Cracking your knuckles: Ultrasound shows 'fireworks exploding in the joint'

Scientists have used ultrasound to see just what happens when you crack your knuckles, with results showing what looked like a "firework exploding in the joint". The team, presenting its findings at the annual meeting of the Radiological Society of North America (RSNA), said the ultrasound showed a bright flash when the knuckle cracked and this, they believe, is related to a gas bubble in the joint. Researcher Robert D Boutin said: "It's extremely common for joints to crack, pop and snap.