Wrist locks are allowed, but I don't think I've ever seen an MMA fight end via wrist lock. Small joint manipulation (individual fingers, individual toes) is not allowed. All other joints - neck, elbows, knees, ankles, wrists - are allowed.
It seems the goal is to prevent broken fingers and toes. Would manipulating 4 fingers simultaneously (to achieve wrist/elbow/shoulder lock) violate the small joint manipulation rule?
That's valid, as that's seen as manipulating the hand. For example, to defend a rear choke attempt, people will grab the meat of the hand. Grabbing an individual finger would not be okay. However, if you're going for another kind of lock, and the only control you have is the four fingers (no thumb, not applying pressure at base of hand), you're probably not going to succeed.
