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Patellar Dislocation

Definition

A patellar dislocation is when the kneecap (patella) slides out of the V-shaped groove in the front of the knee.

The Kneecap
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Causes

It may be caused by:

  • Falling onto the knee
  • A direct blow to the knee
  • Sudden twisting motions
  • Tension that puts side to side force on the patella

Risk Factors

This problem is more common in active children and young adults under 20 years of age. It is also more common in athletes and people in the military.

Other things that may raise the risk are:

  • Intense physical activity
  • Having a V-shaped groove in the front of the knee that is too shallow
  • Knock knees—knees angled inward and touching when the legs are straight
  • Flat feet —fallen arches in the feet
  • Excess pronation of the feet—an inward roll of the feet when walking or running

Other problems that can create instability in the patella are:

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

Symptoms

Problems may be:

  • Hearing a popping sound when the injury happened
  • Knee pain and swelling
  • Not being able to put weight on the knee
  • Feeling the kneecap slide out of the groove
  • Changes in the way the knee looks

Diagnosis

The doctor will ask about symptoms and past health. You may be asked how the injury happened. A physical exam will be done. It will focus on the knee. This may be enough to make the diagnosis.

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

Treatment

It may take up to 6 weeks to recover. The goals of treatment are to put the knee back into the V-shaped groove and to manage symptoms.

The doctor will move the knee back into place. Other treatment may include:

  • Medicine to ease pain and swelling
  • Supportive care, such as resting the area and using cold or warm compresses
  • A brace to keep the knee in line as it heals
  • Physical therapy to help with strength, flexibility, and range of motion

People with a repeat or severe injury or those who are not helped by other methods may need surgery. Options are:

  • Arthroscopic repair of damaged cartilage or to realign ligaments or tendons that stabilize the patella
  • Reconstruction of the medial patellofemoral ligament to help with stability and prevent another dislocation

Prevention

This injury is due to an accident. These are hard to prevent.

RESOURCES:

Family Doctor—American Academy of Family Physicians
http://familydoctor.org

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

CANADIAN RESOURCES:

Canadian Association of General Surgeons
http://www.cags-accg.ca

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

REFERENCES:

Acute patellar dislocation. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/acute-patellar-dislocation. Accessed February 18, 2021.

Duthon VB. Acute traumatic patellar dislocation. Orthop Traumatol Surg Res. 2015 Feb;101(1S):S59-S67.

Unstable kneecap. Ortho Info—American Academy of Orthopaedic Surgeons website. Available at: http://orthoinfo.aaos.org/topic.cfm?topic=A00350. Accessed February 18, 2021.

Last reviewed January 2021 by EBSCO Medical Review Board Laura Lei-Rivera, PT, DPT  Last Updated: 2/18/2021