In what might be one of the most obscure scientific discoveries of 2015, researchers have identified once and for all what happens when you crack your knuckles.

It had been assumed for almost 50 years that joint cracking – which gives great relief to some yet makes others shiver with disgust – occurred when a change of pressure inside the joint caused gas bubbles to pop as the knuckle was bent or pulled.

Now a team of international researchers, including an Australian, who used magnetic resonance imaging (MRI) to watch this event in real time, have overturned that view.

They found that rather than gas bubbles collapsing, when a man's fingers were gently pulled to force a joint crack the images show a "cavity" or small pocket of gas forming and remaining inside the joint.