What causes the patella to dislocate?
Acute patellar dislocation is caused by force, either from a direct impact or a bad step that uses your own body weight against you. A heavy fall or collision can knock the kneecap out of place. However, it doesn’t always take that much. It may be caused by something as simple as a sudden turn that twists the knee while the lower leg is still firmly planted. Athletes and dancers, who are prone to quick pivots, are common victims of this.
Some people have patellar instability, which means that the tendons and ligaments that hold the kneecap in place are already loose and unstable. This might be caused by a previous injury or by another preexisting anatomical condition. An unstable kneecap will dislocate more easily.
People with congenital patellar dislocation (trochlear dysplasia) are born with the condition. It is often, but not always, related to other developmental abnormalities.
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Who does patella dislocation affect?
Anyone can dislocate their patella through injury. However, certain people are more at risk, including:
- Athletes, especially in high-impact sports.
- Dancers, who are prone to quick pivots.
- Teenagers, whose joints and ligaments are looser from constant growth.
- Women, whose wider hips and looser ligaments put more lateral stress on the knee.
- Big and tall men, whose joints are under more pressure.
- People with patellar instability, especially if they have already dislocated their patella.
Doctors don’t know what causes congenital patella dislocation, but a higher incidence among family members suggests a genetic link. Certain other congenital conditions are also associated with it, including:
- Larson Syndrome.
- Arthrogryposis.
- Diastrophic Dysplasia.
- Nail-Patella Syndrome.
- Down Syndrome.
- Ellis-Van Creveld Syndrome.
What are the signs and symptoms of a dislocated patella?
- An audible pop.
- Buckling of the knee.
- Intense pain.
- Sudden swelling.
- Bruising at the knee.
- Locking of the knee.
- Inability to walk.
- Kneecap visually out of place.
How painful is a dislocated patella?
Dislocations are often very painful, but there is a range. It depends how far out of joint the bone has been forced, and how much the surrounding muscles and ligaments, blood vessels and nerves have been injured. It will always be painful to move the dislocated joint or bear weight on it. You won’t be able to use the limb normally until the joint has been corrected.
If your dislocated patella corrects itself, your pain and mobility may improve. But you should still see your healthcare provider. They’ll check for secondary injuries to the ligaments and guide you through the longer rehabilitation process.
Can you walk with a dislocated patella?
No. The knee will either be locked and unable to straighten or bend, or it will catch and pop when you try to bend it. The joint will be unstable and buckle when you try to bear weight on it. It will also be painful to move it. If you can walk, you may only have a patella subluxation.
If your dislocated patella pops back into place, you may be able to walk afterward. But the knee will still be swollen and painful from the trauma. You shouldn't try to walk if it’s too painful. Always see your healthcare provider anyway to check for any secondary injuries. They’ll likely recommend crutches and a brace when you begin to walk again.
