I've injured two knuckles trying to get them to crack when they wouldn't. Eventually I broke the habit of cracking knuckles at all to prevent further injury.
For those who read about the doctor who popped one hand with no issue is only a sample size of one and he only popped the knuckles on that hand once a day. When I started trying to break the habit I was tracking and I'd often crack a single knuckle 30+ times a day and did for 20+ years.
Crack responsibly, unlike me, and you're probably fine.
It was more like I could tell it would pop but it just needed a like more pressure. Popping knuckles stretches the tendons and my guess is since I was going it so much I stretched them so far that I had to push my fingers too far to get them to pop.
Same, when coming out of surgery on anesthesia my nurse kept trying to remove a line from my hand and i wasn't having it. Had knuckles to crack. The habit for me is just that ingrained.
I kept track of every single knuckle pop, so if I popped one whole finger it would be 3 pops. I started by measuring my baseline and then setting goals. If I made my goal that day I could do something nice for myself like play video games or get desert with my family.
Took me almost 2 years.
And for 3 to 4 years after occasionally I'd have nightmares that I started popping them again. And over that same time period as winter would approach the desire to pop them got really intense.