There is quite a bit of speculation and vague explanations around joint cracking. As young people we are often told not to crack our knuckles because “it’ll give you arthritis” or that the cracking sound is due to “bubbles popping” within the joint. But what’s really going on when our joints make sounds like that?
The history of our knowledge about “the crack” is a winding road. One of the first scientific attempts to come up with an explanation for the phenomenon was made by a pair of British researchers in 1947, who took a series of X-rays to see exactly what was happening inside the joints. Their conclusion was that it was caused by bubbles popping out of the synovial fluid like the world's smallest thunderclap. This answer was widely accepted for roughly a quarter of a century.
In 1971 that hypothesis was cast in doubt, and a new explanation pinned the blame on the collapse of those gas bubbles rather than their formation. This is the story that most of us have heard throughout our lives.
Then several years ago, yet another investigation based on magnetic resonance imaging (MRI) found that the bubble-formation hypothesis was the correct one all along.
Real-time magnetic resonance imaging shows that the exact opposite of what many believe to be true: the cracking sound indicates the formation of a bubble of space in the joint, not a bubble collapsing. These observations are consistent with a known process where opposing surfaces resist separation until a critical point after which they separate rapidly, creating gas cavities. This study was supported by another study in 2015 that used ultrasound to determine the sequence of bubble and sound.
Image of the hand in the resting phase before cracking (left). The same hand following cracking. Note the dark space inside the joint (yellow arrow).
Creating space in the joints can lead to increased comfort and mobility. During a chiropractic adjustment, more space is being created between the vertebrae, taking pressure off the nerves and allowing more movement.
It’s important to keep in mind that a cracking sound is not the same thing as a chiropractic adjustment. A chiropractic adjustment is targeted to address specific alignment issues. Not every adjustment will be accompanied by a noise, and not every noise means you’ve gotten an adjustment. After an examination, a chiropractor will be able to tell where and how your unique body should be adjusted to best help you. Chiropractors spend years studying the musculoskeletal system and the nervous system,to understand effects of these disorders holistically.