Cracked it! Scientists solve puzzle of why knuckles pop when pulled

An MRI scanner, a bespoke finger-pulling device and a willing knuckle-cracker helped researchers put their finger on the answer

For centuries, scientists have wrestled with the deepest mysteries of space, time and the nature of consciousness. But not all of them. Some turn their minds to what can fairly be described as lower-hanging fruit. Like why our knuckles crack when we pull them.

The question has never been the subject of sustained scientific inquiry, but the puzzle crops up in medical literature reaching back more then 50 years. It began, perhaps, with a German physician called Nordheim, who in 1938 demonstrated that most joints in healthy people can be made to pop when pulled upon.