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Knuckle Cracking and Arthritis

Ashley Nelson

February 20, 2009

Introduction

knuckle cracking.jpgWe have all done and heard it before. Our parents more than likely told us to stop doing it because of its irritating sounds. If that was not enough to convince us to stop cracking our knuckles, our parents added that our socially bothersome behavior can be physically troublesome and can consequently lead to arthritis. So, does habitual knuckle cracking eventually lead to arthritis or cause damage to the joints? Or, is this habit just another fabricated old-wives’ tale with no concrete evidence?

 

How joints work

osteo-joint.gifhealthy-joint.gifJoints are locations where two or more bones make contact and allow one to move, pivot, bend, and breathe. The term ‘articular’ is used in reference to a joint, whereas, the term ‘periarticular’ means around the joint. There are hundreds of joints in the body, including knuckles. Some of them, like the ones between the vertebrae of the back, are quite strong and allow only slight movement. In contrast, other joints such as the ones in the wrists, arms, and legs, are very flexible (Moyer, 1997). Ligaments are strong fibrous bands that hold the bones together. Muscles, on the other hand, stretch and shrink in order to provide movement for the joint. Cartilage, a spongy material, covers the bone and prevents the bones from rubbing against each other, providing the joint to move smoothly. According to WedMd (http://www.webmd.com/osteoarthritis/guide/arthritis-basics), “the joint is lined by a tissue called synovium which contains synovial fluid that nourishes the joint and helps reduce friction.”

 

 

 

 

 

As far as if arthritis can develop in any joint, evidence shows that it does not strike every joint. Moreover, “different forms of arthritis tend to prefer different joints” (Moyer, 1997). A look into what exactly arthritis is and what causes it is imperative in understanding how different types of arthritis affect the joints.

What is arthritis and what causes it

Arthrite_rhumatoide.jpgArthritis is a group of conditions involving damage to the joints. It is not a single disease, but includes over 100 rheumatic diseases that cause pain and inflammation in the joints. Some of the most prevalent types of arthritis are osteoarthritis, rheumatoid arthritis, and gout. “Osteoarthritis involves the breakdown of cartilage and often associated with old age and joint injuries, and commonly occurs in hips, knees, feet, and spine. Rheumatoid arthritis is more serious than osteoarthritis. It involves joint inflammation, weight loss, loss of appetite, fatigue, and sometimes inflammation in parts of the body besides joints. Gout is inflammation and swelling in one or a few joints, typically toes. It is often a result of too much of certain food and wine” (Moyer, 1997).

Arthritis is a very common disease, especially among Americans. According to the Arthritis Foundation (Moyer, 1997), around 4o million Americans have some form of arthritis. More astonishingly, almost half of Americans over sixty-five years of age has some form of arthritis. Younger people have a relatively lower risk of developing arthritis. “There are around 250,000 documented children who suffer from arthritis” (Moyer, 1997).

Since there are various types of arthritis, a particular, universal cause for the disease has not been found. In fact, there is a good chance that there are many causes. One thing for sure is that inflammation is the body’s way of responding to a disease or injury which naturally causes swelling and can eventually lead to tissue damage. According to the John Hopkins Arthritis Center (http://www.hopkins-arthritis.org/arthritis-news/2007/knuckle-cracking-and-arthritis.html), “an unknown exposure to environmental stimuli” is considered a possible cause for inflammatory arthritis. “Aging and excessive mechanical stress” predispose older people in developing osteoarthritis. Researchers, though, are currently studying the relationship between heredity, everyday behaviors, and arthritis.

Despite the fact that the exact causes are not currently known, various risk factors exist for the arthritis. A risk factor is a behavior or trait that raises a person's probability of developing a disease or harm to his or her health.

