Joints can make a variety of sounds - playing a percussive symphony of popping, cracking, creaking, grinding and snapping noises.
The joints that "crack" are often the knuckles, knees, ankles, back and neck. There are numerous reasons why these joints "sound off," but, can your knuckle-cracking habit cause or exacerbate arthritis? Is cracking your knuckles and joints just another harmless habit?1,2,7,24
For some, joint cracking is a nervous habit; for others the sensation brings relief. Depending on which research you read, between 25% and 54% of people crack their knuckles, with men more likely to do so than women.14-16 Let us take a closer look at joints, why they crack and if cracking them causes any medical issues.
Contents of this article:
You will also see introductions at the end of some sections to any recent developments that have been covered by MNT's news stories. Also look out for links to information about related conditions.
Fast facts on joint cracking
Here are some key points about joint 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.
- The interphalangeal and the metacarpophalangeal joints in the fingers are the easiest joints to crack.
- The "popping" sound is thought to be gas bubbles imploding and collapsing in the synovial fluid that surrounds the joints.
- Usually it takes 25-30 minutes to be able to crack knuckles again after cracking.
- X-rays show that gas bubbles remain present in the synovial fluid for up to 20 minutes after cracking.
- Cracking sounds can also be triggered by tendons snapping over a joint.
- Movement from a joint with worn cartilage can make a grinding sound - called crepitus.
- Joint cracking has not been shown to cause arthritis.
- People who crack their joints show a higher rate of inflammation of the hands and weaker grip.
Joints, knuckles and their uses
The joints are the parts of the body where the ends of two bones come together, with joints coming in several shapes, sizes and types:1,3
Between 25-54% of people crack their knuckles, with men more likely to do so than women.
Types of joints
- Pivot joints: allow rotary movement. For example, allowing side to side motion of the head, and the twisting movement of the forearm bones against the upper arm
- Hinge joints: a class of synovial joint that includes the ankle, elbow and knee joints. Hinge joints are formed between two or more bones where the bones can only move along one axis to flex or extend
- Ball-and-socket joints: a joint in which the rounded surface of a bone moves within a depression on another bone. Such joints allow greater freedom of movement than any other type of joint and are most highly developed in the large shoulder and hip joints
- Gliding joints: occur between the surfaces of two flat bones held together by ligaments. For example, some of the bones in the wrists and ankles move by gliding against each other
- Saddle joints: allow for two different types of movement. For example, a saddle joint allows your thumb to move toward and away from your forefinger as well as crossing over the palm of your hand toward your little finger
- Condyloid joints: similar to ball-and-socket joints, minus the socket. Instead, the "ball" simply rests against the end of the bone.
The ends of bones at these joints are covered with articular cartilage and surrounded by a "joint capsule" containing synovial fluid. It is this protective fluid that serves as a lubricant for the joint, cushioning the cartilage and tissues. Synovial fluid is also a source of nutrients for the cells that maintain the joint cartilage. Synovial fluid contains dissolved gasses such as oxygen, nitrogen and carbon dioxide.1,3,9
Why do people pop their joints?
Some people find joint cracking satisfying, experiencing a physical release, feeling of looseness and increased mobility for a short period after cracking the joint. Others crack their joints out of habit, in much the same way as people who twirl their hair or jiggle their foot up and down.
Whether you have cracked your knuckles for years, do it as a nervous habit, or hear the occasional pop or crack when working around the house - you are not alone in wondering what the cracking is and what it does to your joints.9
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.9
Cracking your knuckles does not cause arthritis.
Some people are repulsed by knuckle cracking, and parents often try to curtail the habit in their children, believing that cracking the knuckles can lead to arthritis later in life.7 Is this true, or is cracking the knuckles and popping the joints just a harmless habit that annoys some people?
Cracking your knuckles may aggravate the people around you, but it will probably not raise your risk for arthritis. At least, that is the conclusion of several studies that compared rates of hand arthritis among habitual knuckle crackers and those who do not crack their knuckles.2
One study found that there was no increase in hand arthritis among knuckle crackers. However, knuckle cracking was related to hand swelling and lower grip strength.3,4
Another study indicated that while knuckle cracking was not associated with arthritis, it was associated with dislocation of tendons and damage to ligaments that surround the joints. So, while cracking your knuckles is not thought to cause arthritis, it may lead to soft tissue injuries.3
Dr. Donald Unger
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.7
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.7
The knuckles on the left were cracked at least 36,500 times, while those on the right cracked rarely and spontaneously.8
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 apparent differences between the two hands." He concluded, "There is no apparent relationship between knuckle cracking and the subsequent development of arthritis of the fingers."
Fittingly, Dr. Unger was awarded the 2009 Ig Nobel Prize for Medicine. These awards are presented annually on the eve of the real Nobel Prizes by the organization Research for "achievements that first make people laugh, and then make them think."7
During the ceremony for accepting his award he let out a cry, "Mother, you were wrong!"10
Swezey and Swezey
Responding to the Unger paper, Dr. Robert Swezey, wrote to the journal to report that his 1975 study also found no case for the theory that knuckle cracking causes arthritis. The 28 participants of the study were residents in a Jewish nursing home in Los Angeles; they were asked whether they had ever cracked their knuckles habitually. Those who had cracked their knuckles were less likely to have osteoarthritis in their hands later on.
Swezey further consulted Rand Corporation statistician John Adams, who noted, "It appears that the [Unger] study was not blinded. Blinding would only be possible if the investigator didn't know left from right. This is not likely since studies indicate that only 31% of primary care physicians don't know left from right."7,8
Uniformed Services University of the Health Sciences
In a recent study, researchers at the Uniformed Services University of the Health Sciences decided to answer the question of knuckle cracking association with arthritis once and for all.9
The researchers included 214 people in the study, 20% of whom popped their knuckles regularly. Of those knuckle crackers, 18.1% of the had arthritis in their hands, compared to 21.5% 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
While joint popping may not cause arthritis, it is not completely risk-free. In at least one study, chronic joint popping was shown to cause inflammation and weakened grip in the hands.10
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, while 226 did not.10
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.10
The authors say this means knuckle cracking should be discouraged, but the study fails to address the question as to whether the people who cracked their knuckles may have felt more discomfort in their hands in the first place.
Many highly respected medical facilities and sources, including Harvard and the Johns Hopkins Arthritis Center, have stated that joint cracking does not cause arthritis.9 Habitual joint cracking does not correlate with arthritic changes but does correlate with loss of grip strength and soft-tissue swelling.22
Taking an engineering approach, cracking the knuckles repeatedly over many decades could in theory damage the cartilage covering the joint. Comparisons have even been made with the mechanical wear and tear accrued over time by ship's propellers, but the evidence that the same is happening in people's hands is thin.4,17
So how did the idea of a relationship between knuckle cracking and arthritis emerge? It is true that people who already have arthritis sometimes find their joints crack because the cartilage of the surface of the joints has been damaged. However, it is unusual for this to be the first symptom, and it is more likely to be a consequence of damage, rather than a cause.
Established risk factors for arthritis include age, a family history of the condition, previous accidents involving the hand(s), and a lifetime of working with the hands (such as a career in heavy labour).19
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 is induced as part of the treatment. The back, knees, elbows and all other movable joints are subject to the same kind manipulation as knuckles.23
On the next page we look at what causes cracking joints, whether you should be worried about the cracking and popping of a joint and how to take care of your joints.