A dislocated kneecap occurs when the kneecap (patella) is knocked out of place.
It can occur as a result of direct, forceful trauma or due to movement putting excessive pressure on the kneecap, making it a common injury among athletes in sports such as football, basketball, lacrosse, or soccer.
When a kneecap is dislocated, it is common for other parts of the knee to be injured as well; for example, meniscus tears or anterior cruciate ligament (ACL) tears often occur at the same time as the dislocation.
Once it is jolted out of the groove that it normally sits in, the dislocated kneecap can move to either side of the knee, but more frequently will dislocate to the outside of the joint.
Dislocated Kneecap vs. Dislocated Knee
A dislocated kneecap is not to be confused with a dislocated knee. A dislocated kneecap only involves misplacement of the patella, the flat bone that comprises the actual kneecap. A dislocated knee, however, occurs when the entire alignment of the large thigh bone (femur) and shin bone (tibia) is moved out of place.
A dislocated knee is far less common, and a more serious injury, than a dislocated kneecap.
Treatment for kneecap dislocations is usually non-surgical in minor cases, but can involve multiple kinds of surgery for a moderate to severe dislocation.
The Anatomy of Dislocated Kneecaps
The kneecap lays over the point of the knee joint where the thigh bone (femur) and shin bone (tibia) meet. The kneecap sits snuggly in a groove in the thigh bone (the femur), called the femoral groove, and is held in place by a series of ligaments and tendons.
Dislocation occurs when the kneecap is forced out of the femoral groove and its position centered above the knee joint. Damage may also be done to the surrounding bones, cartilage, and/or soft tissues during dislocation.
If an individual finds that the leg cannot be straightened out after a dislocation, damage to other structures of the knee joint is likely and medical consultation should be sought immediately.