Despite science, there’s still a lot we don’t know for certain about the human body. Among the mysteries that surround yawns and dominant hands, knuckle cracking is one behaviour that has remained unresolved since the 1900s, when scientists began to research the popping sound it produced. A common parental belief warns that knuckle cracking causes hand arthritis, but does it, really?
Snap, crack and pop away
I was 10 years old when I cracked my knuckles for the first time. Some of my friends were already popping them – hooked on the sound – but I was always afraid of pulling my fingers off to do that, too. Until a cold geography lesson in primary school. That day, as we learnt about the water cycle, I grasped my left index finger with my right hand and simply yanked, until I heard the distinctive crack. As a curious child, I was immediately fascinated by my finger’s ability to stretch so far without it causing pain and soon, I began cracking my knuckles, over and over again.
My fascination quickly wore off, but still, I found myself snapping my knuckles whenever I could or felt like I needed to. Knuckle cracking became a way to release tension and, like other fellow knuckle crackers, a way to combat restlessness, keep my hands constantly busy and relieve stiffness in the joints. By now, more than a decade later, knuckle cracking is an essential part of my lifestyle, one that feels as urgent as sneezing or scratching an itch.
What’s exactly at work
The knuckles, known as the metacarpophalangeal joints, are some of the body’s smallest joints, located where the metacarpal (hand) bones meet the phalanges (finger bones) of the hand. They are also one of the easiest joints to pop. Though the origin of this popping sound is still undetermined, since 1971, research has widely attributed it to the collapse of bubbles when fingers are forcibly stretched or bent during knuckle cracking, a phenomenon which only takes 300 milliseconds to process.
Pulling the joints apart, knuckle cracking increases the space between the joints, which in turns stretches the synovial fluid that covers and lubricates them. Pressure inside the fluid is then reduced. When this pressure reaches a minimum level, nitrogen, carbon dioxide and oxygen already dissolved in the synovial fluid cause small gas bubbles to form, in a process called tribonucleation.
The bubbles burst instantly and their collapse produces the audible knuckle crack. However, they only do this partially – as three mathematical equations revealed in 2018. While it may appear as an incomplete process, the partial collapse is significant enough to leave a bubble trace behind that can be picked up by MRIs and cause a crack that can reach 83 decibels. The gas bubbles are fully reabsorbed back into the synovial fluid 20 minutes after the crack and pressure is restored back to its normal state, a period in which the same knuckle can’t be cracked twice in a row.
Knuckle cracking: an early sign of arthritis?
Although research is limited, studies agree: knuckle cracking doesn’t lead to degenerative joint conditions like arthritis.
In fact, a retired allergist named Donald Unger went so far as to conduct an experiment on himself just to find out whether knuckle cracking caused arthritis. For 50 years, he cracked the knuckles on his left hand twice a day while leaving the knuckles on his right hand mostly unscathed. At the end of the study, no arthritis, nor any other form of joint damage developed in either hand, despite having cracked his left knuckles more than 36,500 times. A study in 2017, that came to the same conclusion, suggested that knuckle cracking could even increase range of motion in the joints.
Some studies point to knuckle cracking possibly causing other forms of functional hand impairments, such as weakened joints. One study carried out in 1990, found out that knuckle crackers had an average lower grip strength than those who didn’t pop their knuckles. The development of arthritis, however, was the same in both groups. Another study with habitual knuckle crackers (who crack their knuckles more than five times a day) and non-knuckle crackers, discovered that knuckle cracking was associated with increased thickening of the metacarpal cartilage that surrounds the hand’s bones. In this case, grip strength was the same in both groups. Despite these findings, further investigations to support these results have not been presented.
Yet for more than 10 million people in the UK who suffer from conditions affecting the bones or joints, such as rheumatoid arthritis, knuckle cracking is highly discouraged. The amount of force applied and the individual knuckle cracking technique have led, in very rare occasions, to ligament sprains after particularly strong popping. The knuckles are stable joints, but it is also possible to dislocate them (the index and little fingers, especially) when sufficient external force is applied.
Healthy joints, healthy body
As a rule, knuckle cracking is unlikely to lead to arthritis. Despite what myths suggest, the habit is mostly harmless in the absence of pain, swelling or changes in the shape of the joint. Seek medical attention if knuckle cracking occurs with any of these symptoms, however, as the discomfort may indicate joint trauma, a worn cartilage or pre-existing underlying conditions like gout, which could be aggravated by the stretch and pull of knuckle cracking.
For those who wish to, there are good reasons and ways to leave knuckle cracking behind, even if the habit isn’t necessarily harmful. Meditation, stretches and breathing exercises can help to ease the undercurrent of nervousness that leads to knuckle cracking. If distraction is needed, using stress-relief balls and fidget gadgets can keep the hands occupied, which will lessen the urge. Breaking years of compulsive knuckle cracking requires a special level of dedication, but for those who have made it a lifelong quirk, know that (for the most part) it will be fine.
For medical guidance on how to preserve healthy, strong and mobile joints, visit one of Top Doctor’s expert orthopaedic surgeons today.
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