 Some risk factors for arthritis as identified on WebMD (http://www.webmd.com/osteoarthritis/guide/arthritis-basics) include:

What happens when you crack your knuckles

finger hand.gifAs previously stated, joints contain a capsule of synovial fluid that protects the joint and prevents friction on it. The synovial fluid contains oxygen, nitrogen, and carbon dioxide. Once the joint is popped or cracked, gas is quickly released. “The stretching of the capsule lowers the pressure inside the joint and creates a vacuum which is filled by the gas previously dissolved in the synovial fluid” (http://www.hopkins-arthritis.org/arthritis-news/2007/knuckle-cracking-and-arthritis.html). A bubble is then formed which bursts creating the cracking or popping sound. Knuckles cannot be re-cracked or re-popped immediately easily because it takes time for the gases to return to the synovial fluid.

Joints may make cracking sounds when there is a loss of smooth cartilage and a rough joint surface. This typically occurs within arthritic joints. In addition, popping sounds occur when a tendon’s position moves slightly out of place and returns to its original position. The knee and ankle can make a cracking sound when the ligaments tighten as one moves his joints” (http://www.hopkins-arthritis.org/arthritis-news/2007/knuckle-cracking-and-arthritis.html).

Popular claims

Claims from different sources have been made about the knuckle-cracking and arthritis myth. Many of them come to a general consensus on the effect of knuckle cracking has on arthritis. However, since they are only popular claims, there is no direct scientific evidence to support the claims. The claims, nevertheless, are each presented by qualified physicians.

Claim 1

In a question and answer interview, rheumatology fellow at John Hopkins University Arthritis Center, Dimitrios Pappas, M.D. was asked if cracking knuckles or joints can lead to arthritis. Pappas responded by saying that “there is no evidence of such an association. In limited studies performed there was no change in occurrence of arthritis between habitual knuckle crackers and non-crackers.” When asked if one can make their current arthritis worse by cracking his or her knuckles, Pappas responded by saying, “No. However theoretically “knuckle – cracking” in patients with weak or damaged joints due to arthritis could potentially lead more easily to ligament injury or acute trauma to the joints” ” (http://www.hopkins-arthritis.org/arthritis-news/2007/knuckle-cracking-and-arthritis.html).

This article was published on the web as an information source by the John Hopkins Arthritis Center. Each month certified physicians post articles pertaining to arthritis news. Since this organization focuses on the overall well-being of people, one can assume that this information was posted in an impartial way. By referencing to past studies, the article dismisses the claim that knuckle cracking leads to arthritis. The information here is presented as a widely available source for the public so they can be more informed about their health, and in particular, the effects of knuckle cracking.

Claim 2

According to Sanjiv Naidu, Penn State professor of orthopedics, cracking one’s knuckles cannot cause permanent damage. He bases his assertion on the fact that “it does not strain the ligaments or the tissues, or overextend them enough to cause arthritis. It also should not cause joint weakness, on a long-term basis. Anatomically, physiologically, and mechanically, there's no reason it should cause harm." Naidu goes on to state that one would “literally have to disrupt the joint capsule through excessive force—like a ligament injury in a knee, or 'skier's thumb,' for example—to cause chronic, long-term damage" (http://www.rps.psu.edu/probing/knuckles.html).

This article was published by Stacey Tibbets on the “Research Penn State” website.  The page claims to be an “online magazine of scholarship and creativity.” One would therefore assume that the claim presented by the author should be valid because of its history as an authoritative source. Similar to the John Hopkins Arthritis Center website, this webpage would have no reason to be bias towards the knuckle cracking claim in either direction. Their apparent motivation for the article was to answer a submitted question from the websites’ “probing questions” section. Dr. Sanjiv Naidu is frequently quoted throughout the article. He appears to be a reliable, qualified source for he is a professor of orthopedics and rehabilitation at Penn State College of medicine and an orthopedic surgeon at Hershey Medical Center. Even though his range of professional titles shows that he is very qualified, he never refers to past research studies for evidence during his interview but supplies an answer in anatomical, practical terms.

Claim 3

Unlike the other two aforementioned claims, a short article posted in the New York Times used direct support from a study published by The Annals of the Rheumatic Diseases and study in The Western Journal of Medicine to come to his conclusion that “knuckle cracking will not cause arthritis, though it may lead to other problems” (O’Connor, 2005).

