The first paper states We carried out a "before-after" quasi-experimental study not really reassuring.
The second seems to have been done more professionally but unless they can state categorically that all the patients in both groups were given exactly the same treatments, drugs, dosages, physio etc. as well as the vit c or placebo there are too many variables to really come to a positive conclusion regarding the use of Vit c
That doesn't mean it isn't worth trying but it has to happen at the time of the fracture so for many of us it's too late.