A kneecap (patella) dislocation is a painful injury that occurs when your kneecap is forced out of the vertical (trochlear) groove that it normally slides up and down when you move your knee joint. The pain can vary in intensity, but with this type of injury you won’t be able to put weight on the affected leg.
Symptoms of a dislocated kneecap
When you dislocate your kneecap, you sometimes hear an audible pop and your knee may give way or lock. The pain can be intense and you won’t be able to walk on the affected leg. Swelling and bruising is common and your kneecap may appear visibly deformed.
Causes of kneecap dislocation
The knee joint consists of the thighbone (femur), shinbone (tibia) and kneecap (patella). As you bend and straighten your leg, the kneecap slides up and down within the vertical groove that runs from the bottom of your thighbone to the upper end of the shinbone. It is held in place by a network of tendons and ligaments, which flex as you move your knee.When the kneecap is dislocated, it is pushed out of the trochlear groove. This locks the knee in place and may tear the soft tissues that support the knee joint.
There are two main types of kneecap dislocations:
- An acute patella dislocation is the result of a sudden, acute injury, such as a heavy fall or blow to the knee, which forces the kneecap out of its normal position. Sometimes, a simple turn that twists your knee while the foot remains planted on the ground is enough to dislocate your kneecap. Sportspeople and dancers are particularly at risk of this type of injury. Some people have patellar instability, which means the ligaments and tendons are too loose to support the kneecap effectively, making a kneecap dislocation more likely. More women than men experience kneecap dislocations as they have wider hips and looser ligaments, increasing stress on the knee joint.
- A congenital patella dislocation is the result of a structural abnormality (called trochlear dysplasia) whereby the kneecap does not sit properly within the trochlear groove. Certain conditions are associated with this, including Arthrogryposis and Larson syndrome.
A partial kneecap dislocation is where the kneecap briefly pops out of the groove before moving back into place. This type of injury can also cause serious pain and swelling and may increase the likelihood of a complete kneecap dislocation.
Diagnosing a dislocated kneecap
If you have a suspected dislocated kneecap, diagnostic imaging tests such as X-ray, an MRI scan or CT scan may be used to assess the extent of any soft tissue damage and rule out associated fractures.
Treating a dislocated kneecap
Sometimes a dislocated kneecap can correct itself. This is called a ‘transient dislocation’ and you may not even realise that you had dislocated your kneecap, although your knee is likely to be very sore and swollen.
Depending on the severity of your dislocation, your doctor may treat a dislocated kneecap by gently pushing the kneecap back into place in a procedure called a closed reduction. You will be given local anaesthetic and may also be offered a sedative while this is carried out. You may need to wear a splint and use crutches for a few weeks to keep weight off your affected knee. In some cases, where there is significant soft tissue or cartilage damage, you may need to undergo surgery to repair it and prevent it from dislocating again. After a kneecap dislocation, it is important to follow a proper rehabilitation programme, with exercises suggested by a physiotherapist to strengthen the muscles around the affected knee.
Recovering from a dislocated kneecap
Most people recover from a dislocated kneecap within six to eight weeks and can return to everyday activities. Getting back to sports takes a bit longer – normally three to four months – and it is also a longer recovery time if you have undergone surgery or experienced recurrent dislocations.
Preventing kneecap dislocations
While it’s not always possible to prevent accidents, there are things you can do to reduce your risk of dislocating your kneecap, and particularly recurrent dislocations. Exercises to stretch and strengthen the muscles around the knee can help ensure that muscle stress is minimised. If you play sport, having professional coaching can help you develop good form, which reduces your risk of all types of injury. If you do dislocate your kneecap, don’t force yourself to get back to sporting activities too soon. You need to give your knee sufficient time to recover and follow any rehabilitation programme recommended by a physiotherapist.
For advice about diagnosing and treating a dislocated kneecap or partial dislocation, contact us.
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