Why Do My Knees Crack? | 3 Reasons, How To Stop It, And When You Should Be Worried

An old man holding his knees

Before becoming a physical therapist, I always wondered: “Why do my knees crack so much? Am I injured?” They’ve always been noisy but painless.

It scared me – I thought I was buying a ticket straight to knee surgery. My knees always crack and pop when I climb stairs and when I do squats. There must be something wrong, right?

Years later, I learned that, that sound – called crepitus- is common in most healthy knees.

Studies suggest that 99% of knees make noises. These are usually due to bubbles within the joint or tissues rubbing against each other.(1, 2)

It’s nothing to worry about as long as it’s painless and it doesn’t restrict your range of motion.

Here are some common reasons why healthy knees crack:

What causes knees to crack and pop?

1. Synovial fluid bubbles

The synovial fluid is a viscous liquid inside some of our joints, like the knee. It’s made of water, lubricants, and dissolved gas molecules.(3)

It also reduces friction from everyday movement, keeping our joints and cartilage healthy.

Moving or stretching our joints can pull the dissolved gas molecules together. This forms a big bubble that causes a loud “pop” when it collapses, which in turn dissolves the gas in the liquid again.(4)

A perfect example of this would be when we crack our knuckles.

This happens to all of us to some degree. Some people experience it more often than others, but it’s not a cause of concern as long as it’s not painful.

It doesn’t cause osteoarthritis either!(5)

2. Rubbing of tendons on bony structures

There are many tendons and ligaments around the knee. They help us bend and straighten the joint, as well as keep it stable.

But sometimes they rub over the bony structures of the femur, causing clicking sounds.

For example, some people feel crepitus on the side of the knee while standing up or squatting. The iliotibial band rubbing on the femur may be causing that noise.

If it’s not associated with knee pain, don’t worry about it.

Change the position of your feet or hips and check if the noise changes. You might find a position that won’t make the side of your knee joint crack.

3. Kneecap gliding

There’s cartilage behind the kneecap that helps it glide on top of the femur. It’s there so you can smoothly bend or straighten your knee.

But one body is not exactly the same as the other. Some people may have a bigger kneecap or a cartilage that’s a little uneven.

These differences can make some knees louder than others, causing a fine grating sound while squatting, walking, or running.

Don’t let this sound stop you from doing those activities! As long as it’s painless, don’t worry about the noises.

How to stop knee cracking and popping?

If you don’t have pain or swelling, the crepitus doesn’t need treatment.

But as it can be bothersome to some people, a good way to reduce the noise is with exercise.

For example, if you have a sedentary lifestyle, do more exercise. This will strengthen the muscles on your legs and may help reduce the noise.

It would be best to do so with a personal trainer, but you can start with these exercises at home to stop the popping:

  • Chair squats.
  • Glute bridges.
  • Deadlifts without weight.
  • Side steps.
  • Walk more often.

If you’re already active, you may need a physical therapist. We can help you identify movement patterns that could be causing your knee noise. And, of course, we will also give you specific exercises to manage it.

What if it hurts when my knees crack?

This is a sign that you need some medical attention.

Treatment will depend on the cause of the pain. A doctor or physical therapist can help you pinpoint the root cause and help you treat it.

Here are some common treatments for pain with knee popping:

Physical therapy

Physical therapy can help you by:

  • Reducing the pain on the joint.
  • Aid the healing of the tissue.
  • Strengthening your muscles without worsening the symptoms.
  • Giving you a plan to return to your activities as soon as possible.

Lose some weight if your BMI is above 25

Some people feel fewer noises after losing some weight.

This can also help you keep good health and prevent developing knee osteoarthritis in the future.(6)

Other options

You could try some over-the-counter medications. These should help you manage the pain associated with knee crepitus.

Also, applying heat or ice on top of the kneecap can help you with pain.

People with severe pain and loss of joint function may need surgery. Go check with an orthopedic surgeon if this applies to you.

When to see a doctor?

If you have pain related to the sounds, please seek medical advice.

Here are some common things that could be happening with your knee that need medical attention:

A meniscus or ligament tear

This is common in people playing sports that involve sudden changes of direction. Soccer, basketball, and tennis are a few good examples.

