So, I never understood the "pull my finger jokes" but this is a really cool piece of research!
Fryer’s fingers were inserted one at a time into a tube connected to a cable that was slowly pulled until the knuckle joint cracked. MRI video captured each crack in real time—occurring in less than 310 milliseconds.
In every instance, the cracking and joint separation was associated with the rapid creation of a gas-filled cavity within the synovial fluid, a super-slippery substance that lubricates the joints.
I hope they settle the debate about whether or not cracking your knuckles is good for you or not (sorry Mom, I just don't think it hurts anything!) I'm looking forward to their next paper.
"Scientists have calculated that the amount of force at work when you crack your knuckles has enough energy to cause damage to hard surfaces, yet research also shows that habitual knuckle cracking does not appear to cause long-term harm. Those conflicting results are something Kawchuk and his team plan to investigate next."