Probing Question: Does cracking knuckles cause permanent damage?

cracking knuckles
James Collins

You've done it more often than you're willing to admit. Against the steering wheel of your car. On the arm of your office chair, or right on the desk. You do it mostly when you're alone, but sometimes you do it in public—under the table in a restaurant.

Most of the time you get away with it, but sometimes you get caught, and people turn away in disgust. You suspect that it's unhealthy, but it feels so good that you just don't want to stop. And yet maybe it's harmless—you're not really sure. Does cracking your knuckles cause permanent damage?

According to Sanjiv Naidu, Penn State professor of orthopaedics, it does not.

"Plain old knuckle-cracking should not cause any damage. It does not strain the ligaments or the tissues, or overextend them enough to cause arthritis," Naidu says. "It also should not cause joint weakness, on a long-term basis. Anatomically, physiologically, and mechanically, there's no reason it should cause harm."

Elaborates Naidu, "You 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," The forces generated by knuckle-cracking are relatively small in comparison.

So your mother's childhood warnings were just old wives' tales. But what makes that disconcerting sound? Naidu explains that the cracking noise is caused by a gas, mainly carbon dioxide, that is usually dissolved in the synovial fluid that encapsulates most joints. "If you pull on the joint or distend the joint capsule," he notes "the walls of the capsule expand and lower the pressure on the fluid inside it. The gas then comes out of solution suddenly and forms bubbles, which makes a popping noise."

The stretching of the capsule also allows a temporary increase in the joint's range of motion. "When you move the joint back into position," Naidu notes, "the fluid comes under normal pressure again, and the bubbles gradually go back into solution." The time it takes to re-dissolve the carbon dioxide into the synovial fluid prevents the knuckle from cracking again for a few minutes.

Although the actual process of cracking a knuckle may take only a few milliseconds, the relief that some people feel from it is palpable. Chiropractors make a business out of manipulating joints to reduce stress, and dedicated joint-crackers even have their own Web site and discussion board, on which to exchange anecdotes. If you're among them, it's likely that the only consequences you'll face for your popping and snapping will be comments from friends and funny looks from innocent bystanders.

Sanjiv Naidu, M.D., Ph.D., is professor of orthopaedics and rehabilitation at the Penn State College of Medicine and an orthopaedic surgeon at Hershey Medical Center, specializing in hand surgery and joint replacement. He is medical director of the Hand and Upper Extremity Institute of Central Pennsylvania and also holds an appointment with the Materials Research Institute at University Park, where he studies the properties of polymers used in implant surgery. He can be reached at snaidu@psu.edu.

Last Updated April 10, 2006