This article was published by Anahad O’Connor in the Health section of the New York Times. The articles’ apparent reason for being published was to serve as a way to inform the public and to disprove an old wives’ tale. Although the article is short in length, it does refer to various studies to back up its position in not supporting the claim that knuckle cracking leads to arthritis. The documentary evidence used in the article includes information from The Annals of the Rheumatic Diseases and The Western Journal of Medicine. Since both sources came up with similar results, O’Connor was able to have sufficient support in formulating his own plausible explanation.

Research studies

In a 1990 study published in The Annals of Rheumatic Diseases, Jorge Castellanos and David Axelrod looked to see if habitual knuckle cracking eventually led to a decrease in hand function. Their study consisted of three hundred consecutive patients at the medical clinic of Mount Carmel Mercy Hospital, who were at least forty-five years old, and had no evidence of neuromuscular or malignant diseases, and had a clear memory of whether or not they would classify themselves as knuckle crackers of the past. Information pertaining to “age, sex, occupation, income level, drug treatments, grip strength, smoking history, alcohol intake,  knuckle cracking and its duration, history of gout, hand trauma or surgery, hand swelling, carpal tunnel syndrome, presence of Heberden’s/Bouchard’s nodes, hand contractures, generalized osteoarthritis, neuropathy, and family history of these problems” (Castellanos et al., 1990) was recorded.

 

Of the 300 subjects, seventy-four admitted to habitual cracking for eighteen to sixty years (Castellanos et al., 1990). The other 226 patients denied having had the habit. “The age and sex distribution of both groups was similar, as was the prevalence of gout, generalized osteoarthritis, carpal tunnel syndrome, trauma or surgery to the hand, Heberden’s or Bouchard’s nodes, and hand contractures” (Castellanos et al., 1990).The biggest noted difference between the groups occurred within hand swelling. Eighty-four percent (Castellanos et al., 1990) of habitual knuckle crackers had hand swelling, yet only six percent of non knuckle crackers had hand swelling. Results (Castellanos et al., 1990) also included that knuckle crackers were more likely to be manual laborers who more frequently drank alcohol, smoked, and bit their nails.

 

 

http://ard.bmj.com/cgi/content/abstract/49/5/308

Although this study does not suggest a relationship between knuckle cracking and hand arthritis, it does reveal that it may relate to a decline in hand function. Thus, habitual knuckle cracking is not supported.

In the follow-up letter for this study written by Simikin PA suggested that “people with unusually loose joints may be more prone both to crack their knuckles and to have joint damage because of the loose joints” (http://www.panix.com/~iayork/knuckles.html).

 

This study had a respectable number of subjects. One interesting fact I noticed in this article was the fact that knuckle crackers tended to be manual laborers and tended to have more hand problems than non knuckle crackers.  However, being a manual laborer, regardless of knuckle cracking tendencies, could lead to hand problems alone. This is a confounding factor that article does not include to mention. The article does however point out various interesting relationships among knuckle crackers. The follow-up letter adds that people with extremely loose joints are more inclined to crack their knuckles due to their loose joint.

 

Sweezy conducted a study in 1975 to test if the development of arthritis in the hand had anything to do with habitual knuckle cracking. It was designed to identify any bony enlargement and degenerative arthritis in metacarpal-phalangeal joints. Twenty-eight nursing home patients who had recollection of past knuckle cracking behaviors were used in this study. “The average age was 78.5 years, of whom twenty-three were women and five were men” (Sweezy et al., 1975). They were examined clinically and by x-ray.  In addition, twenty-eight school children at a summer camp were surveyed in order to determine the prevalence of knuckle cracking in a young population. The average age for this group was eleven years old, where eight were girls and twenty were boys (Sweezy et al., 1975).

The results of this study revealed that “only one patient with a history of knuckle cracking showed metacarpal-phalangeal (MCP) degenerative joint disease (DJD)” (Sweezy et al., 1975). More results are shown in the tables below.

