cavitation in pumps will cause pitting in steel;i guess in knuckles it damage would be a cross between rate of cavitatin and the hardness of cartilage
LINK TO COLUMN: What’s actually cracking when you crack your knuckles? - The Straight Dope
As a small add, this only happens if the cavitation occurs very close to the surface of steel (or cartilage). While the energy is very concentrated, total amount is low enough that it needs to basically touch, or else the liquid will absorb all of it, in return for a minuscule temparature increase.
Welcome to the Straight Dope Message Boards, abandaman, we’re glad to have you here. When you start a thread, it’s helpful to other readers to provide a link to the column in question: helps keep us all on the same page, and saves searching time. I’ve added a link at the bottom of your post to the column that I assume you’re referencing. (If I’ve got it wrong, please send me an email or PM to let me know and I’ll be happy to fix.)
No biggie, you’ll know for next time. And, as I say, welcome.
Today’s column is an oldie about knuckle cracking. It reminded me of an experiment that my father did while he was a child.
When he was young, Dad’s mom, and other adults who felt obligated to comment on his life and actions, told him that if he cracked his knuckles they’d become big and ugly. Unfortunately, his mom and the other adults who feld obligated to comment on his life and actions were full of old sayings and folk wisdom that he found questionable.
He couldn’t say ‘cite?’ as that wasn’t the done thing at the time. So he determined to only ever crack the knuckles on one hand, and to compare them over time. By the time he had kids, he was able to show us both hands and tell us that those people had been wrong.
They were also wrong about putting butter on burns. And he sneered at: “Laugh before breakfast, cry before supper.” And . . . Yeah, he did have a tendency to gunny sack past resentments. He always smiled when talking about the knuckle experiment, though. You could tell that to him it was a pleasing and comforting little triumph of rationality.
There already was another thread about this article , so maybe these two could be merged 
Wait, was your father the dude who won the Ig Nobel prize?
Moderator comment: I have so merged.
Thank you for bringing that up, as I felt Cecil’s reply was somewhat lacking without that citation: scientific proof that it doesn’t lead to arthritis (at least not always).
For me it is a simple decision: cracking my knuckles relieves a feeling that my fingers are hard to move. Weighing impairment now against possible impairment later, it was an easy choice.