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  • The sound of joints “popping” comes from a gas-filled cavity (i.e. bubble) forming in your joint
  • When you “crack” your knuckles it expands the space between your bones, creating negative pressure that draws synovial fluid into the new gap
  • This influx of synovial fluid is what causes the popping sound and feeling when you crack a knuckle

Why Do Your Joints Crack?

May 02, 2015 | 293,484 views

By Dr. Mercola

In the 1970s, research was published showing that the sound your joints make when “cracked” is due to the popping of bubbles in the fluid between the joint.1 New research published in PLOS One suggests this long-held theory may be wrong.

The researchers used MRI video, which you can see above, to determine why joints make a popping sound when they crack. Rather than being caused by bubbles popping, they believe the sound comes from a gas-filled cavity (i.e. bubble) forming.

Lead study author Greg Kawchuk, a professor in the Faculty of Rehabilitation Medicine at the University of Alberta, said:

“It’s a little bit like forming a vacuum… As the joint surfaces suddenly separate, there is no more fluid available to fill the increasing joint volume, so a cavity is created and that event is what’s associated with the sound.”

Ironically, this was a theory originally proposed in the 1940s, which was later abandoned in favor of the bubble-popping theory. Another similar explanation suggests that when you “crack” your knuckles, or any other joint, it expands the space between your bones, creating negative pressure that draws synovial fluid into the new gap.

This influx of synovial fluid is what causes the popping sound and feeling when you crack a knuckle.2

Cracking Your Knuckles Is Not Likely to Lead to Arthritis

Your joints, including those in your knuckles, are surrounded by a membrane called the synovial membrane, which forms a capsule around the ends of your bones. Inside this membrane is synovial fluid, which acts as a lubricant and shock absorber so your bones don’t grind together when you move.

If you have osteoarthritis, the cartilage within your joints is progressively being damaged, and the synovial fluid is typically reduced as well. The pain and joint stiffness that you feel is a result of your bones starting to come into contact with each other as cartilage and synovial fluid diminishes.

It’s often thought that cracking your joints would be dangerous for people with osteoarthritis, or perhaps could even lead to this degenerative conditions. If you continually crack your knuckles, the synovial membrane and the surrounding ligaments will loosen, making it easier and easier for your joints to crack.

However, to date research has not shown a correlation between knuckle cracking and osteoarthritis in your hands. In one study of more than 200 people, the prevalence of osteoarthritis in any joint was similar among those who cracked knuckles and those who did not.3 The same held true when specific joint types were examined. The authors stated:

"Total past duration (in years) and volume (daily frequency x years) of knuckle-cracking (KC) of each joint type also was not significantly correlated with OA [osteoarthritis] at the respective joint. A history of habitual KC - including the total duration and total cumulative exposure 'does not seem to be a risk factor for hand OA.'"

Is Cracking Your Knuckles Safe?

In many cases cracking your knuckles becomes a habit that can be difficult to break. One study even suggested that the movement offers a sort of “therapeutic release,” and chronic knuckle crackers may come to regard the habit as a form of stress relief.

Personally, however, I don’t think it’s wise to crack your joints on a regular basis, and research suggests it could have some significant repercussions. More than 20 years ago, I co-authored a paper titled “Cracking Down on 'Neck Cracking,” which was published in the journal American Family Physician.4 In it, I argued that self-manipulation may lead to lax ligaments.

There are, in fact, reports in the literature of various injuries that have occurred from knuckle cracking, including overstretching of ligaments in the fingers, dislocated fingers, and a partially torn ligament in the thumb.5

Further, habitual knuckle crackers are more likely to have hand swelling and lower grip strength that may ultimately result in functional hand impairment.6 The damage was likely the result of the repeated stretching and loosening of the ligaments during repeated knuckle cracking.

There is also at least one reported case of knuckle pads in a teenaged girl who reported frequently cracking her knuckles daily. Knuckle pads are firm nodules that sometimes form over certain joints in your fingers.

