and straightening of
the knee that occurs in running may lead to the disorder because
of the increased pressure points between the patella and femur
when the knee is bent. A constant bending motion, especially on
the weighted leg, can irritate the patella and cause a bone bruise
- Alignment: The quadriceps alignment between the hip
and the knee (the
Q angle) is thought to affect patellar tracking. Patients
with a larger than normal Q angle (greater than 20 degrees) may
be more susceptible to patellofemoral pain because the patella
has a tendency to track more laterally (to the outside).
Pain may be felt more on the outside of the patella and femur
because of increased pressure on these contact areas. The Q
angle of growing female athletes enlarges as the pelvis widens
during the maturing process, increasing the risk for patellofemoral
- Muscular weakness: A weakness or strength imbalance of
the quadriceps muscles may alter the tracking of the patella.
- Muscular tightness: Tight muscles and tendons may also
affect patellar tracking. The muscular structures that cause movement
in the knee and hip must be flexible. If any one muscle or
muscle group is tighter than the rest, patellar instability can
- Flat feet (excessive foot pronation): Patients
with little or no arch in the foot are also likely candidates
for patellofemoral pain. As the foot rolls inward, the tibia compensates
by rotating inward, disturbing the normal mechanics of the patellofemoral
- A decrease in patellar mobility: the kneecap tightens,
losing its normal ability to move in many directions.