A subluxing patella (kneecap) is a temporary, partial dislocation of the kneecap from its normal position in the groove in the end of the thigh bone (femur). This groove is located between two bumps at the end of the thigh bone called the femoral condyles.
This temporary dislocation of the kneecap usually happens during forced leg straightening, with the kneecap moving out of the groove to the outer side of the knee.
The cause is usually abnormal structure in the leg. The inner thigh muscle may be underdeveloped or the outer thigh muscle may be overdeveloped. Your kneecap may be higher in the leg than most people’s kneecaps. You may be knock-kneed or the outer side of the femur bone may be underdeveloped.
You may feel the kneecap moving out of position. You may have swelling and pain behind the kneecap. You may have pain when you bend or straighten your leg.
Your healthcare provider will ask about your symptoms and examine your knee. He or she may be able to feel the kneecap slipping to the outside as you bend and straighten your leg. An X-ray may show underdevelopment of the lateral femoral condyle.
To treat this condition:
Some people need surgery to keep the kneecap from subluxing.
While you are recovering from your injury you will need to change your sport or activity to one that will not make your condition worse. For example, you may need to bicycle instead of run.
Follow your healthcare provider's instructions. Ask your provider:
Make sure you know when you should come back for a checkup.
A subluxing kneecap is best prevented by keeping your thigh muscles strong, especially the group of muscles on the inner side of the thigh.