Why Does a Knee Cap Dislocate?

by Jsantos, August 10, 2013

Why Does a Knee Cap Dislocate?

Medically referred to as patellar dislocation, this condition occurs when the knee cap itself becomes dislocated. According to the exact definition on Duke University’s health website, “a patella dislocation or patellar subluxation occurs when the triangle-shaped bone covering the knee moved out of place.” It can be caused by several different factors and can be painful and physically limiting.

However, it can be treated by an orthopedic surgeon. Just what causes a knee cap dislocation, though?


A sudden twisting movement is most often the cause of dislocation. If the patient’s foot is planted on the ground and then the leg is twisted quickly and forcefully, this could cause the problem. That’s because the sudden and fast pressure on the knee itself can be more than the ligaments that hold the cap in place can handle.

Changing Direction

Often, knee cap dislocations happen to runners because they may change direction quickly. For some runners, this sudden change in motion can either cause a Luxated or dislocated patella. This occurs because the sudden change in direction connected with speed and placement of the foot can put too much pressure on the joint.

Direct Impact

Direct impact on the knee cap is not as common of a cause for dislocation, but it is possible. In this case, if an athlete is hit directly on the knee (or if anyone falls or hits their knee violently on something), then this can force the knee cap out of place. Again, in this instance, the pressure on the ligaments that hold the cap is enough to push them out of the proper location.

Knowing If You Have a Dislocated Knee Cap

There are different types of knee injuries, so if you have suffered from something that may have caused dislocation, consider a few things. First of all, did you go through any activity that would have caused one of the above situations, like twisting, sudden movement, or impact? If you did, then consider the symptoms of a dislocated knee cap:

  • Pain that is so severe that you can’t walk on the leg.
  • The knee becomes very tender or swollen.
  • The knee feels extremely unstable or shaky.
  • The knee collapses with weight.
  • You can see or feel the knee cap slip out of place.

Getting a Diagnosis

Of course, you can’t diagnose a displaced knee cap on your own. You will need to see an orthopedic surgeon. Your doctor will use different types of exams and tests to determine if you do have a dislocated knee cap and not some other injury like fractures. Some of the ways that this problem may be diagnosed include:

  • X-rays
  • Physical examination
  • MRI

Through these tests, your surgeon can ensure that you do not have any further injuries, like damage to the ligaments, broken bones, or injury to other parts of the knee. Once other problems have been ruled out, your doctor will be able to move on to treating the dislocated knee cap. If there is other damage, you may have to consider further treatments, including surgery.


The most common treatment for a dislocated knee cap is to physically push the knee cap back into place. This is called physical relocation or reduction. After this is done, you will need to wear an immobilizing brace for several weeks and you will most likely need to go through physical therapy. If you continue to suffer from knee dislocations in the future, then arthroscopic surgery may be required.

There are different reasons why your knee cap may become dislocated. If you suffer from an injury that involved direct impact to the knee or if you do any quick twisting of the leg with your foot planted, then this can cause the condition. If you think you have a dislocated knee cap, it’s important to see a doctor as soon as possible.


Duke University Health, http://www.dukehealth.org/orthopaedics/services/knee-treatments/care-guides/kneecap-dislocation

University of Connecticut Health, http://nemsi.uchc.edu/clinical_services/orthopaedic/knee/patellar_dislocation.html



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