I'd like to know the mechanisms which mediate the pain response in rib fractures?

Bones have their own nerves. From Nursing school 1972

Um…yeah, nerves. Bones do have nerves and there are medications and treatments out there to stop bone pain, but it’s usually used on cancer patients. Quadramet is a nuclear medicine that helps reduce bone pain caused by bone cancer and an OSU pharmacist (which I do not believe) said they don’t even know how or why it works, but it does.

I don’t think you are getting the answers you’re looking for. Try rephrasing the question and give some more info as to why you think it could be the thoracic nerves.