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Normally, the kneecap (patella) sits over the front of the knee joint. It glides over a groove in the joint when you straighten or bend your knee. When the kneecap dislocates, it moves out of this groove and the supporting tissues can overstretch or tear. A dislocated kneecap should be treated promptly and investigated properly.
What are the common causes?
Kneecap dislocation is an uncommon injury usually caused by a sudden change in direction or when the leg hits the ground. It often happens during sports or dancing moves, but can also occur with every day activities. It’s often seen in teenagers.
When a kneecap dislocates, it shouldn’t be hard to spot as the knee usually looks deformed. Other signs and symptoms are:
- sometimes you hear a ‘crack’
- kneecap may feel out of joint
- surrounding tissue swells up very quickly
- extreme painful
- unable to walk
Very often the kneecap will spontaneously correct itself soon afterwards, which can mean the diagnosis is not made when it’s later seen by a knee specialist.
If it’s not the first time you’ve dislocated your kneecap and you’ve managed to gently manipulate the kneecap back into place, with no major injury, there may be no need to go to hospital. Sit with your leg outstretched and keep it still. Either straighten your knee or ask someone to gently lift up your foot. The kneecap will usually correct itself and the pain should rapidly fade. You can manage any swelling by holding an ice pack to your knee for 10 to 15 minutes every hour for the first day of your injury, and every few hours for the few days that follow. If the kneecap dislocates for the second time or more, a surgical procedure is often necessary to correct the problem and prevent further dislocation.
How is it treated?
If it’s the first time you’ve dislocated your kneecap, the leg will be immediately splinted by paramedics and you’ll be taken to your nearest hospital A&E department. If the kneecap hasn’t corrected itself by the time you get to hospital, a doctor will need to manipulate the kneecap back into place in a procedure called a reduction. You may be given medication to sedate you to ensure you are relaxed and free from pain. When the kneecap is back in place, you may have further tests to check the bones are in the correct position and there is no other injury.
You’ll need about six weeks of physiotherapy to recover. A physiotherapist will give you some exercises, such as straight leg raises, to do at home or in the gym to help strengthen the leg muscles and improve the movement of your knee. You probably won’t need supervised treatment if you’re managing recurrent dislocations yourself. There is a better chance of preventing the kneecap dislocating again if you regularly do the exercises your physiotherapist recommends.
Surgery would only be necessary if there is a fracture with a piece of bone floating in the knee.