Patellofemoral pain syndrome is one of the most
common causes of knee pain in young athletes. The condition is an overuse injury
that results from activities that cause pressure or friction on the cartilage
behind the kneecap. Patellofemoral pain syndrome occurs frequently in athletes
who participate in sports that involve running, jumping, or squatting.
The kneecap functions as a shield to protect the
front of the knee. As a result, direct impact to the kneecap can cause damage to
the cartilage that lines the back surface of the kneecap. In addition, the
kneecap functions as a fulcrum to help the quadriceps (thigh muscles) straighten
the knee. In this capacity, there is pressure on this same cartilage behind the
kneecap that is related to how hard the quadriceps are contracting
(Fc) and how bent the knee is (β) (see Figure 1). It is
not unusual for the pressure on the back of the kneecap to exceed 1,000 pounds
during an activity such as a simple squat.
In addition to pressure that can occur from
bending the knee, the cartilage behind the kneecap is susceptible to friction as
the knee moves between bending and straightening. The kneecap normally slides or
tracks in a groove on the end of the thigh bone. When the kneecap tracks in the
center of this groove (Figure 2a), the pressure is spread over the widest
possible area. This minimizes areas of stress concentration and is considered
the most efficient pattern for the kneecap handling the stresses associated with
activity. When the kneecap is tilted or tracks outside of this groove, the
pressure is unevenly distributed and the excessive forces may be more likely to
cause knee pain (Figure 2b). This abnormal tracking can occur from a variety of
causes including flatfeet, knock-knees, internally rotated femur (thigh bone),
externally rotated tibia (shin bone), or weakness of the hip or thigh
Athletes with patellofemoral pain syndrome
usually participate in running or jumping sports such as basketball, volleyball,
track, or cross-country, and the pain often comes on when there has been a
recent increase in training intensity or volume. Athletes report pain that is
generally located around or behind the kneecap. The pain is worse when running,
jumping, squatting, climbing stairs, walking downhill, or sitting for long
People with flatfeet, intoeing, or knock-knees
may be at higher risk for this condition because these conditions affect how the
kneecap tracks. Athletes with tight hamstring and quadriceps muscles or weak
thigh and hip muscles may also be at risk because of the effect these
abnormalities have on pressure on the kneecap or tracking.
There are a number of other conditions that can
cause pain around the kneecap. Pain that is localized to the bump below the
kneecap may be Osgood-Schlatter disease. Pain that is localized to the patellar
tendon attachment (at the bottom of the kneecap) may be patellar tendonitis or
it may be due to an irritated growth plate. Pain on the outer portion of the
knee or pain that is worse running down hills may be due to a condition called
iliotibial band friction syndrome.
Because the treatment varies for different
conditions, it is important to confirm the diagnosis and source of pain before
beginning treatment. Pain that is associated with swelling, locking,
instability, or disruption of daily activities or is in association with fever
or other illness should be evaluated.
Treatment for patellofemoral pain syndrome
involves limiting running, jumping, squatting, or other pain-causing activities.
Ice and anti-inflammatory medications can help reduce pain. Cross-training
activities, such as swimming or low-resistance cycling, may be continued to
maintain fitness provided that these activities do not cause pain.
The key to resolving patellofemoral pain
syndrome is identifying and correcting the causes of the pain. The treatment for
a particular individual with patellofemoral pain syndrome will depend on which
of these causes seems to be contributory. Once the causes have been identified,
the treatment requirements are usually obvious. Your doctor, a physical
therapist, or a certified athletic trainer can help you identify causes and
recommend specific treatments. They can also help monitor recovery and provide
guidance for a gradual and safe return to sports activities.