What is the main difference between osteoarthritis & osteoporosis?

Bone structure. Osteoporosis is thinning of the bone which can lead to fractures from minor falls. Osteoarthritis is wearing of the cartilage on the end of the bone which leads to pain and disability.
Much. One is joint inflamation osteoporosis is soft bone they only begin with the same four letters otherwise they are completley unrelated they both occur in older people.