This dog needs to be examined by a veterinarian to determine if this is related to the old injury or is a new problem.  Especially if this is related to the old injury your veterinarian may want to prescribe some non-steroidal anti-inflammatories for pain and swelling.  They can also give you a dose of aspirin to use if appropriate.  Do NOT give your dog any  human pain medication without consulting your veterinarian.  Not all human medications are safe for dogs and the ones that are safe most often are dosed differently.