There's no evidence that knuckle cracking causes arthritis. But it may cause temporary soreness of the joint.
Knuckles are the joints that connect your fingers to your hand. These joints are surrounded and lubricated by synovial fluid, a thick, clear liquid. When you crack your knuckles, you're causing the bones of the joint to pull apart. This causes a gas bubble to form in the joint. The cracking or popping sound you hear is the breaking of the adhesive seal in the joint. It may take awhile for the joint to reseal before you can crack your knuckles again.
I have severe arthritis and the knuckles on my hands are very swollen but I have never cracked my knuckles ...ever.