As a knuckle cracker myself, it's certainly relieving that there's no evidence of degenerative harm even though there are apparently a few cases we'd probably see it if it occurred. However, the reduced grip strength (admittedly small N) is notable. If that is a change that occurs on a relative short timescale (i.e., starts when you start cracking your knuckles and stops when you stop), it's potentially feasible to study with an RCT. I bet you could even estimate compliance with knuckle-cracking instructions using something like a FitBit.