Dislocation of the patella (dislocated kneecap)

Arms | Orthopaedics | Dislocation of the patella (dislocated kneecap) (Disease)


Patellar dislocations occurs when the patella (kneecap) moves outside of the patellofemoral groove. Its occurrence is highest amongst young athletes. It involves the patella sliding out of its position on the knee, most often laterally, and may be associated with extremely intense pain and swelling. The patella can be tracked back into the groove with an extension of the leg, and therefore sometimes returns into the proper position on its own. Pain is usually described as being “inside the knee cap”. If displaced, the leg would have a tendency to flex even when relaxed.

Causes and Risk factors

A person with a knee dislocation has a bone in the knee that has come out of place. When an injury tears the ligaments around the joint, the bones may separate, resulting in abnormal alignment of the bones. There are two types of knee dislocations: a dislocated knee joint and a dislocated kneecap. Most knee joint dislocations occur in combination with a knee fracture. Causes of knee dislocations include motor vehicle accidents, sports injuries, and falls.

Diagnosis and Treatment

To assess the knee, the Patellar Apprehension Test may be done in which the patella is moved back and forth while the knee is flexed at approximately 30 degrees.

Also, a patella tracking assessment can be performed by the patient making a single leg squat and stand or, alternatively, lying supine with knee extended from flexed position. A patella that abruptly deviates medially on early flexion is called the J sign, and indicates imbalance between vastus medialis and lateral forces. ...

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