If your knees sometimes sound like the name of a popular breakfast cereal, you’ve experienced something known as crepitus. That snap, crackle, and pop coming from your knees can be alarming, but it’s typically not cause for concern. It’s a common phenomenon that occurs in joints all over the body. 

“Unless you had a recent trauma, like a fall, crepitus is usually harmless,” says Caitlin Shaw, PT, DPT, a physical therapist with Hinge Health. 

And while the cracking sounds your knee makes might give you pause, it’s not a reason to fear movement or using your knee for exercise or activities. “Many people are distressed by noises in their knees — they think something’s torn or broken,” says Dr. Shaw. One study found that when people believed that the noise in their knee was dangerous or damaging to the joint, they tended to alter movements to avoid the noise or stopped activities that caused crepitus. 

If you have knee pain or discomfort coupled with the noise, exercise can help to reduce that as well.

Read on to learn more about knee crepitus: what it is, what causes it, and how to keep your knees silent, strong, and resilient to pain with tips and exercises from our Hinge Health physical therapists.

What Is Knee Crepitus?

Knee crepitus is the sound of popping, crackling, crunching, or grinding that occurs when moving the joint. Crepitus can affect any joint and can occur at any age, but it becomes more common as you get older.

The sound may be muffled or it may be loud enough for other people to hear. “When some people do a squat, they say, ‘You’re going to hear my knee,’” says Dr. Shaw. “They know it happens and have become accustomed to it.”

Causes of Popping Knees

Many factors can contribute to knee crepitus, including:

• Air bubbles. Changes in joint pressure can cause tiny bubbles of gas to slowly form in the synovial fluid, a thick liquid that lubricates joints. “It’s the same thing that happens when you crack your knuckles,” says Dr. Shaw. “Not many people crack their knees as a repetitive motion, though, so they get nervous that something’s wrong even though it’s pretty benign.” 

• Ligaments or tendons. The tendons and ligaments in your knee joint, both of which play a role in keeping the knee flexible and resilient, may snap into place (much like a rubber band) during motion, and this can create a sound.

• Patellofemoral pain syndrome (PFPS). PFPS is a general term that refers to pain in the knee, usually at the front and center, due to the wearing of cartilage over time. It can occur when the kneecap (patella) is out of alignment or due to repetitive motion without doing strengthening exercises to prepare your knee for those activities. While PFPS is often referred to as “runner’s knee,” it can also affect non-athletes at any age.  

• Cartilage tear. Crepitus can also be a symptom of a torn meniscus, the rubbery knee cartilage that acts like a shock absorber between the shin bone and the thigh bone. In this case, the popping sensation may be accompanied by swelling and stiffness. 

• Conditions like osteoarthritis. The crackling noise can be a sign of osteoarthritis (OA). With OA of the knee, the cartilage that covers the ends of the bones (and allows them to slide over each other without friction) wears away over time. As the surfaces inside the joint no longer glide smoothly, noise — and often pain — can occur. In one study, 75% of people who developed knee OA reported crepitus in or around their knee joint in the year leading up to developing symptoms.

When Should I Be Worried About Popping Knees?

Practically all knees make what doctors call “physiological noise,” which means the noise has no connection to pain or function. Sometimes, though, crepitus may signal something more serious (called “pathological noise”). That would be the case if, for instance, the noise is accompanied by sharp pain or swelling, or if you’re experiencing other mechanical changes, like your knee is locking or giving out. 

“If you’re having progressive weakness or experiencing locking sensations where you can’t get your knee unstuck from a position, then it would be wise to talk to your doctor to gain a better understanding of what’s going on,” says Dr. Shaw.

Tips to Prevent Popping Knees

Noisy knees become more common with age. Help keep your knees strong, injury-free, and quiet by adopting these healthy habits.

• Stay active. Your joints thrive on movement, which helps keep them well-lubricated (think of it like applying WD-40 to a creaky door hinge). The more you can move, the better. Even if you've been diagnosed with a condition like arthritis, activities such as walking can be extremely helpful.

• Stabilize your knees. Strengthening the muscles in your legs and butt (glutes) will keep your knees from shifting sideways when you move. 

