Patellar dislocation or instability

Alternative names
Dislocation - knee cap; Knee cap dislocation

Definition

A dislocated knee cap is when the triangular bone covering the knee (patella) moves or slides out of place. The displacement usually occurs toward the outside of the leg.

Considerations

The doctor will conduct a physical examination, which could provide a visual confirmation of the dislocated knee cap. In addition, touching the knee cap during the examination would confirm that it moves abnormally.

A knee X-ray may be performed, confirming dislocation.

Causes

Dislocated knee caps most often occur in women with certain anatomic features of the knee, which predispose them to this condition.

It is usually a result of sudden direction changes while running. This puts the knee under stress. Dislocation may also occur as a direct result of injury. When it is dislocated, the knee cap may slip sideways and around to the outside of the knee.

The first episode or first several episodes are accompanied by pain and inability to walk. If the condition causing dislocation is left uncorrected, repeat dislocations tend to cause less pain and less immediate disability. However, they remain just as damaging to the patellar/femoral joint.

Symptoms

     
  • Knee cap (patella) is displaced to the outside of the knee  
  • Knee swelling  
  • Knee pain and tenderness  
  • “Sloppy” knee cap; that is, able to move the knee cap excessively from right to left (hypermobile patella)


First Aid

Initial treatment consists of a knee immobilizer or cylinder cast, followed by gentle active range-of-motion (ROM) exercises. Physical therapy should be involved to help regain joint and leg strength, especially the quadriceps muscles. Taping techniques have been explored with variable results.

Surgery may be necessary to “redirect” the patella; this may be either by arthroscopic or “open” surgical reconstruction.

Call immediately for emergency medical assistance if

Call your health care provider if you injure your knee and symptoms of dislocation occur.

Call your health care provider if you are being treated for a disloctaed knee and you notice increased instability in your knee, if pain or swelling return after they initially subsided, or if your injury does not appear to be resolving with time.

Also call if you re-injure your knee.

Prevention

Use proper technique when exercising or playing sports. Maintain strength and flexibility of the knee. Some cases of knee dislocation may not be preventable, expecially if anatomic factors predispose you to dislocation.

 

Johns Hopkins patient information

Last revised: December 4, 2012
by Amalia K. Gagarina, M.S., R.D.

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.