The medical world has developed it's own language tapping other languages for it's own terminology system. One could say that this terminology is used to help define and differentiate different issues, conditions, problems more clearly and specifically. One the other side, one could also say that word choices in other languages identifying problems are used to sound more sophisticated and scary at the same time to strike terror into the heart of the patient so that they buy into whatever they are told good or bad, accurate or not and or so the fear plus thought actually manifests a greater problem or even generates a new problem if they never even had such a problem in the first place.
Then again it's just much more neat and organized to say "osteoporosis" vs. "degenerative bones condition" or "bone becoming weak and brittle condition"
Osteo means bone and is used as a prefix for bone conditions as defined by modern medicine.
Medical Definition of Osteo- (prefix)
Osteo- (prefix): Combining form meaning bone. From the Greek "osteon", bone. Appears for instance in osteoarthritis, osteochondroma osteodystrophy, osteogenesis, osteomyelitis, osteopathy, osteopetrosis, osteoporosis, osteosarcoma, etc. from http://www.medicinenet.com/script/main/art.asp?articlekey=4674
indicating bone or bones: osteopathy
from Greek osteon