Detecting severed joints?

Hey me again with another question.

How would I go about detecting if a joint is severed or not?  And also, how would I detect what node this joint was attached too?  I am making a snake composed of spheres, and I want it so that if a part of the tail gets severed from the head, it gets deleted to preserve cpu.  Unfortunately I have no idea how to go about detecting this, let alone telling what node's joint it was that severed.  Any advice?