Many thanks for posting the question via my forum. Before answering, I would like to remind you that , my post is like a guide for you. But to come to a pinpoint diagnosis, I will repeatedly as you to visit the treating doctor or meet a good consultant.
RA is an auto-immune disease and the main cause if it is IDIOPATHIC (unknown origin).
There are various triggers suspected to be associated with it, however the proof is not present.
In your case, i would no co-relate it with the fracture event. The sudden origin of RA, can be purely Idiopathic.
70% cases have blood reports positive of RA where as 30% reports shows negative blood tests. So don't think , if the reports are negative, then there can be no probability if RA.
The main problem with this disease is that it causes auto-inflamation of the various joints, which causes slow joint destruction, by acting over the cartilage, which slowly leads to nodule formation, over the small joints (which you are experiencing).
Please feel free to discuss more with me as a fresh post.
Also , if you are satisfied with my answer, do refer your friends also.
I have got other forums also (Arthritis , Back and Neck Surgery, Back and Spine Surgery, Brain Tumor Forum, Headaches , Hip Surgery, Knee Surgery , Neurology/Neurosurgery, Rheumatoid Arthritis. Trigeminal Neuralgia), where you can post other related queries