Can any doc tell me what's the best otc pain medicine for old broken limb injury?

Open injury: I assume that you have an open wound. The chances of infection are very high if the skin is broken. First thing to do is (if the wound is small and not bleeding much) to clean it with antiseptic solution and apply antibiotic ointment and a bandage. If the wound is large, please go to an urgent care center where they can properly assess it and treat it. You can take acetaminophen for pain.

Old fracture: Nonsteroidal anti-inflammatory drugs (NSAIDS) can help with both pain relief and in reducing inflammation. Examples are ibuprofen (like Advil, Nuprin or Motrin), Naproxen sodium (like Aleve, (naproxen) Naprosyn, Anaprox) or Asprin (such as Bayer, Ecotrin, Ascriptin). Avoid NSAID's if pregnant or allergic to them. In that situation can consider acetaminophen.