The meniscus is a shock-absorber disc inside the knee joint. It also protects your bones so they don’t rub together.

Conversely, a ligament is a strong, thick band that helps stabilize the joints.

If you’ve torn any of them during a sports activity or your daily life, you might feel:

  • A cracking or popping that wasn’t there before.
  • A loud pop at the moment of injury.
  • Pain, swelling, difficulty walking.

Knee osteoarthritis

This is the wear and tear of the soft tissue that protects the knee joint. It can cause pain, loss of range of motion, and muscle weakness.

This can develop with age, but being active throughout your life and keeping your BMI <25 can help prevent it.(6)

Crepitus following surgery

If the noises appeared after a knee replacement or surgery, make an appointment with your orthopedic surgeon as soon as possible.

There could be a problem with the artificial joint.

FAQs:

Is it normal for knees to crack all the time?

Knee popping is very common in healthy knees. It can be loud and annoying to some people, but if you don’t have knee pain, it’s not a cause of concern.

Are cracking knees a sign of osteoarthritis?

Not on its own.

It can be a sign of knee osteoarthritis if it’s associated with at least 2 of the following(7,8):

  • Knee pain in most days for the last month, that gets better with rest.
  • Loss of range of motion.
  • Morning stiffness on the knee.
  • +50 years old.

If so, go to a doctor and physical therapist to plan your treatment.

How to keep healthy knees?

Do regular exercise to strengthen your leg muscles – they’ll protect your knees from wear and tear.

Try to do strength training at least twice a week, take the stairs often, and prioritize walking instead of taking your car or public transport.(9)

Also, keep your BMI at 25 or lower. Being overweight or obese increases the risk of developing knee osteoarthritis.(6)

Conclusion: Why do my knees crackle?

Most people find the crepitus alarming and worrying, but it’s normal in most healthy knees.

As long as it didn’t start after an injury or if you don’t have any other symptoms, don’t worry about the crepitus.

See a doctor if the crepitus is getting painful, if your joint is swelling, or if it started after an injury.

References

  1. McCoy, G F et al. “Vibration arthrography as a diagnostic aid in diseases of the knee. A preliminary report.” The Journal of bone and joint surgery. British volume vol. 69,2 (1987): 288-93. doi:10.1302/0301-620X.69B2.3818762
  2. Song, Sang Jun et al. “Noise around the Knee.” Clinics in orthopedic surgery vol. 10,1 (2018): 1-8. doi:10.4055/cios.2018.10.1.1
  3. “Synovial Fluid.” Science Direct. Retrieved on June 5, 2021 from: https://www.sciencedirect.com/topics/medicine-and-dentistry/synovial-fluid
  4. Kawchuk, Gregory N et al. “Real-time visualization of joint cavitation.” PloS one vol. 10,4 e0119470. 15 Apr. 2015, doi:10.1371/journal.pone.0119470
  5. Unger, D L. “Does knuckle cracking lead to arthritis of the fingers?.” Arthritis and rheumatism vol. 41,5 (1998): 949-50. doi:10.1002/1529-0131(199805)41:5<949::AID-ART36>3.0.CO;2-3
  6. Raud, Benjamin et al. “Level of obesity is directly associated with the clinical and functional consequences of knee osteoarthritis.” Scientific reports vol. 10,1 3601. 27 Feb. 2020, doi:10.1038/s41598-020-60587-1
  7. Lespasio, Michelle J et al. “Knee Osteoarthritis: A Primer.” The Permanente journal vol. 21 (2017): 16-183. doi:10.7812/TPP/16-183
  8. Hunter, David J et al. “The symptoms of osteoarthritis and the genesis of pain.” Rheumatic diseases clinics of North America vol. 34,3 (2008): 623-43. doi:10.1016/j.rdc.2008.05.004
  9. “How much physical activity do adults need?” [Last reviewed: October 7, 2020]. Centers for Disease Control and Prevention. Retrieved on June 5, 2021  from: https://www.cdc.gov/physicalactivity/basics/adults/index.htm