Scientists have used an ultrasound machine to find out exactly what happens to our joints when they are cracked, thus putting an end to an old debate.
University of Alberta researchers published a paper based on MRI imaging of the finger joints, asserting that the cracking sound is caused by bursting air bubbles trapped in the so-called synovial fluid which surrounds our joints.
However, an ultrasound machine can record what happens inside our body by up to 100 times faster than a magnetic resonance apparatus, so another team of scientists decided to investigate the claim made by the University of Alberta researchers.
Led by Robert D. Boutin, radiologist at the University of California, the team recruited 40 healthy participants, of which 30 had the habit of cracking their joints regularly, while the remaining 10 never did so.
Participants were asked to crack the joints of each of their fingers while being monitored by an ultrasound device.
“What I saw was a bright spark like fireworks,” said Boutin. “It was an unexpected finding.”
Researchers suspect that the spark is caused by changes in pressure that occur in the synovial fluid.
What the researchers can say is that no immediate pain, swelling or damage to the cracked joints have been detected, and they found no difference between joints that are cracked regularly and those that are not.