Many of us have noisy joints. Knees crack on the stairs, necks pop when we stretch, and knuckles seem to crack almost on demand. These sounds can be startling and are often blamed on ageing, damage or the looming threat of arthritis.
As a physiotherapist and researcher of chronic joint pain, I am frequently asked whether joint noises are something to worry about. The reassuring answer is that, in most cases, they are not.
One reason joint sounds cause anxiety is that we tend to treat them as a single phenomenon. Clinically, they are not.
The familiar “crack” from knuckles, backs or necks is usually caused by a process called cavitation. Joints are surrounded by a capsule filled with synovial fluid, a thick lubricant that contains dissolved gases such as oxygen, nitrogen and carbon dioxide. When a joint is stretched beyond its usual range, pressure inside the capsule drops. A gas bubble forms and collapses, producing the popping sound.
This is why you cannot crack the same joint repeatedly. It typically takes around 20 minutes for the gas to dissolve back into the fluid.
Other noises are different. Snapping sounds often come from tendons moving over bony structures. Grinding, crunching or creaking noises, known as crepitus, are particularly common in the knees. These are thought to arise from movement between cartilage and bone surfaces and are often felt as well as heard.
Knees are especially prone to crepitus because of how they work. The kneecap sits in a groove at the front of the thigh bone and is guided by muscles above and below it. If those muscles pull unevenly, because of strength imbalances, tightness or foot and hip mechanics, the kneecap can track slightly off centre. This can increase the crunching or grinding sensation.
Noise on its own is rarely a problem. What matters clinically is whether it comes with other symptoms. Pain, swelling, locking of the joint or a noticeable reduction in function are the things that warrant further assessment.
Does cracking joints cause arthritis?
There is no strong evidence that cracking or popping joints causes osteoarthritis.
Research in this area is challenging, as it requires following people over many years and accurately tracking their habits. The studies that do exist, including retrospective and cross-sectional research, have not found a meaningful link between habitual joint cracking and arthritis.
Some studies have explored other outcomes, such as grip strength or joint laxity, which refers to how loose or flexible a joint is and how much it can move beyond its typical range. Findings have been mixed and inconsistent. Overall, there is no convincing evidence that cracking joints causes damage to joint structures, strength or long-term joint health.
Many people report that joint cracking feels satisfying or relieving. This makes sense. Stretching a joint to the point of cavitation can temporarily increase range of motion and reduce muscle tension. There is also a neurological effect, as nerve endings are stimulated during the movement, sending a reflex signal to the brain which causes local muscle relaxation in the area. The audible pop itself can provide a calming, satisfying sensation which may lead to developing that habitual self-soothing mechanism for tension that annoys your family members and friends.
The key point is that these effects are short lived. Joint cracking does not fix underlying mechanical issues or provide lasting improvements in mobility. If relief only comes from repeated cracking, the underlying cause has not been addressed.
Spinal manipulation
Spinal manipulation, whether performed by physiotherapists, chiropractors or other practitioners, relies on the same cavitation mechanism. There is evidence that it can provide short-term pain relief and reduce muscle tension for some people.
However, it is important to be cautious, particularly with the neck. The cervical spine protects the spinal cord and major blood vessels supplying the brain. Rare but serious complications, including stroke, have been reported following neck manipulation. Anyone considering this type of treatment should ensure it is carried out by a properly trained professional and understand that it targets symptoms rather than underlying causes.
Joint noises do tend to become more common with age. Cartilage changes over time, and muscles and ligaments may lose some of their strength and elasticity. These changes can increase the likelihood of noise during movement.
People who have joint conditions such as knee osteoarthritis and have noisy joints tend to report slightly more pain and reduced function compared to people with osteoarthritis and no crepitus. It may be reassuring to know that there is no difference in tests like walking speed or muscle strength between groups, pointing to a potential psychological impact of noisy knees.
Crucially, noise alone is not a reason to stop being active. Some people reduce their physical activity because they fear they are “wearing out” their joints. In fact, the opposite is true. Movement is essential for joint health. Cartilage relies on regular compression and release to receive nutrients, as it has very limited blood supply.
Exercise is a cornerstone of joint health and is recommended as the first treatment to try in national and international clinical guidelines for conditions such as osteoarthritis. Consistency matters more than the specific type of exercise. The best exercise is the one you will keep doing.
There is no evidence that supplements such as collagen or fish oils reduce joint noise. Large studies show limited effects on pain and function at a population level, although some people report benefits. These supplements are generally safe, but if they do not help, they are unlikely to be worth the cost.
Joint noises are usually harmless. They are worth assessing if they are accompanied by pain, swelling, locking, or reduced function, or if they are limiting your confidence to move. Staying active is one of the best things you can do for your joints, whether they crack, pop, crunch or stay silent.
Strange Health is hosted by Katie Edwards and Dan Baumgardt. The executive producer is Gemma Ware, with video and sound editing for this episode by Sikander Khan. Artwork by Alice Mason.
In this episode, Dan and Katie talk about a social media clip from loryalien via TikTok.
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