Kneecap dislocations

[Tracie Lynn]

Kneecap (patellar) dislocations occur when the kneecap and the ligaments that hold it in place slide sideways and to the outside of the knee.

The kneecap can slide out of place when people, usually adolescent girls with a knee abnormality, suddenly try to change direction.
The kneecap looks out of place, and people feel pain under the kneecap and cannot straighten the knee.
Doctors can diagnose a dislocated kneecap by examining the knee.
Doctors move the kneecap gently back in place, then apply a knee immobilizer or hinged brace.

(See also Overview of Dislocations.)
Kneecap dislocations differ from knee dislocations (which are much more serious).
Kneecap dislocations are common. They often occur in adolescent girls who have an anatomic abnormality of the knee joint, such as loose ligaments or slightly misaligned bones.
Usually, the kneecap slides out of place when people suddenly try to change direction. Kneecap dislocations may occur in sports that involve sudden twisting of the knee and/or impact (such as soccer, gymnastics, baseball when swinging a bat, and ice hockey). They can also occur when people trip or slip.
Sometimes the force that caused the dislocation fractures the cartilage on the back of the kneecap or causes a small piece of the end of the thighbone to break off.