41% of all people have noisy knees, and most of them are fine

THE 30-SECOND VERSION

That cracking sound in your knee is almost certainly not arthritis, not damage, and not something to fear. A review of 103 studies found 41% of all people have noisy knees. Below: the myth, the facts, and a look back at this week’s knee issue.

FEEL-GOOD FRIDAY · OCTOBER 30, 2026

Your Noisy Knees Are Probably Fine

A doctor cracked one hand for fifty years to prove it. A review of 36,439 people backs him up.

Carol and I were walking up the steps of a restaurant in Portland last spring when my left knee let out a pop so loud the couple behind us turned around. Carol laughed. I froze. Then I spent the next forty minutes at dinner wondering if my knee was falling apart.

I am not alone. A big review published in the British Journal of Sports Medicine in 2024 looked at 103 studies and more than 36,000 people. The result: about 41% of the general population has noisy knees. Crackling, popping, grinding. The medical word is crepitus, which just means a sound or feeling when the joint moves. And 36% of people with no pain and no knee injury had it too.

So what makes the sound? The best guess is gas. Your knee sits in a bath of synovial fluid, the natural oil we talked about on Tuesday. That fluid holds dissolved gases, mostly carbon dioxide. When you bend or straighten the knee, pressure inside the joint shifts. Small gas bubbles form and collapse. Pop. That is the sound.

It is the same thing that happens when someone cracks their knuckles. Which brings us to Dr. Donald Unger.

Unger was a California doctor whose mother warned him that cracking his knuckles would give him arthritis. He did not believe her. So he ran the longest one-man experiment in medicine. For fifty years, he cracked the knuckles of his left hand at least twice a day. He left his right hand alone. At the end, he compared both hands. No arthritis in either hand, and no apparent differences between the two. He published the result in Arthritis & Rheumatism in 1998, and in 2009 he won the Ig Nobel Prize in Medicine for it. The takeaway is simple. The pop is gas, not bone. It is not wearing your joints down.

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About 50 years

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MYTH VS. FACT

Cracking Knees Do Not Cause Arthritis

The fear is common. You stand up from a chair. Both knees pop. And a voice in your head says, “That can’t be good.” But the large 2024 review of 103 studies found something worth knowing: 36% of people with zero pain and zero injury history had knee crepitus. In other words, noisy knees are the norm for a huge share of the population, not a warning sign.

A separate study by Dr. Grace Lo and her team at Baylor College of Medicine followed 3,495 older adults with a mean age of 61 over four years. Nearly two-thirds of the people who reported “always” having knee crepitus did not develop symptomatic osteoarthritis during that time. That does not mean crepitus never matters. If you also have pain, swelling, or stiffness, get it checked. But the sound alone is not a diagnosis.

Here is the part I wish someone had told me on those restaurant steps. The pop is gas leaving solution in the fluid around your joint. It is the same thing as bubbles in a can of soda when you crack the tab. It sounds loud. It feels odd. But it is not bone scraping on bone, and it is not wearing anything down.

When the Sound Does Matter

There is a difference between a painless pop and a grinding feeling that comes with aching or swelling. Painless pops and cracks are almost always harmless gas bubbles. But if the sound comes with pain that lasts, swelling that stays, or a knee that locks or gives way, that is worth a visit to your doctor. The sound is not the problem. The pain is the problem.

A Reader’s Knee Win This Week

“Walt, I tried the warm towel on my knee before getting out of bed in the morning, like you wrote about on Wednesday. My husband asked me why I was heating up a towel in the microwave at 6 a.m. I told him it was cheaper than a new knee. By the time I got to the kitchen, the stiffness was half of what it usually is. Thank you.” Janet, 68, Ohio

I like Janet’s approach. A damp towel, thirty seconds in the microwave, fifteen minutes on a stiff knee. No prescription. No co-pay. And it lines up with what the 2019 ACR/Arthritis Foundation guideline says: both heat and cold are conditionally recommended for knee osteoarthritis.

This Week in Review

On Tuesday we looked at how knee cartilage feeds itself. It has no blood supply. It soaks up synovial fluid when you move and squeezes it out when you bear weight. That squeeze-and-soak cycle is why sitting too long makes knees stiff, and why a short walk clears the stiffness fast. On Wednesday we covered heat and cold. Short version: stiff and achy means heat, swollen and warm means cold. A damp warm towel before you move, an ice pack wrapped in cloth after you move. And today, the myth: the cracking sound is gas in the joint, not damage. Keep moving. Your knees are tougher than they sound.

⚠ WHEN TO STOP

When to stop and call your doctor

These are uncommon, but they’re signals to get checked promptly rather than push through:

● A knee that suddenly swells up hot and red, which could signal infection or gout

● A knee that locks in place or gives way without warning

● Pain shooting down a leg, numbness between the legs, or loss of bladder or bowel control

When in doubt, get it checked. PainFree complements your doctor’s care, it never replaces it.

THIS WEEK’S QUICK WINS

Three small things for your knees this weekend

🦿 Stop Worrying About the Pop

Next time your knee cracks when you stand, let it go. If there is no pain and no swelling, that pop is gas leaving the joint fluid. It is not damage. Keep moving.

0 minutes • Just a mindset shift

♨ Warm Towel Before You Rise

Wet a hand towel, microwave it for 30 seconds, test the temperature, and drape it over your stiff knee for 15 minutes before you stand. Heat loosens the joint and makes the fluid flow easier.

15 minutes • Best before your first steps

🚶 Five-Minute Walk After Sitting

Every time you have been seated for 30 minutes, stand and walk for five. This restarts the squeeze-and-soak cycle in your cartilage, pumping fresh fluid where it needs to go.

5 minutes • Your cartilage will thank you

RESEARCH BRIEF

Walking Beats Every Other Exercise for Knee Pain

A 2025 review published in The BMJ pulled together 217 randomized trials and 15,684 people with knee osteoarthritis. The researchers compared aerobic exercise (walking, cycling, swimming), strength training, mind-body work, and mixed programs. Aerobic exercise came out on top for pain relief at four and twelve weeks, and for mobility at four weeks, twelve weeks, and six months. Strength training helped too, but not as much. The authors concluded that aerobic exercise should be the first-line treatment for knee osteoarthritis. All forms of exercise were found to be safe. No type caused more injuries than the control groups.

217

Randomized trials reviewed

15,684

People with knee osteoarthritis studied

Aerobic exercise ranked first for pain relief at four and twelve weeks

Walking is free, needs no equipment, and works better for knee pain than any other exercise type tested. If you can walk, walk.

WORTH KNOWING

365 million

That is the estimated number of people worldwide living with knee osteoarthritis, according to the World Health Organization. Of all osteoarthritis cases, the knee is the most commonly affected joint, and about 73% of people living with OA are older than 55.

You are not alone in this. Not even close.

That is it for Knee Week. Next week we move on. For now, the short version: your cartilage feeds itself when you move, heat loosens a stiff joint, cold calms a swollen one, and that cracking sound is just gas.

I am not a doctor. I am a retired numbers guy who reads the studies and tests things on himself. Talk to your doctor before changing anything. But do not let a noisy knee scare you out of a walk. The walk is the medicine.

Here’s to quieter worries and louder living,
Walt

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