Dislocated Kneecap

What is a Dislocated Kneecap?

A dislocated kneecap also known as patellar dislocation is when the patellar bone, a triangle shaped bone on the knee is moved out of position due to heavy blunt force trauma. The condition is associated with extreme pain and a gross deformity of a bone out of position is displaced laterally that is easily visible on physical examination.

Anatomy of the Patellar bone

To understand dislocation of the kneecap, we need an anatomic understanding of the knee.

Image result for hamstring tendonitis Patellar bone

The Patella is a sesamoid (sesame seed) bone that is embedded in the within the tendon of the quadriceps femoris muscle. It protects the anterior portion of the knee joint.

The lower horizontal fibers of the vastus medialis and the large size of the lateral condyle of the femur in preventing lateral displacement of the patella have been emphasized. Sometimes, the recurrent dislocations of the patella are caused by underdevelopment of the lateral femoral condyle.

Traumatic injury to the quadriceps attachments of the patella (particularly the vastus medialis) results into dislocation of the patella with or without fracture.

Patellar dislocations are common in young females and athletes, usually they present with an instability coupled with a deformed knee. An effusion of fluid can be seen on radiologic examination. Direct trauma or a flexion with external rotation on the valgus may cause the injury.

Dislocated Kneecap

A lateral dislocation is the most common type of patellar dislocation. Another type is horizontal in which the patella has rotated on its horizontal axis with the surface facing distally or proximally.

Another one is vertical wherein the patella rotates on its vertical axis with impaction of one of the lateral surfaces in the intercondylar notch of the femur.

The last one is intercondylar where the patella remains in place but is rotated either vertically or horizontally.

Several other factors influence the risk of patellar dislocation such as a lateralized tibial tubercle, tibial tuberosity-trochlear groove distance and the shape of the patella.

Reduction of a lateral dislocation is a simple and safe procedure. Otherwise, an orthopedist should be consulted for these more uncommon types of dislocations.

Anesthesia is not usually required during reduction but some patients may have anxiety and pain so sedation may be required to ensure maximal patient comfort.

Signs and Symptoms

The signs and symptoms of a dislocated kneecap include

  1. Deformed knee readily visible
  2. Inability to straighten out leg
  3. Patella is readily seen outside of its normal position
  4. Knee pain and swelling
  5. Sloppy knee characterized by a moving patella


Once the patient has been identified to have a lateral patellar dislocation, a simple reduction can be done which is safe and easy to perform.

The patient is informed about the procedure as the physician stand at the side of the affected knee ready to perform the reduction. The leg is flexed at the hip to reduce the tension of the quadriceps muscle.

An anteromedial force is applied while extending the knee and the patella locks into position. If the dislocation is medial the same process as in anterolateral force is applied.

Once the reduction is complete a splint is left in place to fix the knee and prevent further mobilization. A follow up with a surgeon may be needed for complete dislocation that needs surgical intervention.

Once the reduction is complete, rehabilitation of the knee begins that takes about 6 months before complete healing takes place. Splints are placed on knee to immobilize it and when physiotherapy is needed, removed to make some active movements to prevent disuse atrophy.

Intra-arterial injections of corticosteroids may help resolve the inflammation of the affected area and hasten the healing process.


When the kneecap has been dislocated but rapid reduction of the dislocation is done, the patient suffers no permanent, disabling effects and may continue activities of daily living unhampered.

The rate for complication increases as time goes by where no medical attention is given and the kneecap continues to be out of anatomic position. Osteochondral fractures, degenerative arthritis and recurrent dislocations may result.

While the knee is in a state of recovery, interventions such as the RICE method should be employed to hasten the healing process. Rest, Ice Compress and Elevation of the affected leg to increase blood flow are highly recommended. Nonsteroidal, anti-inflammatory drugs can be used to manage the pain in the convalescent period.


The kneecap or patellar bone is located in a crucial position to protect the knee joint from trauma and also functions to reduce the friction that it suffers during daily activities of living. But this position also put the kneecap in a position where it can easily be moved out of place and cause extreme pain.

Care must be taken not to exert tremendous force on the patellar bone by not suddenly twisting the knee. If the force in the rotation is greater than the force the quadriceps tendon can handle, the vastus medialis gives way leading to its dislocation.

The gross deformity, pain and swelling are easily visible to the physician and require reduction to return the affected knee to normal functioning.

With good care and rest, the patient suffers no ill effects and can continue to perform activities of daily living.

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