[The only definitive finding is a fracture of the first rib.]

Could they tell if the fracture was fresh or long ago healed?
Did it seem deformed compared to the other side?
Are you sx worse on that side- that could tell if it might be a factor or not..

Generally is your head or shoulders forward of the body when viewed from side by someone? Same for rolled or hunched shoulders..
If so, that posture will crowd the space we need to avoid TOS , so it can be a big factor.

Any past whiplash, sports injuries , head/shoulder hits /falls etc?
some info - http://www.upcspine.com/self.htm