Knuckle cracking lowdown

Some mysteries remain impermeable to the light of human inquiry; what is the Loch Ness Monster, who was Jack the Ripper, what happens in the Bermuda Triangle, and what are the Twilight series scriptwriters doing? Right up there with these deep unknowns is what happens when you crack your knuckles but according to a new study we might have at least “cracked” the knuckle mystery.

Knuckle cracking has been around as long as children have gathered in groups and one human wanted to intimidate another (rumour has it that Julius Caesar was a notorious knuckle cracker*). Back in the 1940s researchers from the UK came up with the first explanation for knuckle cracking saying that they believed it resulted due to vapour bubble formation. That explanation was brought into doubt though when other researchers suggested collapsing bubbles as the cause.

The new research though has solved the riddle by being able to record via MRI what is happening in a knuckle in real time as it is cracked.

The researchers achieved this by firstly enlisting for their experiment a chiropractor who is able to crack each of his finger’s without fail provided there had been some recovery time in between. The chiropractor inserted each finger, one at a time, into a tube connected to a cable that was slowly pulled until the knuckle joint cracked. The actual crack occurred in less than 310 milliseconds but using MRI video the researchers were able to record the event.

The MRI video revealed that the cracking was associated with the rapid creation of a gas-filled cavity in the synovial fluid of the joint. What was happening was that as the joint surfaces separated there was no more fluid available to fill the joint volume and, a bit like forming a vacuum, a cavity is created and that is the popping sound that we call “cracking”.

This doesn’t really answer the question of whether joint-cracking is good or bad. While the amount of force involved in cracking your knuckles generates enough energy to damage hard surfaces, habitual knuckle cracking has not been proven to harm long term joint health.

If you find yourself a little dispirited at having one of life’s mysteries dispelled then don’t despair because the researchers found something else. The MRI videos revealed something never seen before; just before a knuckle cracked a white flash appeared in the joint. The researchers say this white flash may just be water suddenly being drawn together before the joint cracks. However, might that flash not be a knuckle-reflection of the same energy that was released in the original “big bang”**! Or could it be a knuckle-fairy letting loose with an expletive***? It seems that as so often happens, in dispelling one mystery we have found another.

*Deliberate historical fabrication

**Wild speculation

***Incredibly likely