How can you differentiate osteoarthritis from inflammatory arthritis on imaging?

• A. OA shows joint space narrowing with osteophytes and subchondral sclerosis; inflammatory arthritis shows erosions and more uniform joint space narrowing with soft tissue swelling.
• B. Inflammatory arthritis shows osteophytes and sclerosis; OA shows erosions.
• C. OA has erosions; inflammatory has osteophytes.
• D. Both have identical imaging findings.

Answer: (A)

Imaging distinguishes these two by the pattern of joint damage seen. Osteoarthritis reflects wear-and-tear changes, so you expect joint space narrowing that is often asymmetric, along with osteophyte formation (bone spurs) and increased subchondral sclerosis from bone thickening beneath the cartilage. Erosions, which are breaks in the bone at the joint margins, are not typical of OA.

Inflammatory arthritis, by contrast, shows synovial inflammation on imaging. This tends to produce soft tissue swelling around the joints and bone erosions at the joint margins due to inflammatory destruction. When joint space narrowing is present, it can be more uniform across multiple joints rather than localized to a single compartment.

So the combination described—OA with joint space narrowing plus osteophytes and subchondral sclerosis, versus inflammatory arthritis with erosions and soft tissue swelling—is the characteristic way to differentiate them on imaging.