Definition

A patellar dislocation occurs when the kneecap slides out of place. The patella is the bone more commonly known the kneecap. It fits securely in a V-shaped groove in front of the knee so that the patella can move up and down when the leg is bent or straightened.

Patellar dislocation is very common. Treatment includes nonsurgical manipulation of the patella, immobilization, medications, and physical therapy. In some cases, surgery may be required to repair damage caused by the dislocation.

Causes

Trauma or abnormal movement at the knee causes patellar dislocation. Examples include:

• A direct blow to the knee or from injury, such as a fall
• Tension that applies force from side-to-side on the patella
• Sudden twisting motions

Risk Factors

Factors that may increase your chance of patellar dislocation include:

• Shallow V-shaped groove on front of your knee.
• Knock knees—knees angled inward and touching when the legs are straight
• Flat feet —fallen arches in the feet
• Excess pronation of the feet—inward roll of the feet when walking or running

Other factors that can create instability in the patella include:

• Weak thigh muscles
• A patella that sits too high on the thigh bone
• Weakened and stretched ligaments from a previous patellar dislocations

Symptoms

Patellar dislocation may cause:

• Extreme pain and swelling at the knee
• Buckling under your own weight
• Stiffness
• Abnormal appearance of the knee

Diagnosis

Your doctor will ask about your symptoms and medical history. A physical exam will be done. This will include a thorough exam of your patella to check for tenderness and swelling. If possible, your doctor will have you walk. Your doctor may be able to make the diagnosis based on your symptoms.

Images may be taken of your knee. This can be done with:

• X-rays
• CT scan
• Computed tomography angiography (CTA) scan
• MRI scan

Treatment

If your patella did not return to the V-shaped groove on its own, your doctor will manipulate it back into place.

Your knee will be immobilized in a brace for stability and support. You may need the brace for up to 4 weeks. Your activities will be limited until your knee is stable again.

Prevention

To help reduce your chance of patellar dislocation, keep quadriceps and hamstring muscles strong with strengthening and stretching exercises.

Ortho Info—American Academy of Orthopaedic Surgeons http://orthoinfo.org

Canadian Orthopaedic Foundation http://www.canorth.org

Panni AS, Vasso M, et al. Acute patellar dislocation: What to do? Knee Surg Sports Traumatol Arthrosc. 2013;21(2):275-278.

Unstable kneecap. American Academy of Orthopaedic Surgeons Ortho Info website. Available at:
http://orthoinfo.aaos.org/topic.cfm?topic=A00350
Updated August 2007. Accessed November 5, 2013.

8/4/2014 DynaMed’s Systematic Literature Surveillance
http://www.ebscohost.com/dynamed:
Cincinnati Children’s Hospital Medical Center. Evidence-based care guideline for conservative management of lateral patellar dislocations and instability in children and young adults aged 8-25 years. Cincinnati (OH): Cincinnati Children’s Hospital Medical Center; 2014 Mar 18.

8/3/2015 DynaMed’s Systematic Literature Surveillance
http://www.ebscohost.com/dynamed:
Tuite MJ, Kransdorf MJ, et al. ACR Appropriateness Criteria® acute trauma to the knee. American College of Radiology (ACR). 2014;11. Available at: http://www.guideline.gov/content.aspx?id=49076. Accessed August 3, 2015.