How To Move Without Pain

Why does my knee make a crunching sound?

by Meghan Griech, PT, DPT, cert MDT, CKTP

This article takes 6 minutes to read

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Knees can often make crunching sounds, kinda like stepping on dry leaves or breaking chips. It’s not unusual to hear cracks, pops, or crunches from knees, especially when getting up from a chair, walking downstairs, or getting out of the car. The noise we hear is called crepitus, and can happen at any joint; but the knees, ankles, and fingers are most common. The crunching noise can also sometimes be felt by putting your hand over your knee.

Understanding the Knee

Understanding knee crepitus will be better understood with a little background information on the knee. Three bones make up the knee joint, the femur (thighbone), tibia (shinbone), and patella (kneecap).  The kneecap rests in a valley of the femur bone called the trochlea groove. When the knee moves, the patellar moves up or down within this groove. The patella is surrounded by tissue that provides padding and helps the knee cap stay within the groove.

Between the femur and tibia is a cartilaginous tissue called menisci. There is an inner larger meniscus and a smaller outer meniscus, each meant to cushion the joints and help the bones slide easily as you move. 

The underside of the kneecap also has a lining of cartilage. This cartilage “rubs” against the end of the femur in the trochlear area. With normal wear, it can sometimes start to cause grinding and crepitus.

Knee crepitus can happen at any age, yet it does become more frequent as we age. Crepitus is often harmless, but if it happens after a trauma or if there is pain and swelling this could be a sign that you have an injury. Some normal (and harmless) reasons crepitus occurs is due to a natural process of air bubbles developing in the joint, and popping (think cracking your knuckles). 

This sound is usually a “Cracking” or “popping” sound.  Another cause for crepitus is when tendons or ligaments rub and snap over the bony structures in the knee.  This usually is also harmless, and unless you develop pain with this sensation you can usually ignore it.  Unfortunately, some crepitus is associated with knee injuries such as patellofemoral pain syndrome (PFS), torn cartilage, or osteoarthritis (OA).

Causes of Crepitus


Air Bubbles

Most joints, including the knee, are surrounded by a joint capsule and filled with fluid to help lubricate the joint.  The inside of this capsule needs to maintain constant pressure, but sometimes this can change with movement.  To compensate for changes in fluid volume, the body forms tiny air bubbles to compensate.  When the joint moves and puts pressure on the tissues the bubbles can ‘burst’, making a popping or cracking sound. 

Injury to Tissue around the Knee

Soft tissues around joints can swell if damaged or irritated. This could be due to a fall or unexpected injury, like a twisting force.  If there is pain or changes in how the joint moves, like a catching sensation, it can be from an injury to the meniscus, scar tissue or a tendon is moving over a protruding bone within the joint. 

Wear and Tear

When the pressure between the kneecap and the femur is greater than usual, the cartilage in the joint can start to soften and wear away. This can happen with age but also with changes or increases in activity.  This is often described as a “rubbing” sensation.

Torn Cartilage

Cartilage within the knee can tear over time, during twisting motions within the knee, or pivoting motions. A torn cartilage can cause swelling, stiffness, and difficulty moving the knee. When the meniscus tears, it can feel like a popping sensation according to the American Academy of Orthopedic Surgeons. Often people report a “catching” or even “locking” sensation in the knee.

Osteoarthritis of the knee

As osteoarthritis (OA) in the knee progresses, the cartilage that covers the ends of the bones gradually wears away.  As the bones rub on this increasingly rough surface, it can result in pain and mobility issues. According to a study, women aged 45 to 60 years who had both crepitus and patellofemoral pain had a 72 percent chance of developing OA, although they did not yet have a diagnosis of OA.

Looking for tips to treat your knee pain or osteoarthritis, read this article. 

When to worry about Crepitus

Crepitus in the knee is common and usually painless. However, if there is pain associated with the crackling and popping sounds, this could indicate a problem. Treatment will depend on the underlying cause of the pain and is a reason to seek medical attention to rule out possible infection, fracture, or joint injury. 

*Disclaimer: All information in this article is intended for instruction and informational purposes. The author(s) are not responsible for any harm or injury that may result.  This information is used to supplement not replace any advice you were provided from your doctor or another medical health professional.  No guarantees of specific results are expressly made or implied with this article.

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holding knee due to pain with walking down stairs