They’re often associated with repetitive trauma or movement, and while they don’t cause physical symptoms, they can have psychological and cosmetic effects. In the girl’s case, the nodules slowly enlarged over the course of several years, and cracking of the knuckles was listed as the possible cause.7

Another Popping Noise Could Be Your Tendons Snapping

It’s estimated that between 25 percent and 54 percent of Americans crack their joints intentionally (with men doing it more often than women).8 However, if you’re not in the habit of cracking your joints and you still hear an unusual popping sound, it might not be due to your joints cracking at all.

Such noises may also come from your tendons, which keep your muscles attached to your bones, and ligaments, which connect your bones. As explained by Medical News Today:9

Doctors believe that tendons can make a popping noise when they quickly snap over a joint. Ligaments may make popping noises when they get tight while the joint is moving. When a joint moves, the tendon's position with respect to the joint is forced to change.

It is not uncommon for a tendon to shift to a slightly different position, followed by a sudden snap as the tendon returns to its original location with respect to the joint. These noises are often heard in the knee and ankle joints when standing up from a seated position or when walking up or down the stairs.”

Also, joint cracking shouldn’t be confused with crepitus, which is the grinding or clicking sound that occurs when a joint with worn cartilage moves.

Do You Want to Stop Cracking Your Knuckles?

While cracking your knuckles is unlikely to lead to arthritis, it does appear to increase inflammation and lower grip strength in your hands over time. There is also a possibility that it could cause injury or damage to your joints and ligaments over time. Still, when you crack your knuckles, the joints become looser and have more mobility for a short period afterward.

This loose feeling is pleasurable for some people and can make it hard to quit the habit cold. If you crack your knuckles and find it difficult to stop, I suggest you to try the Emotional Freedom Technique (EFT). EFT is a powerful self-help method that is very effective for regular stress management as well as for breaking all kinds of addictions, including knuckle cracking. Once the emotional distress is reduced or removed, your body can often rebalance itself and accelerate healing.

Specifically, EFT is a form of psychological acupressure, based on the same energy meridians used in traditional acupuncture to treat physical and emotional ailments for over five thousand years, but without the invasiveness of needles. Instead, simple tapping with your fingertips is used to input kinetic energy onto specific meridians on your head and chest while you think about your specific problem -- whether it is a traumatic event, an addiction, pain, etc. – and voice positive affirmations.

This combination of tapping the energy meridians and voicing positive affirmation works to clear the "short-circuit" — the emotional block — from your body's bioenergy system, thus restoring your mind and body's balance, which is essential for optimal emotional health and the healing of physical disease. For a demonstration of how to perform EFT, please view the video below featuring EFT practitioner Julie Schiffman. This is a general demonstration that can be tailored to just about any problem. You can also find text instructions and photographs of where to tap on my EFT page.

Exercise Can Make Your Joints Feel Great

Do you crack your joints because they’re stiff and you’re looking for relief? A better option may be exercise, which can significantly improve joint function and even lessen joint pain. The notion that exercise is detrimental to your joints is a serious misconception, as there is no evidence to support this belief. It's simply a myth that you can “wear down” your knees, for instance, just from average levels of exercise and/or normal activity. Instead, the evidence points to exercise having a positive impact on joint tissues, whether you need to lose weight or not.

Exercise, along with a healthy diet, can also help you to jumpstart weight loss if you're overweight, and this can lead to tremendous improvements in your joint pain and function. For instance, a JAMA study revealed that among overweight and obese adults with knee osteoarthritis, following an intensive diet and exercise program led to less pain and better function, along with better physical health-related qualify of life scores.10 So if you’re struggling with stiff joints, and turning to popping them as a form of “treatment,” try a regular exercise program instead. As NPR reported:11

“Pretty much any type of exercise seems to reduce pain and increase flexibility [in joints], according to [rheumatologist Dr. David] Felson. 'There have been a variety of different exercise studies which have tried everything from water aerobics to walking to muscle strengthening, and they all seem to work.'”

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