Cracking, popping joints: should you worry, what to eat?

Research links the cracking and popping you hear from your joints to gas in the joint fluid. If there is no pain and no swelling, there is usually little reason to worry: the UK's NHS says painless clicking in the knee is normal, and a study of habitual knuckle crackers found no immediate harm after cracking. These sources do not link the sound to any particular food. What to watch for is noise that comes with pain, swelling, a joint that locks, or noise after an injury; those are reasons to see a doctor.

Many people hear these sounds when cracking their knuckles, turning their neck, getting up from a chair or squatting, and worry that something is wrong with their bones or that their body is missing something. This article brings together what is known about joint noises and how to tell normal sounds from ones a doctor should look at.

What makes joints crack and pop?

The crack usually does not come from the bone itself, but from what happens inside the joint.

Gas in the joint fluid

Joints are lubricated by synovial fluid. Kawchuk and colleagues explain that when the joint surfaces are pulled apart, they resist separation until a critical point and then separate rapidly, and the negative pressure this creates forms a gas cavity in the fluid. Cracking sounds have historically been attributed to the sudden collapse of such a bubble.

When exactly the sound happens is still being studied

The 2015 study by Kawchuk and colleagues in PLOS ONE used real-time MRI to film finger joints being pulled until they cracked. It found that the sound came with the rapid formation of a gas cavity as the joint separated, and that the cavity was still visible afterwards rather than collapsing. That differs from the older explanation that the sound comes from bubbles bursting. A 2018 review by Rizvi and colleagues says there is agreement that a bubble forms as part of knuckle cracking, but the process by which the bubble is formed and the source of the cracking sound is not clear. Both explanations agree that it involves gas in the joint fluid.

Why you can't crack it again straight away

Kawchuk and colleagues describe that after a joint cracks, it is in a refractory phase in which no further cracking can occur until time has passed, approximately 20 minutes. That is why the same joint will not crack again right after you have cracked it.

If it cracks but doesn't hurt, should I worry?

Mostly not. Several sources point the same way.

A note on cracking joints forcefully

Boutin and colleagues examined 400 finger joints in 40 people and found no immediate problems after cracking, but they note that the long-term outcomes of habitual knuckle cracking still need study. Not forcing, twisting or pulling joints hard is the easier choice.

Knees that crunch when you stand up or climb stairs

If your knees crunch when you get up from a squat or climb stairs and there is no pain, that fits with the NHS view that painless clicking is normal. If the noise comes with knee pain on the stairs, see Knees hurt on stairs at 50? How should you look after them?

My bones crack and pop. What should I eat?

This is a very common question, because many people assume joint noise is a sign that the body is short of something. The research above explains the sound through gas in the joint fluid, and does not link it to any particular food.

Eating from a variety of food groups and keeping an eye on your weight are basics of overall health.

What can I do in everyday life?

Keep moving

The NHS advises not to stop moving a painful joint completely, and to eat a healthy, balanced diet and exercise regularly.

• Get up and walk around regularly during screen work.
• Stretch gently after waking and before exercise.
• Set up your desk and chair so you can sit upright comfortably.

Warm up before exercise

The NHS advises that you warm up properly before exercising to prevent injury, and says its warm-up routine should take at least 6 minutes.

Avoid forceful cracking

If you crack your knuckles or neck out of habit, try slow stretches instead.

When should I see a doctor about noisy joints?

Book an appointment

• Joint pain stops you doing normal activities or affects your sleep (NHS)
• The pain or swelling is getting worse or keeps coming back (NHS)
• It has not improved after 2 weeks of home care (NHS)

Get advice right away

• Your knee locks, gives way or painfully clicks (NHS)
• Your knee is badly swollen or has changed shape (NHS)
• You have joint pain and the skin around it is swollen and feels hot (NHS)

Go to the emergency department straight away

• Very bad joint pain after a fall or injury (NHS)
• You cannot walk or put weight on the joint (NHS)

If you want to use a painkiller, ask a pharmacist or doctor first, and do not use any medicine on your own for long periods.