 

 

 

 

 

 

 

 

 

 

 

http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1129752&blobtype=pdf

The above data reveals that there is a negative correlation between knuckle cracking and degenerative joint disease. The data also indicates that one of eleven positive knuckle cracking women had metacarpal-phalangeal degenerative joint disease, and five of twelve negative knuckle cracking women had metacarpal-phalangeal degenerative joint disease. Therefore, there is no positive correlation of knuckle cracking in the women with metacarpal-phalangeal degenerative joint disease (Sweezy et al., 1975). Juxtaposing the knuckle cracking in the old group to the young group showed that there is not a big difference in the prevalence amongst the two groups despite youngsters’ susceptibility to typical mannerisms.

The main flaw of this study was the small number of subjects involved, and thus, not much information can be completely derived from it. In addition, possible flaws in the data can arise when researchers depend on their subjects to self-report data. In this study, researchers asked the subjects to self-report their past medical history. Subjects could have easily had a mental lapse and submitted answers incorrectly, or they could have made themselves look like the “ideal” subject and could have given answers the researcher would want to see. On the other hand, researchers did a good job in comparing an older group with a younger group. This side-by-side comparison allowed the researchers to see any potential difference in arthritis prevalence among the age groups and what behaviors and qualities those people possessed. In conclusion, the data does not support knuckle cracking leading to metacarpal phalangeal degenerative changes in old age.

The verdict

Based on the popular claims and research studies previously mentioned, there is no scientific evidence suggesting that knuckle cracking is either detrimental or beneficial to one’s joints and health. However, according to the John Hopkins Arthritis Center and the Simikin PA article, repetitive knuckle cracking can do some possible damage to the soft tissue of the joint. Furthermore, it may lead to swelling of the hand and a weak grip. Clearly, if one is feeling pain when his or her joints pop, then “there could be underlying abnormalities of the structures of the joint, such as loose cartilage or injured ligaments,” (http://www.webmd.com/osteoarthritis/guide/arthritis-basics) and he or she should seek professional assistance. The best ways to prevent arthritis include eating a healthy diet in order to strengthen your bones and muscles, exercising in order to keep your muscles strong which can protect your joints, and staying at a healthy weight in order to avoid putting much strain on your joints. The bottom line is that there is no concrete evidence that cracking your knuckles will lead you down a road to arthritis, but a constant habit of knuckle cracking might provoke evil looks from the people around you. So, the next time you have an urge to pop your knuckles think twice about how it may affect your future health and the people in the same vicinity as you.


 

References

Castellanos, J, & Axelrod, D (1990). Effect of habitual knuckle cracking on hand function.

Annals of the Rheumatic Diseases, 49, Retrieved January 18, 2009, from

http://ard.bmj.com/cgi/content/abstract/49/5/308.

Moyer, E (1997). Arthritis : Questions You Have ... Answers You Need . Allentown, PA: People's

Medical Society.

O'Connor, A (2005, January 18). The Claim: Frequent Knuckle Cracking Can Lead to Arthritis.            The New York Times.

Pappas, D Knuckle Cracking Q & A. Retrieved January 14, 2009, from The John Hopkins

Arthritis Center Web site: http://www.hopkins-arthritis.org/arthritis-news/2007/knuckle-cracking-and-arthritis.html

Sweezy R.L & Sweezy S.E (1975). The consequences of habitual knuckle cracking. Western

Journal of Medicine, 122, Retrieved February 1, 2009, from http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1129752

Smith, M (2007, March 01). Arthritis Basics. Retrieved February 1, 2009, from Arthritis Web        site: http://www.webmd.com/osteoarthritis/guide/arthritis-basics

Tibbetts, S (2006, April 10). Does cracking your knuckles cause permanent damage?. Retrieved             January 14, 2009, from Research Penn State Web site:             http://www.rps.psu.edu/probing/knuckles.html

York, I (2008, March). Knuckle cracking: key to a better life, or the road to a living hell?. 

Retrieved January 13, 2009, from Ian York's Homepage Web site:             http://www.panix.com/~iayork/knuckles.html

 

 

 

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