What is the difference between osteoporosis and osteoarthritis?

Very different. Osteoporosis refers to thinning of the bones and generally affects the whole skeleton. It is a painless process unless a fracture occurs. Osteoarthritis refers to a painful joint disease due to narrowing of the joints so bone may be rubbing on bone. It may commonly affect the joints of the hips, knees, or hands.
Pain. Osteoporosis is a painless decrease in the minerals within bone causing it to lose density where arthritis is inflammation of a joint from any number of sources.

Related Questions

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. Read more...
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. Read more...