Cracking or popping noises coming from your knee are common, especially after you hit age 40. These popping noises are known as crepitus. Crepitus in your knee is often harmless, but it can sometimes indicate another health condition is present or developing.

If you sometimes feel a strange sensation in your knee joint — as if it’s inflated with air or locked into place — it may be accompanied by a strong desire to “pop” the knee back into place.

This can be done safely if you move slowly, carefully, and with intention.

The knee joint is a bit complicated. Layers of cartilage cushion the area between your tibia and fibula (shin) bones to your femur (thigh) bone. Your knee joint is covered by another bone called the patella (kneecap). If you feel any pain while you attempt to crack your knee, stop right away.

Simple stretch to pop your knee

  1. Take the pressure off your knee by sitting down.
  2. Extend your leg straight in front of you and point your toe upward.
  3. Raise your leg up as high as it can go. Bend your knee in and out toward the rest of your body until you hear a pop.

There are two types of knee pops:

  • Pathological knee pops are those that only you can feel or hear.
  • Physiological knee pops are loud enough that everyone can hear.

Knee cracking that’s physiological and frequent is a sign you may need physical therapy or further testing to determine the underlying issue with your knee joint.

Your joints are coated in lubricant called synovial fluid. This fluid contains oxygen and nitrogen, among other elements. Occasionally, the gases from this lubricant can build up and need to be released, causing a “crack” in your knees.

But the causes of crepitus aren’t always so straightforward. In fact, researchers are still working to learn more about what causes these popping and cracking sounds in our joints.

Bones that break and don’t heal correctly and tendons that catch on the ridges of your bones and muscles as you move are other causes of knee cracking.

As you age, the cartilage in your knees can become worn. This deterioration of your knee joint can cause it to feel “creaky” as bone rubs on bone when you move your knees.

Sometimes, pain in your knee joint can be a red flag indicating a knee injury or other developing health condition.

If you’re ever injured and feel a “pop” at your knee at the time of injury, there’s a chance a tendon cracked or a bone fractured. Seek medical attention to see if you need further testing.

Make a doctor’s appointment for your knee if you notice:

  • redness or swelling around your kneecap that occasionally appears
  • fever after exercising or injury
  • tenderness or pain when you touch your knee
  • consistent pain with walking or jogging

Serious symptoms mean you might need to go to the emergency room. These include:

  • inability to bend your knee
  • knee popping or cracking at the time of an injury
  • intense pain
  • swelling that appears without warning or apparent cause

Cracking your knee is safe if pain or injury don’t accompany the sound. Experimenting with joint-loosening exercise, like Pilates and yoga, could make your joints more flexible. You can also ask your doctor for their recommendations.

Don’t ever try to crack a joint that’s giving you pain. Be aware that frequent cracking and popping from your knee could be a sign of injury or another developing health condition that needs medical attention.