Dislocated Kneecap

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What is a dislocated kneecap?

Your knee—one of the strongest joints in your body—is where your thighbone (femur) and shinbone (tibia) meet. Your knee joint acts like a hinge, allowing you to move your lower leg back and forth and side to side. Your kneecap, or patella, is the small somewhat triangular bone located in front of the knee. Ligaments and tendons hold your kneecap in place so it can protect your knee joint. When the tendons or ligaments are damaged, the kneecap can move out of place and result in a dislocated kneecap.

The kneecap has a small groove underneath so it can slide back and forth. If your kneecap slides only partly out of the groove, this is called a subluxation. If it moves completely out of the groove, it is a dislocation.

A dislocated kneecap, also called patellar dislocation or dislocated patella, isn’t common; it makes up less than 1% of knee injuries. A dislocated kneecap most often occurs among people who participate in high impact sports. More women experience this type of knee injury than men.

A dislocated kneecap is a medical emergency because there may be severe ligament injury to the knee. Immediate care may help reduce the risk of further damage. The most obvious signs of a dislocated knee are a noticeable change in how the knee looks and severe pain. It is vital at this point that you do not put weight on the injured knee (don’t walk on it) as you seek medical help.

What are the symptoms of a dislocated kneecap?

Aside from severe pain and the obvious misshapen or deformed appearance of the knee, other common symptoms of a knee dislocation include:

  • Inability to put weight on the affected leg

  • A feeling of instability in the knee, as if it may buckle

  • A feeling that the kneecap is shifting or sliding out of place

  • A popping sound when the kneecap first moves out of place

  • Swelling around the knee

  • Bruising around the knee

If you cannot go to an emergency department without putting pressure on your leg, consider calling 911 for assistance.

What causes a dislocated kneecap?

There are two common events that can cause a dislocated kneecap: changing direction suddenly with one foot planted firmly on the ground and twisting your knee, or trauma—a direct blow to the knee. Children, especially girls, may experience kneecap dislocations if their knee ligaments are loose. Loose ligaments can’t hold the kneecap in place.

What are the risk factors for a dislocated kneecap?

The people highest at risk of sustaining a kneecap dislocation are those who play high impact or contact sports, such as football. Since these dislocations can also be caused by a sudden pivot to change direction, people who play sports, such as baseball or soccer, are also at risk. If you have previously dislocated your kneecap, you are also at risk for another dislocation. Other risk factors are obesity or being extraordinarily tall.

Reducing your risk of a kneecap dislocation

You may be able to lower your risk of a dislocating your kneecap by:

  • Strengthening the muscles around your knees

  • Ensuring you are using proper techniques when participating in your sport or activity

  • Practicing pivoting in a safe manner

  • Wearing a protective brace if your doctor or physical therapist suggests it, particularly if you have previously dislocated your kneecap

  • Managing your weight to put less pressure on your knees

How is a dislocated kneecap treated?

In many cases, the kneecap moves back into place on its own after it has dislocated. Your doctor may need to physically move it back into place, a procedure called a reduction of the kneecap. Depending on the severity of your injury, your doctor may order an X-ray to see if there a bone injury, or an MRI to see if there are soft tissues tears such as injuries to a ligament, tendon or cartilage.

Once a dislocated kneecap is back in place, RICE will help with recovery:

  • Rest: Do not bear weight on your knee

  • Ice: Apply ice packs to your knee for 20 minutes at a time, at least every two hours

  • Compression: Apply a compression bandage around your knee. Do not make it too tight so as to affect blood circulation to the rest of your leg.

  • Elevation: Elevate your leg.

You may need a brace to immobilize your knee for a few weeks (usually about three weeks) to allow the kneecap to stabilize. You will also need to use a walking aid, such as crutches, to keep weight off your knee as it heals. Your doctor may recommend non-steroidal anti-inflammatory medications, such as ibuprofen to help relieve the pain and lessen swelling. While you recover, physical therapy will help strengthen your leg muscles to reduce the risk of a future dislocation. Full recovery can take up to eight weeks.

If you have had several kneecap dislocations or the damage to the bone or other knee structures is severe, surgery may be an option. During surgery, an orthopedic surgeon removes or repairs the damaged structures and stabilizes the kneecap.

What are the potential complications of a dislocated kneecap?

Most people who dislocate their kneecap heal fully without any further problems. However, if the kneecap and supporting ligaments do not fully heal, there is the potential for dislocations to occur again. The more often you dislocate your kneecap, the easier it becomes for it to happen again, leaving you with an unstable knee.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Aug 21
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
  1. Kneecap dislocation. MedlinePlus. https://medlineplus.gov/ency/article/001070.htm
  2. Patellar Dislocation and Instability in Children (Unstable Kneecap). American Academy of Orthopaedic Surgeons. http://orthoinfo.aaos.org/topic.cfm?topic=A00707
  3. Patellar Dislocation and Instability. UC San Diego Health.  https://health.ucsd.edu/specialties/surgery/ortho/areas-expertise/sports-medicine/conditions/knee/pages/patellar-dislocation.aspx
  4. Kneecap dislocation – aftercare. MedlinePlus. https://medlineplus.gov/ency/patientinstructions/000585.htm