Knuckle-cracking not linked to arthritis

For some, cracking their knuckles before beginning the day is a morning ritual; while for others, it is a way to pass time as they ponder a thought or read a book. But is the old-age myth that knuckle-cracking gives us arthritis true – or is it just a harmless habit?

Dr Donald Unger claimed to have known the answer for some time when he published a letter to the Editors of the Arthritis and Rheumatism journal in 1998.

Cracking of the knuckles is when a person deliberately produces clicking sounds by bending their fingers into unusual positions. These positions are usually ones their own muscles are unable to achieve. However, cracking a joint that has been exercised recently is generally recognised to be comforting.

Many studies have concluded there is no increased preponderance of arthritis of the hand due to knuckle cracking; however, habitual knuckle-crackers were more likely to have hand swelling and 25% lower grip strength. Habitual knuckle-cracking was associated with manual labour, biting of the nails, smoking, and drinking alcohol in the study participants and their families.

Dr Unger reports he had been cracking the knuckles on his left hand at least twice daily over a 50-year period, while the right knuckles was never cracked.

This unique study was undertaken in response to advice from various well-meaning relatives who warned him against cracking his knuckles in his early life, and if continued for half a century would cause considerable damage.

However, Dr Unger’s right hand remained arthritis-free throughout his life – as did his left hand.

Dr Unger was awarded the 2009 Ig Nobel prize for Medicine, presented annually on the eve of the ‘real’ Nobel Prizes by the organisation Improbable Research, for “achievements that first make people laugh, and then make them think”.

Nearly one in five Australians has arthritis; and by 2050 it is expected there will be seven million people with the painful condition.

Another earlier study by Swezey and Swezey was published in 1973 by a man and his 12-year-old son, who, after seeing Dr Unger’s letter, reported their 10-year follow-up produced similar results; also recording no signs of arthritis in their cracked knuckles.

So, what causes the cracking sound? Cracking of a joint is most likely due to a rapid change in joint volume causing the brief formation of a bubble of gases such as carbon dioxide (CO2).

These gases are normally dissolved in the joint fluid and escape the solution when the pressure of the joint suddenly lowers. The unstable gas bubble rapidly implodes and is believed to be the cause of the cracking sound.

In the past, researchers have said joint cracking could be confused with the “snapping” sound made by stiff tendons or other bands of soft tissue sliding between muscles or over bony outcrops.

They claim it is also different from the grinding sound (called “crepitus” by health professionals) that results from movement of a joint with roughened or worn cartilage.

Do you crack your knuckles? Share your thoughts on this topic in the comment box below.