Tail Bone Exposed!

My neighbor's cat likes to hang around my house as we have 3 cats that he can play with.  However, the other day I saw a little white stick sticking out of the tip of his tail.  When I touched it, he would nudge away from me.  I held him down and found out that it's HIS TAIL BONE!  It looks as if the poor guy did something that made his bone pierce his skin and stick out.  The skin has scabbed over, there's quite a bit of fur missing around the area and the bone is sticking out quite a bit.  Every once in a while he'll bite on the bone and try and rip it out.

He is still very playful, purs and cuddles a lot, eating normally and sleeping normally.  However, whenever he is awake and not doing any of these activities, he is sitting there licking his poor tail.

Is this possibly a skin disease that ate away the skin around the bone?  I don't want him around my cats if he's contagious...

For those who are concerned: I have been waiting for his owners to be home so I can take him over there and ask them to get him the help he needs.  If I don't see them for a few more days, I'm seriously considering taking him to the vet myself even though I don't have much money at the moment for something like this.  I heard it may have to be amputated?? 

The cat needs to see a vet ASAP.  If I saw one like that round here, in the UK, and had any idea where it lived I'd ring the RSPCA.  Since you haven't put which country you are in I assume the US.  Hopefully some other US folks will be able to advise further.

That really does need to be looked at by a vet. I found a kitten one time with half of his tail chopped off, and even with a clean cut, I still took him immediately to a vet to have it looked at. If it is an injury, he needs antibiotics. If it is a skin illness, he needs medication. If you don't find your neighbors soon, call your vet if you have one and ask for advice.