If you see an X-ray of a healed fracture, you'll usually see a jagged line through the bone of greater density (where the fracture was) and a slight "callus" - could present as a dip or a bump in the surface - where the surface knit together.
Since there's a change in density, it won't expand or contract at the same rate as the surrounding bone. Therefore, you'll get a strong ache there (or a sharp pain) as a result.
This can also apply to screws, pins, and plates - same reason (the metal is a different density from the bone. If there are pins along the length of the bone, you have to deal with the fracture that allowed them to be inserted as well.)
I note this more when the barometric pressure drops than when it rises - I usually have a good 48 hours' warning of impending rain. I also have extensive fractures, especially in my face - there are some days where I just hurt too damned bad to get out of bed.
Scar tissue can cause much the same problem, just to a lesser extent.
If you have issues with nerve impingement (my shoulder and neck are good examples - fracturing C2 and C5 didn't help,) you'll note weather-related trouble there as well.
It also has an effect on arthritic joints - like L4/L5 and L5/S1 for me (results of a life lived hard.)