Joints can make a variety of sounds - playing a percussive symphony of popping, cracking, creaking, grinding, and snapping noises.
The joints that "crack" most often are the knuckles, knees, ankles, back, and neck. There are numerous reasons why these joints make noise, but, can knuckle-cracking cause or exacerbate arthritis?
For some, joint cracking is a nervous habit; for others the sensation brings relief. Depending on which research you read, between 25 and 54 percent of people crack their knuckles, with men more likely to do so than women.
Here, we will take a closer look at why joints crack, and if cracking them causes any medical issues.
Contents of this article:
Fast facts on knuckle cracking
Here are some key points about knuckle cracking. More detail and supporting information is in the main article.
- Joint cracking brings relief to some people, for others, it is a habitual act
- Usually, it takes 25-30 minutes to be able to crack knuckles again after cracking
- Movement from a joint with worn cartilage can make a grinding sound - called crepitus
Does cracking your joints/knuckles cause arthritis?
People tend to crack their joints in one of three ways: bending them backward or forward; turning them sideways; or pulling on the bones around the joint.
While any joint can be popped, it is the knuckles of the fingers that are most commonly popped.
Cracking the knuckles probably doesn't raise the risk of arthritis.
At least, that is the conclusion of several studies investigating the phenomenon.
Dr. Donald Unger
Between 25-54 percent of people crack their knuckles.
In 1998, Dr. Donald Unger published a letter entitled "Does knuckle cracking lead to arthritis of the fingers?" to the editors of Arthritis and Rheumatism, the world's premier rheumatology journal.
Dr. Unger reported that he had been cracking the knuckles of his left hand at least twice daily over a 50-year period, while the right hand was never cracked and used as a control.
The knuckles on the left were cracked at least 36,500 times, while those on the right cracked rarely and spontaneously.
Unger wrote, "During the author's childhood, various renowned authorities (his mother, several aunts, and his mother-in-law) informed him that cracking his knuckles would lead to arthritis of the fingers."
He went on to use a half-century "to test the accuracy of this hypothesis."
Finally, after five decades, Unger analyzed his data set: "There was no arthritis in either hand and no differences between the two hands." He concluded, "There is no apparent relationship between knuckle cracking and the subsequent development of arthritis of the fingers."
Uniformed Services University of the Health Sciences
Researchers at the Uniformed Services University of the Health Sciences decided to investigate the question of knuckle cracking's association with arthritis.
The researchers included 215 people in the study, 20 percent of whom popped their knuckles regularly. Of those knuckle crackers, 18.1 percent of them had arthritis in their hands, compared to 21.5 percent of the study participants who did not crack their knuckles.
The study showed that the chances of having arthritis are pretty much the same whether you crack your joints or not. However, arthritis is not the only concern for people who crack their joints.
Inflammation and weak grip
A large study in 1990, performed by the Department of Internal Medicine, Mount Carmel Mercy Hospital, in Detroit, focused on 300 participants over the age of 45, 74 of whom cracked their knuckles, 226 did not. Both groups showed similar rates of arthritis in their hands.
However, the 74 who cracked their joints showed a higher rate of inflammation of the hands and a weaker grip. So, while joint cracking may not cause arthritis, it can have a negative impact on the overall health and strength of hands.
Many highly respected medical facilities and sources, including Harvard and the Johns Hopkins Arthritis Center, agree that joint cracking does not cause arthritis. Habitual joint cracking does not correlate with arthritic changes but does correlate with loss of grip strength and soft-tissue swelling.
On the positive side, there is evidence of increased mobility in joints right after popping. When joints are manipulated, this stimulates the Golgi tendon organs (a set of nerve endings involved in the sense of motion), which then relaxes the muscles surrounding the joint.
This is part of the reason why people report feeling "loose" and invigorated after leaving the chiropractor's office, where cavitation (the formation of an empty space within a solid object or body) is induced as part of the treatment. The back, knees, elbows, and all other movable joints are subject to the same kind of manipulation as knuckles.
What causes cracking joints?
Joint cracking is a poorly understood phenomenon. The exact reason joints pop and snap is not known, although there are a few theories, which are discussed below.
