“How this common misconception got started is not clear, but I suspect the commonality of osteoarthritis in the hands as we age and the commonality of knuckle-cracking, along with the distinct noise thus created, were all factors,” Hylland says. “Given the annoying nature of the sound, I suspect parents were quick to use these observations to halt the behaviour and, eventually, repetition through time solidified its justification.”
Article source: https://www.huffingtonpost.co.uk/entry/does-cracking-knuckles-lead-to-arthritis_uk_636e580ce4b09d758bd6ae36