What actually happens when my back ‘cracks’?

I recently had an eye-opening conversation with a friend of mine who lives over East. He explained that he had ‘put his back out’ at the gym, and was going to see a therapist to ‘put it back in’. 

I was immediately interested in the language he used and what his ‘back out’ looked like in his mind, and what the treatment of ‘putting it back in’ might entail (because in fact, I hear this quite a lot in physiotherapy practice).

He said, “you know, get it cracked, and put it back into alignment”. 

After a juicy discussion and a part scientific exploration, part social experiment I asked him to draw what he imagined his back looked like, and what he thought cracking (or spinal manipulation) did to his spine. I was shocked. He had drawn his spinal disc half-way off the page!! 

For players at home, fortunately, it is literally impossible for a spinal disc to leave the spine like this, but it got me thinking what peoples’ perceptions are of their backs, and what their perceptions are of common physiotherapy treatments such as spinal manipulation (aka back cracking). 

So, I put my investigator cap back on and looked into the research and found that over 70% of people think that the cracking sound of a spinal manipulation was due to vertebra returning to their normal position or vertebrae rubbing against each other [1]. The belief is remarkably common!! But unfortunately, this is incorrect according to the most up to date research. 

….…..”Then what is the TRUTH to ‘back cracking”, I hear you ask????

Joint manipulation doesn’t put anything back into place.

Spine joints and discs don’t go out of place (like in my friend’s drawing) in the first place, even with immense pain, or even when the pain creates crooked, bent over postures!!

“So, what actually happens when my back is cracked?”

The most up to date research in this area identifies that the noise made is from a rapid formation of a new gas bubble, formed from the fluid inside our joint when the joint is stretched apart [2]. This gas bubble can last for around 20 minutes before the gas reabsorbs into the fluid (hence why you can’t crack the same joint twice within 20 minutes or so). 

“If it’s only a gas bubble, then why does joint cracking often feel so relieving, just like something did pop back into place???” 

Great question, and a very long question to answer (don’t worry, I’ll keep it short). Put simply, the most up to date understanding is that cracking does some cooky and cool things to our nervous system, it chills out the pain signals going up to our brain, it chills out the pain processing centres in our brain, and in summary, it gives our body pain relief and muscle relaxation so we can keep moving normally to recover. 

This matters because it’s helpful to know:

  1. Our spines are robust and don’t just pop in and out of place, even if they can be excruciatingly sore at times.
  2. Spinal manipulation can be a helpful pain reliever, but not because it’s ‘realigning something’, but because its messing with our nervous system (in a good way!!). It gives us a chance to keep moving normally which is the ultimate recovery tool. 
  3. We as therapists need to be mindful of our language and not contribute to incorrect perceptions like my friend had of his spine being out of place. 

I could write on this topic for days, but I will leave it there. I should probably let my friend over East know ☺

Beliefs in the population about cracking sounds produced during spinal manipulation.
Demoulin et al 2018

Real-Time Visualization of Joint Cavitation Kawchuk et al 2015

Extra Resources about Back Pain. 

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