Can an X-ray really diagnose arthritis? My doctor says my X-ray shows signs of osteoarthritis. I thought arthritis was when there’s not enough cartilage in your joints. How can you see that on an x-ray?

Yes, to some degree. Xrays cannot show cartilage, however, loss of cartilage is reflected in narrowing of the joint space where the cartilage should be. Decreased thickness of bone (demineralization) around joints can suggest inflammation. Erosions or holes in the bone and where they are located can aid in diagnosing types of inflammatory arthritis.
X-rays . X-rays can not only diagnose arthritis, they can also differentiate among several different types (rheumatoid, degenerative, autoimmune, infectious, etc). The word arthritis is latin for "inflammation of the joint, " and though damage to the cartilage is often present, it is not always seen in every type of arthritis, and certainly not to the same degree. Sometimes an x-ray alone is not enough, and blood tests are required. Still, they are an excellent screening test and often do stand alone in making a specific diagnosis of arthritis.