My husband had a car accident when he was a child over 30 years ago and due to financial reasons his family was never able to get him medical attention. So now that he is an adult his right thumb on his right hand is deformed (no problem about that) but is infected really badly and he is in a lot of pain. What kind of doctor should I look for to treat him?

If it is just an infection a GP or family doctor should take care of it.

I agree that a GP is the place to start. If the GP can't treat the infection, he/she will refer you to the right specialist.