Dislocated Knee

What is a dislocated knee?

A dislocated knee occurs when the kneecap (patella) pops out from its normal position. This can occur as the result of force or — more often — is related to a developmental condition that leads to an improper alignment of the kneecap with the thighbone (femur). This is sometimes called "unstable kneecap."

What are the symptoms of a dislocated knee?

Each child may experience symptoms differently. The most common symptoms include:

  • pain in the front of the knee that increases with activity
  • swelling and/or stiffness
  • kneecap slips off to the side
  • difficulty using or moving the leg in a normal manner
  • deformity of the dislocated area
  • warmth, bruising, or redness in the injured area
  • creaking or cracking sounds during movement

Because the symptoms of a dislocated knee may resemble other conditions or medical problems, always consult your child's doctor for a diagnosis.

What causes a dislocated knee?

The kneecap connects all the muscles in the thigh to the shinbone (tibia). As you bend or straighten your leg, the kneecap is pulled up or down. The thighbone has a v-shaped notch at one end to accommodate the moving kneecap.

In a normal knee, the kneecap fits nicely in the groove. However, if the groove is uneven or too shallow, the ligaments are loose or there is a sharp blow to the kneecap, the kneecap could slide off, resulting in a partial or complete dislocation.

Who is at risk for a dislocated knee?

Kneecap dislocations typically occur in active teenagers and young adults from the ages of 14 to 20 years old. They are most common in teenage athletes who participate in contact sports, such as football, and those suffering simple falls from a wide variety of activities, such as gymnastics, dancing, or cheerleading. A family history of knee instability that leads to dislocation is present in one-fourth of patients with dislocated patellas.

How we care for dislocated knees

If your child is physically active and participates in contact sports and other activities, they may be more prone to having a dislocated patella. While our team of doctors at the Boston Children’s Hospital Lower Extremity Program is committed to helping stabilize and restrengthen your child's knee, they're also interested in helping active young people prevent these injuries in the first place.