A 62-year-old woman from Delhi presents with a 3-year history of progressive pain and stiffness in both knees, worse in the morning and after prolonged sitting. She reports morning stiffness lasting 15–20 minutes. On examination, there is crepitus on passive knee flexion, mild effusion, and reduced range of motion. X-ray of both knees shows joint space narrowing, osteophytes, and subchondral sclerosis. Her ESR is 12 mm/h and CRP is 2 mg/L. What is the most likely diagnosis?

Explanation

## Diagnosis: Osteoarthritis ### Clinical Features Supporting OA **Key Point:** Osteoarthritis is a degenerative joint disease characterized by progressive cartilage loss, osteophyte formation, and subchondral bone changes. ### Diagnostic Criteria Met | Feature | Finding | Significance | |---------|---------|---------------| | **Age & onset** | 62 years, 3-year progressive course | OA typically affects older adults; gradual onset | | **Morning stiffness** | 15–20 minutes | Brief stiffness typical of OA (RA: >1 hour) | | **Joint involvement** | Bilateral knees (weight-bearing) | OA favours weight-bearing joints | | **Crepitus** | Present on passive motion | Cartilage irregularity and osteophytes | | **Inflammatory markers** | ESR 12, CRP 2 (normal) | OA is non-inflammatory; RA would show elevation | | **X-ray findings** | Joint space narrowing, osteophytes, sclerosis | Pathognomonic for OA | ### Pathophysiology 1. **Cartilage degradation** → loss of articular surface 2. **Osteophyte formation** → bone remodelling at joint margins 3. **Subchondral sclerosis** → bone thickening beneath cartilage 4. **Synovial inflammation** (mild) → crepitus and effusion **High-Yield:** The combination of **normal inflammatory markers + radiographic osteophytes + weight-bearing joint involvement + brief morning stiffness** is diagnostic of primary OA. **Clinical Pearl:** Bilateral knee OA in a 62-year-old woman is extremely common; it is the leading cause of disability in older adults in India. ### Why OA, Not Other Diagnoses? - **RA:** Would show prolonged morning stiffness (>1 hour), elevated ESR/CRP, symmetrical small joint involvement (hands), and rheumatoid factor positivity. - **SLE:** Would present with systemic features (rash, photosensitivity, renal involvement), positive ANA, and low complement levels. - **AS:** Would show axial spine involvement, HLA-B27 positivity, and inflammatory markers elevation.