What Can Go Wrong With My Kneecap?

Medically Reviewed by Tyler Wheeler, MD on March 15, 2020

Your knee is the largest joint in your body. The kneecap, or patella, is the bone that covers your knee. It helps give the joint strength and structure, which allows your legs to bend and turn safely.

Because your knee has many working parts and carries a heavy load, it’s prone to problems.

If you have any of these issues with your kneecap, see your doctor so you can figure out the right treatment. Some of them can get better with physical therapy, while others may need surgery.


Your kneecap can get knocked out of place, or dislocated, when your leg is planted and you suddenly change direction. It can also happen when something hits your leg and forces it in another direction.

Signs that you’ve dislocated your kneecap include:

  • The joint looks out of place, though it might move back on its own
  • A popping sound or feeling
  • Severe pain
  • You can’t straighten your leg or walk
  • Sudden swelling

Patellar Instability and Dislocation

Your knee also might dislocate without an injury because there’s a problem with the structure. That’s called patellar instability. It’s most common in children and teens, though it can happen in adults, too. Structural issues might include:

  • The kneecap rests in a notch at the end of the thigh bone called the trochlear groove. If that notch is very shallow or uneven, it’s easier for the patella to slide out of place.
  • Your ligaments are looser, making your joints more flexible and likely to dislocate. This is especially true of girls.
  • Cerebral palsy and Down syndrome can cause muscle weakness and balance problems that affect kneecaps.
  • Some children are born with unstable kneecaps.

No matter the cause, symptoms of kneecap dislocation are the same.


This happens when your kneecap slides a little out of place but doesn’t dislocate entirely. It’s also a type of patellar instability.

Symptoms that your kneecap has subluxated include:

  • Pain in the front of your knee
  • A feeling that your kneecap is loose
  • Your knee suddenly buckles


  • In a fall, landing directly on your knee
  • A direct hit to your knee, like slamming it against the dashboard in a car accident

If you break your kneecap, your symptoms might include:

  • Bruises
  • You can’t walk
  • You can’t straighten your knee or keep it straight when you raise your leg

Patellofemoral Pain Syndrome

This catch-all term describes pain in the front of the knee and around the kneecap. Sometimes it’s called “runner’s knee” or a “tracking” problem.

If you have this condition, you might hurt when you:

  • Go up or down stairs
  • Kneel or squat
  • Sit with your knees bent for a long time, such as during a movie or plane ride

You might also hear popping or crackling in your knees when you climb stairs or get up after you’ve been sitting a long time.

Patellofemoral pain syndrome can happen because of strain on your knees, like climbing too many steps. The pain might start because you’ve suddenly started to exercise more, such as going from working out 3 days a week to 6. Or maybe you’ve made your workouts more intense.

Other things that might bring on patellofemoral pain syndrome:

  • Poor exercise technique
  • The wrong equipment, such as shoes
  • Changing your exercise surface; for instance, running on streets after you’ve been running on a track

Patellar Tracking Disorder

Patellofemoral pain syndrome also may come from an alignment problem in how your knee works. When you have misalignment, or a patellar tracking issue, your kneecap can push to one side of the trochlear groove when you bend your knee. That irritates the area, causing pain.

Tracking problems could come from overall alignment issues between your leg and hip. Weak thigh muscles can also be part of the problem.


You can’t avoid every possible injury to your kneecap. But you can take some simple steps to help keep your knees healthy:

  • Wear the right shoes for your activity.
  • Warm up before you work out.
  • Do exercises to keep your thigh muscles (quadriceps and hamstrings) strong and flexible.
  • If you’re going to make your workouts longer or more intense, do it gradually.
  • Cut back on anything that causes knee pain.
  • Stay at a healthy weight -- it lowers stress on your knees.
WebMD Medical Reference


SOURCES: from Nemours Foundation: “Jumper’s Knee.”

American Academy of Orthopaedic Surgeons: “Common Knee Injuries,” “Patellar Dislocation and Instability in Children,” “Patellar Fractures,” “Patellofemoral Pain Syndrome.”

U.K. National Health Service: "Dislocated Kneecap."

Johns Hopkins Health Library: "Patellar Instability."

Massachusetts General Hospital: "Patellofemoral Instability."

Shepard Center Spine and Pain Institute: “Patellar Tracking Disorder.”

Texas Health Physicians Group: “Patellar Tracking Disorder.”

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