• Remain flexible. “Stretching throughout the day and doing a dynamic warm-up before you exercise can help prevent some popping, as it stretches the muscles and tissues around the joint,” says Dr. Shaw. 

• Maintain a healthy weight. Sticking close to your ideal weight helps decrease the amount of pressure on the knee joint, minimizing damage. Every pound of body weight you lose results in four pounds of pressure being lifted from your knees.

While no exercises directly target crepitus, these moves will help treat the underlying cause by improving joint alignment and joint health, says Dr. Shaw. So, in addition to making your knees less noisy (or keep them from getting louder), you’ll build strength and flexibility in your knees to reduce and prevent pain.

The information contained in these videos is intended to be used for educational purposes only and does not constitute medical advice or treatment for any specific condition. Hinge Health is not your healthcare provider and is not responsible for any injury sustained or exacerbated by your use of or participation in these exercises. Please consult with your healthcare provider with any questions you may have about your medical condition or treatment.

PT Tip: Swim Into Action

“For those who are struggling to get or stay active due to unacceptable levels of pain, aquatic therapy may help you get stronger, maintain a healthy weight, and work back to tolerating activities like walking,” says Dr. Shaw. This is especially true if you have pain with your crepitus. Swimming takes the weight off the joint, which can help you stay active without discomfort. In addition to burning calories, swimming strengthens leg muscles, contributing to better knee health. It can be a great bridge to other important activities, like walking, hiking, and exercise therapy. 

How Hinge Health Can Help You

If you have joint or muscle pain that makes it hard to move, you can get the relief you’ve been looking for with Hinge Health’s online exercise therapy program. 

The best part: You don’t have to leave your home because our program is digital. That means you can easily get the care you need through our app, when and where it works for you.  

Through our program, you’ll have access to therapeutic exercises and stretches for your condition. 

Additionally, you’ll have a personal care team to guide, support, and tailor our program to you. See if you qualify for Hinge Health and confirm free coverage through your employer or benefit plan here.

This article and its contents are provided for educational and informational purposes only and do not constitute medical advice or professional services specific to you or your medical condition.

References

1. Knee Crepitus. (n.d.). Physiopedia. Retrieved from https://www.physio-pedia.com/Knee_Crepitus

2. Snap, Crackle & Pop: Why Do My Knees Make Noises—And Should I See A Doctor? (2022, March 24). Henry Ford Health. https://www.henryford.com/blog/2022/03/noisy-knees 

3. Why Does My Knee Crackle? NO DATE. New York Sports Medicine Institute. https://nysportsmedicineinstitute.com/why-does-my-knee-crackle/

4. Song, S. J., Park, C. H., Liang, H., & Kim, S. J. (2018). Noise around the Knee. Clinics in Orthopedic Surgery, 10(1), 1. doi:10.4055/cios.2018.10.1.1

5. Robertson, C. J., Hurley, M., & Jones, F. (2017). People’s beliefs about the meaning of crepitus in patellofemoral pain and the impact of these beliefs on their behaviour: A qualitative study. Musculoskeletal Science and Practice, 28, 59–64. doi:10.1016/j.msksp.2017.01.012

6. Why Do My Joints Make Noise ― Clicking and Popping? (2019, June 19). Cleveland Clinic. https://health.clevelandclinic.org/why-do-my-joints-make-noise-clicking-and-popping/

7. Lo, G. H., Strayhorn, M. T., Driban, J. B., Price, L. L., Eaton, C. B., & Mcalindon, T. E. (2017). Subjective Crepitus as a Risk Factor for Incident Symptomatic Knee Osteoarthritis: Data From the Osteoarthritis Initiative. Arthritis Care & Research, 70(1), 53–60. doi:10.1002/acr.23246

8. Horton, J. (Host). (2023, May 31). Snap! Crack! Pop! Why Your Joints Make Noise with Andrew Bang, DC [Audio podcast episode]. Health Essentials. Cleveland Clinic. https://my.clevelandclinic.org/podcasts/health-essentials/snap-crack-pop-why-your-joints-make-noise-with-andrew-bang-dc