Knuckle Cracking 101: for Therapists and Clients

Bodyworkers are one of the many types of professionals who physically and repeatedly rely on hand strength and dexterity for optimal work performance. Knuckle cracking is an unconscious custom practiced by many who rely on their hands in an attempt to loosen or relax the phalanges.

Controversy has long surrounded the benefit and/or detriment of knuckle cracking. While some claim the end result of knuckle cracking is arthritic hands, others tout it as a completely normal and healthy act. Whether you do it yourself, administer treatments to or simply care for a chronic cracker, being familiar with the anatomy, physiology and possible pathology of this habit can help in sorting out the details of this on-going debate.

What occurs during knuckle cracking? Research on joint cracking is sparse. A joint capable of cracking is a diarthrodial joint, where two bones contact one another at their cartilage surfaces. These surfaces are surrounded by a joint capsule, which is filled with synovial fluid to lubricate the joint. Synovial fluid contains dissolved gases including oxygen, nitrogen and carbon dioxide.

According to Raymond Brodeur on the Ergonomics Research Laboratory at Michigan State University, “As the joint capsule stretches, its expansion is limited by a number of factors. When small forces are applied to the joint, one factor that limits the motion is the volume of the joint. That volume is set by the amount of synovial fluid contained in the joint. The synovial fluid cannot expand unless the pressure inside the capsule drops to a point at which the dissolved gases can escape the solution; when the gases come out of solution, they increase the volume and hence the mobility of the joint. The cracking or popping sound is thought to be caused by the gases rapidly coming out of solution, allowing the capsule to stretch a little further.”

This predominant theory alleges that a pulled finger stresses the joint capsule’s capability, triggering a change in the synovial fluid for increased volume. The synovial fluid’s air bubble forms and quickly bursts, making the characteristic ‘cracking’ sound.

Brodeur adds, “If you take an x-ray of the joint after cracking, you can see a gas bubble inside the joint. This gas increases the joint volume by 15 to 20 percent; it consists mostly (about 80 percent) of carbon dioxide. The joint cannot be cracked again until the gases have dissolved back into the synovial fluid, which explains why you cannot crack the same knuckle repeatedly.”

According to Jonathan Cluett, MD, an orthopedic surgery fellow in sports medicine and arthroscopy in California, a cracking joint can also be due to the tendons and ligaments crossing over a joint. Ligaments and tendons crossing over bones may produce a pop or cracking sound as they tighten and snap over a moving joint. This is the likely mechanism responsible for inadvertent crackling hands of a massage therapist, or in any other manually demanding occupation.

Does knuckle cracking actually loosen the finger joints? As Brodeur explained, knuckle cracking does temporarily widen the joint space between phalanges. However, it does not lengthen and relax the muscles of the hands and fingers. Peter Bonafede, MD, medical director of the Providence Arthritis Center, suggests replacing knuckle cracking with the more useful practice of bending and stretching out of the fingers. When hands get cramped or tired, finger bending and stretching serves to oxygenate and lengthen fatigued muscles.

WebMD suggests trying the following hand, wrist and finger exercises for increasing flexibility and strength:

Rotating your wrist up, down, and from side to side.
Stretching your fingers far apart, then relaxing them, then stretching them again.
Squeezing a rubber ball.
Wrist curls and extensions with a light weight.

Is there any danger to knuckle cracking? This question evokes the most controversy. Most knuckle crackers support their habit by citing a mid-1970s study of 28 people concluding that knuckle cracking does not cause or lead to arthritis. Many specialists in this area claim no harm is being done, as long as there is no pain, swelling or mobility restriction associated with the cracking.

A 1990 study published in the Annals of Rheumatic Diseases evaluated 300 participants. The authors came to a similar conclusion, where the prevalence of arthritis in habitual knuckle crackers was comparable to those not identified as habitual knuckle crackers. However, a significantly greater number of knuckle crackers suffered from decreased hand function and reduced grip strength.

The cracking of finger and hand joints can be deliberate or unintentional. In either case, maintaining flexibility in the hand is governed by the health of its muscles, tendons and ligaments. Stressing the joint capsule may result in an audibly satisfying pop, but the long- term results show potential for tissue damage. If you or someone you know is a habitual cracker, or experiences inadvertent snapping with hand activity, periodic finger bends, stretches and exercises are the best preventative measure for maintaining hand health.