Patellar Dislocation

Topic Overview

The kneecap (patella) is normally positioned over the front of the knee joint at the base of the thighbone (femur). A kneecap can be dislocated, or moved out of its normal position, when:

  • The kneecap is out of place (patellar tracking disorder) and force is applied, causing dislocation.
  • The foot is firmly planted pointing outward, and the knee is bent with the thigh turned inward. This kind of injury is common during many sports activities.
  • The inner edge of the kneecap is hit, pushing it toward the outer side of the leg.

Symptoms of a dislocated kneecap may include:

  • Severe pain.
  • A misshapen knee that looks like a bone is out of position.
  • A popping sensation, followed by a feeling that something is out of place.
  • Inability to bend or straighten the knee.
  • Knee swelling.
  • Cool, pale skin or numbness and tingling in or below the affected knee.

A dislocation can cause other problems even if the bone pops back into place.

  • If the dislocation was due to a preexisting malalignment, the knee may dislocate again.
  • Ligaments, tendons, muscles, and cartilage in or around the joint may stretch or tear.
  • A piece of bone may break off somewhere in the knee joint.

Related Information

Credits

By Healthwise Staff
Primary Medical Reviewer William H. Blahd, Jr., MD, FACEP - Emergency Medicine
Specialist Medical Reviewer Patrick J. McMahon, MD - Orthopedic Surgery
Last Revised January 9, 2012

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