While X-rays are used to reveal the appearance of osteoarthritic joints to diagnosticians, there is not always a direct correlation between what the X-rays show and the symptoms of osteoarthritis that a patient is experiencing.
By age 40, many people have some evidence of osteoarthritis on X-rays. About 80% of people 55 and older have X-ray evidence of osteoarthritis and approximately 60% develop symptoms.
X-rays of osteoarthritis do not detect early cartilage abnormalities. Also, X-rays can show mild osteoarthritis (i.e., minor abnormalities) while a patient may be experiencing severe symptoms.
Conversely, an X-ray may show changes that suggest advanced or severe osteoarthritis in someone who is having few no symptoms. Early cartilage abnormalities are detectable with magnetic resonance imaging but MRIs are rarely used for routine diagnosis of osteoarthritis.
Though symptoms may not directly correlate with X-ray evidence of osteoarthritis, it is typical for a doctor to order X-rays of a painful joint. There are certain X-ray findings that can help doctors and radiologists formulate impressions and diagnose osteoarthritis. The findings include the following.
Joint Space Narrowing
Osteoarthritis causes deterioration of the joint structures. Wearing away or deterioration of articular cartilage leads to narrowing of the joint space (i.e., the space between the end of bones in a joint).
Progressively smaller joint space suggests worsening of osteoarthritis. Joint space loss is usually not uniform within the joint. “Bone-on-bone” suggests there is no joint space left.
Development of Osteophytes
Osteophytes, also called bone spurs, are protrusions of bone and cartilage. The bony projections are commonly seen in areas of a degenerating joint and can be seen on X-rays. Osteophytes, which typically develop as a reparative response by remaining cartilage, cause pain and limited range of motion in the affected joint.
Subchondral Sclerosis
Subchondral bone is the layer of bone just below the cartilage. Sclerosis means that there is a hardening of tissue. Subchondral sclerosis is seen on X-ray as increased bone density, frequently found adjacent to joint space narrowing. The degeneration of bone that occurs in osteoarthritis causes the bone to turn into a dense mass at the articular surfaces of the bone.
Subchondral Cyst Formation
Subchondral cysts are fluid-filled sacs which extrude from the joint. The cysts contain thickened joint material, mostly hyaluronic acid. Traumatized subchondral bone undergoes cystic degeneration.
Subluxation
Subluxation can also be seen on X-ray as a possible consequence of osteoarthritis. Subluxation is a partial dislocation of a bone.