Synovial fluid bubbles and cavitation
Cracking your knuckles does not cause arthritis.
When a finger or joint is extended, the pressure inside the finger is lowered and the gases that are present, such as carbon dioxide, are released in the form of a bubble.
This action creates a vacuum that the gases then fill. As the pressure of the synovial fluid drops, gasses dissolved in the fluid become less soluble, forming bubbles.
When joints are extended through pulling, there is a sudden and dramatic increase in surrounding pressure that causes a corresponding sudden partial or total collapse of these gas bubbles.
This rapid implosion, collapse, or bursting of the gas bubbles creates an audible popping sound. The bubbles pop when the bones are pulled apart, creating negative pressure.
It takes about 25-30 minutes for the released gases to dissolve back into the synovial joint fluid. During this period, the knuckles will not crack. This released gas increases the joint volume by 15-20 percent, with most of the gas (about 80 percent) consisting of carbon dioxide. Once the gas has dissolved once more, cavitation can reoccur, and the knuckles can be popped again.
Studies have also shown that there are two sound peaks during knuckle cracking, but the causes of these peaks remain unknown. It is likely that the first sound is related to the gas dissolving out of solution, while the second sound is caused by the capsule reaching its length limit.
The bubble collapse theory of joint popping has recently been debunked by Canadian researchers on the basis of visual evidence of what happens in the joint as it cracks.
By collecting real-time footage using magnetic resonance imaging (MRI), the researchers in Alberta, Canada, concluded that joint cracking is related to cavity formation rather than the collapse of gas bubbles.
The scientists studied ten metacarpophalangeal joints by inserting volunteers' fingers into a flexible tube that could be used to apply traction to the joint. They took images using MRI before and after traction and took 3.2 frames per second when traction was applied to the point of cracking.
The results showed the rapid creation of a cavity in the joint at the point of joint separation resulting in the production of sound. The cavity remained visible after the noise.
This research suggests that for joints to be cracked, there need not be existing gas bubbles. Instead, the cracking of the joint itself may be sufficient to cause rapid cavitation and the popping sound.
Tendons snapping over joints
Joint cracking is often confused with the snapping sound made by stiff tendons or other bands of soft tissue sliding between muscles or over bony outcrops.
Tendons keep muscles attached to bones and are like rubber bands stretched over the joints. Similarly, ligaments extend to connect bones to other bones. 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, this forces a change in the tendon's position relative to the joint. 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.
Shoulder joint pop, crack, or click
If there is no pain experienced with cracks or clicks, the soft tissue in a joint is identified as the cause. Noises that are associated with pain may indicate damage to the surfaces of the joint.
Such cracks and clicks may be due to tears in the labrum, a ring of cartilage that acts as a rubber seal around the shoulder joint. The labrum may snap over the other structures of the shoulder joint as the arm moves.
Sometimes the clicking may be due to the shoulder slipping in and out of joint. This is known as shoulder instability.
Do the cracking sounds need to be treated?
Whatever the cause of joint cracking and popping, the sounds themselves do not require specific treatment. There are no known long-term sequelae (chronic health issues) associated with these noises, and there is no basis for the warning to "not crack your knuckles because it can lead to arthritis."
There are also no supplements or exercises proven to prevent these noises.
Should you be worried about the cracking and popping of a joint?
For the most part, the cracking and popping of joints is normal and nothing to be concerned about.
The time to worry about cracking or popping a joint is when the sounds are accompanied by pain. Joint swelling is also abnormal and should be assessed by a doctor.
If the joint gets locked or stuck when it pops or cracks this may also indicate a joint problem and should be evaluated. If there is decreased motion of the joint, swelling, or a loss of joint function, it is important to seek medical advice and treatment.
Taking care of your joints
The most important thing to know about joint health is that prevention is better than treatment. Achieving and maintaining an appropriate body weight helps to lessen pressure on the joints and is best achieved by engaging in regular, low-impact exercise so as to minimize the risk of injury, while strengthening muscles to better support the joints and act as a shock absorber.
Individuals who enjoy cracking their knuckles should bear in the mind the conclusions of the doctors who carried out the research in the LA nursing home. They said: "The chief morbid consequence of knuckle cracking would appear to be its annoying effect on the observer."