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Dislocation of the Kneecap

Dislocation of the Kneecap

A dislocation of the kneecap occurs when the knee cap pops sideways out of its vertical groove at the knee joint. It’s usually caused by force, from a collision, a fall or a bad step. A dislocated patella is painful and will prevent you from walking, but it’s easy to correct and sometimes corrects itself.

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.

Types of Dislocation of the kneecap

Most of the time, a patella dislocation is an acute injury caused by force. This is called acute patella dislocation. It’s a relatively common injury, since the kneecap takes less force to dislocate than some other joints do. It’s also relatively easy to pop back in. Rarely, patella dislocation can also occur developmentally, from a condition called congenital patella dislocation (or trochlear dysplasia). When the patella develops outside of the trochlear groove, it can’t be moved back into place. These cases require surgery to correct.

A “dislocated knee” involves the other two bones that make up the knee joint: the thighbone (femur) and the shinbone (tibia). When your knee is dislocated, the femur and tibia no longer connect at the knee joint. One of the bones has been forced backward or forward relative to the other bone. A dislocated knee (tibiofemoral dislocation) is rarer and more serious than a dislocated kneecap, because of the force required to misalign the leg bones and the damage it does to the ligaments.

Causes of Dislocation of the kneecap

Acute patellar dislocation is caused by force, either from a direct impact or a bad step that uses your own body weight against you. A heavy fall or collision can knock the kneecap out of place. However, it doesn’t always take that much. It may be caused by something as simple as a sudden turn that twists the knee while the lower leg is still firmly planted. Athletes and dancers, who are prone to quick pivots, are common victims of this.

Some people have patellar instability, which means that the tendons and ligaments that hold the kneecap in place are already loose and unstable. This might be caused by a previous injury or by another preexisting anatomical condition. An unstable kneecap will dislocate more easily.

People with congenital patellar dislocation (trochlear dysplasia) are born with the condition. It is often, but not always, related to other developmental abnormalities.

Symptoms of Dislocation of the kneecap

  • An audible pop.
  • Buckling of the knee.
  • Intense pain.
  • Sudden swelling.
  • Bruising at the knee.
  • Locking of the knee.
  • Inability to walk.
  • Kneecap visually out of place.


Orthopedic Surgeon at Shreya Hospital 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.

Treatment of Dislocation of the kneecap

Reduction: As long as the diagnosis is clear, a knowledgeable healthcare provider will manually relocate the kneecap as soon as possible. This is called a reduction. A patellar dislocation injury that occurs on the playing field can be reduced immediately by a trained healthcare provider if there is one on-site. If you go to the emergency room, they may give you sedatives and pain medication first. They’ll usually correct the joint first and then look at it on an X-ray.

Imaging: Healthcare providers will take imaging tests to see that the kneecap has been properly replaced and plan any additional treatment. X-rays and CT scans can help reveal any preexisting anatomical conditions that may have contributed to the dislocation, as well as any additional injuries. An MRI can give more detailed information on the cartilage and ligaments if it’s needed. Sometimes an MRI will reveal a previous transient dislocation that wasn’t suspected before.

Surgery: If there is significant damage to the bone or to the cartilage and tendons of the knee, your healthcare provider may recommend surgery to repair it. Surgery may also be recommended if you have recurrent patellar dislocations or chronic patellar instability. Repairing and strengthening the cartilage and ligaments is a preventative measure to restabilize the knee. When patellar dislocation is congenital, the joint can only be repaired through surgery.

Rehabilitation: You’ll be sent home with painkillers and a splint for the first few days. Periodically elevating and icing the joint can help keep the swelling down. You’ll begin walking again gradually with crutches and a brace to hold the joint in place. Physical therapy is very important to restrengthen the muscles while limiting the range of motion until the joint is restabilized. It takes about six weeks to three months to fully recover from a dislocated patella.