Radiological features of osteoarthritis in the knee include joint space narrowing, subchondral sclerosis, and osteophyte formation. Which radiographic finding distinguishes osteoarthritis from rheumatoid arthritis affecting the same joint?

• A Periarticular osteoporosis
• B Preservation of bone density with subchondral sclerosis and osteophytes ✓
• C Marginal erosions at joint margins
• D Symmetrical joint space narrowing

Explanation

Osteoarthritis is characterised by joint space narrowing (asymmetric, usually weight-bearing area), subchondral sclerosis (bone remodelling in response to load), osteophyte formation (marginal bony outgrowths), subchondral cysts, and preserved — sometimes increased — bone density. Rheumatoid arthritis, in contrast, shows periarticular osteoporosis (A), marginal erosions (C), symmetric joint space narrowing (D), and no osteophytes. The triad of subchondral sclerosis + osteophytes + preserved bone density is pathognomonic of OA.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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