What Really Happens When You Crack Your Knuckles
By: Alex Ha
Tags: Science, Arthritis, Health, Medicine, Habits

An Evidence-Based Review

Photo by Daiga Ellaby on Unsplash

“Cracking” your knuckles is the act of manipulating your joints, most commonly your fingers, in a way to produce a satisfying pop.

Like most people, it is something I often mindlessly do to cope with stress or boredom. I was constantly reminded by my parents to kick the habit as a kid because of the risk of developing bony deformities. Who was I to argue against their claims at such a young age?

But with the power of Google and an expensive graduate degree, I can finally educate my parents. Jokes aside, more research has been done surrounding the adverse effects of cracking your knuckles that have provided me with the evidence to support my claims.

What causes the pop?

The physiology behind the acoustics of cracking your knuckles have been unknown for a long time. A 2018 study created a mathematical model of events that is consistent with the widely accepted belief that the sound comes from bursting gas bubbles within the lubricating fluids of the joint.

It has been compared to blowing up a balloon and stretching it until it pops.

This process is very different from crepitus, it’s harmful counterpart. Crepitus is the act of rubbing two bones together which will inevitably cause discomfort and lead to some of the misconceptions associated with cracking your knuckles.

It is very unlikely to incidentally cause crepitus when trying to crack your knuckles because of the presence of the lubricating fluids in between the joint space known as synovial fluid.

What is the claim?

People often associate knuckle-cracking with an increased risk of developing arthritis, finger swelling, weakened grip, and decreased range of motion, at least my parents did.

Quick note: For the remainder of the article, I will be using arthritis and osteoarthritis interchangeably. Rheumatoid arthritis is an autoimmune condition, which means it’s caused by a dysfunctional immune system, not through a mechanical process.

To combat my parents nagging, I would often cite one specific case study that I heard about through a Youtube infographic show. It was a 1998 study about a physician who cracked only the knuckles of his left hand for 50 years and later compared both hands for any bony deformities.

The result was unremarkable! There were no signs of arthritis or any visible differences noted.

I was wrong to have only an anecdotal story of one physician’s experience in my arsenal to disprove my parents. Luckily for me, there has been more research done on this topic since then.

The Research

A retrospective case-control study gathered 135 patients (cases) with diagnosed arthritis and 80 patients without arthritis (controls) and documented their knuckle-cracking habits. This included their knuckle-cracking frequency, duration, and risk factors for hand arthritis.

Conclusion: Habitual knuckle-cracking does not seem to be a risk factor for developing arthritis.

Another prospective blind study focusing on 40 patients, of which 30 had a history of habitual knuckle-cracking, found promising results. The patients were evaluated by two orthopedic surgeons, who had no knowledge of which patients were knuckle crackers, and assessed their differences in hand swelling, grip strength, and range of motion; before and after knuckle cracking.

The researchers decided their research method wasn’t good enough and had two additional musculoskeletal radiologist (who were also unaware of who were the knuckle crackers) interpret ultrasound imaging of their hands.

Conclusion: There was no evidence of immediate adverse outcomes after knuckle cracking.

Drawbacks

There are still downsides to this seemingly harmless habit.

A 1999 research paper reported two cases of acute injury after attempting to crack their knuckles. One incident involved a partial tear of the ulnar collateral ligament (simply a thumb ligament), while the other case involved a subluxation (partial dislocation) of the extensor tendon on the pinky.

Both injuries were mild in nature and resolved after conservative management within 4 weeks.

The simple way to avoid any injuries associated with cracking your knuckles is to stop the motion if it gets painful. As we have all likely experienced, cracking your knuckles should be a painless and satisfying process (at least for some of us).

Personal recommendation

If you want to crack your knuckles, then do it! It will likely not result in any harm as the most up-to-date research has shown us.

Just be mindful of the extent of your finger flexibility.