@NOEngineer:
My father and at least 3 of my four brothers crack many joints, mainly neck, knuckles, ankles, and back. We also have other common traits (all engineers with very high intelligence, all have green/blue eyes despite brown hair and easily tanned skin).
I have the worst cracking problems of all the family. My ankles crack whenever I wake up (involuntarily), and my range of motion becomes limited if I don't crack knuckles, neck and ankles several times per hour. The only joints that rarely crack are elbows, shoulders, and hips.
I was diagnosed with hyperactivity when a child (before ADHD was cool) and am now in my late 40s. Been cracking my neck since my early 20s, either by manual cranking or accelerated head-spinning. No paralyisis yet. My knees are starting to experience sharp pains. I am the only family member who is significantly (40 - 50 lbs) overweight.
My nieces crack knuckles. I have kids 3 and 6 and hear their joints crack from time to time during active play, but have tried to discourage any purposeful cracking on their part.
My brother got "treatment" for neck cracking for a while during Navy training that consisted of antidepressants. Seemed to help temporarily.
Not aware of any issues on my mother's side. My cousins/uncles aren't close so I haven't noticed/asked about their crack issues…..
NOEngineer, thank you for your detailed report, which is kinda backping up a genetic correlation.