This is a guest post by Dr. Kent W. Davidson, M.D who works with our Doctors Online partners at eDocAmerica.

Urban legend would indicate that knuckle cracking leads to arthritis of the joints of the hand. It would be a gross overstatement, however, to say that the medical literature has thoroughly explored this connection. This is one of those quasi-medical issues that is scarcely mentioned in medical school curricula.

What causes the knuckles to pop?

People primarily tend to crack two groups of hand joints. These are the joints between the bones of the fingers (interphalangeal joints) and the joints formed where the bones of the hand meet the fingers (metacarpophalangeal joints). By manipulating these joints, either through extreme flexion, extension, or sideways bending, pressure in the joint space decreases, and a gas bubble forms in the joint fluid. This results in rapid movement of joint fluid toward the bubble causing it to burst which leads to the characteristic cracking sound.

Why do people crack their knuckles?

For some people, knuckle cracking is a habit or something that they do out of boredom. Others say that it helps relieve joint discomfort and improves the range of motion of the hand joints.

What type of arthritis is thought to be associated with knuckle cracking?

Knuckle crackers allegedly are at risk of developing osteoarthritis, a degenerative disease affecting the joint cartilage. The additional "wear and tear" of the joints due to knuckle cracking is thought to be the culprit in the development of arthritis. Osteoarthritis is a potentially debilitating disease that affects a majority of individuals over the age of 65. If a definite link between something as simple as knuckle cracking and the development of osteoarthritis was confirmed, modifying one's behavior could reduce the risk of developing the disease.

What is the existing evidence?

The first study exploring the connection was published in 1975. Twenty-eight nursing home residents were polled and asked if they cracked their knuckles currently, or if they had in the past. These responses were compared to x-rays taken of the hand joints. Interestingly, the number of subjects who had evidence of osteoarthritis was lower among the knuckle crackers than in a comparison group who indicated that they had not cracked their knuckles. While the authors did not go as far as saying that knuckle cracking provided a protective effect, they dismissed the notion that knuckle cracking leads to the development of osteoarthritis.

A second study evaluated 300 subjects over the age of 45 for the presence of habitual knuckle cracking and hand arthritis or dysfunction. An increased prevalence of osteoarthritis was not found in the group that habitually cracked their knuckles. This group, however, was more likely to have hand swelling and lower grip strength. The authors concluded that habitual knuckle cracking could cause functional hand impairment but not in the development of osteoarthritis.

The most recently published study took a more scientific approach than the previously performed studies. Hand x-rays were used to confirm the presence of osteoarthritis in the 135 subjects included in the study. A control group of 80 subjects was also identified who did not have osteoarthritis. Questionnaires were given to both groups to gather information about knuckle cracking, as well to learn about their risk factors for the development of osteoarthritis. This study even calculated "crack-years," to quantify the length of time that subjects cracked their knuckles in order to explore the possibility of a "dose response" relationship between knuckle cracking and the development of osteoarthritis. The study found that those who had osteoarthritis were no more likely to have cracked their knuckles than the subjects in the control group who did not have osteoarthritis.

Although it may not make the practice any less annoying, the evidence available today indicates that cracking your knuckles will not cause you to develop arthritis.

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