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Introduction

Knee Pain

Dislocated Patella

A patella dislocation is a dislocation of the kneecap — the patella — from its groove at the knee joint. The knee joint is a meeting of three bones: the thighbone, the shinbone and the kneecap in the middle. Normally, when you bend and straighten your leg, the kneecap slides up and down inside a vertical groove between the bottom end of the thighbone and the upper end of the shinbone (the trochlear groove). A network of tendons and ligaments secure the kneecap within the groove, flexing as it moves.

When the patella dislocates, it’s forced outside of the trochlear groove and can no longer move up and down. This locks the knee and pulls the ligaments out of place, often tearing them. Most frequently (93% of the time), the kneecap pops out laterally, to the side of the groove. Patellar dislocation is usually an acute injury caused by impact or by a sudden turn and twist. Like any dislocation, it is painful and debilitating until it is corrected. But the dislocated knee cap will sometimes correct itself.

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Causes

A dislocated kneecap can be caused by:

  • A blow to the knee, for example if the knee joint collides with another person or object with great force.

  • A sudden change of direction while the leg is still planted firmly on the ground, such as during sports or dancing.

  • Weak leg muscles which puts pressure on the knee joint.

  • A misaligned or elevated kneecap. 

Being tall and/or being overweight increases the risk of dislocation and women are also more at risk.

After a dislocated kneecap, the medial patellofemoral ligament may become torn. This is the ligament that secures the kneecap to the inside (medial) of the knee. Once it is torn it may not heal with the same level of tension as before. This can lead to recurrent dislocation of the kneecap.

Symptoms

If you have dislocated your kneecap you may experience:

  • Obvious distortion of the kneecap, which may look out of place or appear to be at an odd angle.

  • Severe pain in the knee and sudden swelling and bruising.

  • Inability to bend or straighten your leg.

  • Being unable to walk.

  • A painful popping sensation in your knee.

Diagnosis

Knowledgeable healthcare providers can usually diagnose a dislocated kneecap by physically examining the knee and asking you questions about the injury. However, they’ll order radiographic imaging tests to check for any related injuries, such as torn ligaments, cartilage injury or fractures. With patellar dislocation, it is safe to correct the joint first and take pictures after.

If your dislocated patella corrected itself, you might not realize that it was dislocated. A dislocation that corrects itself is called “transient.” Afterward, your knee will still be sore and swollen, but it may look like many other more common knee injuries. In this case, imaging tests can show evidence after the fact that there was a dislocation, along with secondary injuries.

Non-surgical treatments

A person with a dislocated kneecap needs care at the hospital right away. After giving pain medicine, the doctor or another health care provider will gently slide the kneecap back into place while straightening the leg. This quick maneuver is called a reduction. Then, they’ll order an X-ray to check for fractures. 

Sometimes a dislocated kneecap may move back into place on its own if the child straightens the leg before getting to the hospital. If this happens, the doctor will still get an X-ray to check the knee for fractures. 

After a kneecap is back in place, a child will need to wear a knee immobilizer (a brace that keeps the knee straight) on the knee for a few weeks and avoid activities that cause pain, such as walking, standing, and repetitive bending. Kids and teens may need crutches to help with walking. Physical therapy and strengthening exercises help to heal the knee. Often, a person will go see an orthopedic provider (bone specialist) to make sure the knee is healing well.

Surgery