A 62-year-old woman presents with progressive pain and stiffness in both knees for 8 months. Clinical examination reveals crepitus, joint line tenderness, and mild valgus deformity. She has morning stiffness lasting 15 minutes. Which investigation is most appropriate to confirm the diagnosis and assess severity of osteoarthritis?

## Investigation of Choice for Osteoarthritis Diagnosis **Key Point:** Plain radiographs are the gold standard first-line imaging for diagnosis and severity assessment of osteoarthritis. They are cost-effective, widely available, and sufficient for clinical decision-making in most cases. ### Why Plain Radiographs? 1. **Diagnostic criteria on X-ray:** - Joint space narrowing (loss of cartilage) - Osteophyte formation (bone spurs) - Subchondral sclerosis (increased bone density) - Subchondral cysts 2. **Kellgren-Lawrence grading system** (0–4) uses radiographs to stage OA severity and guide treatment escalation. 3. **Cost-effectiveness:** Minimal radiation, inexpensive, reproducible for follow-up. ### Radiographic Views for Knee OA | View | Purpose | |------|----------| | **AP (standing)** | Assess medial and lateral compartment joint space | | **Lateral** | Evaluate patellofemoral compartment and posterior osteophytes | | **Skyline (Merchant)** | Assess patellofemoral OA and patellar tracking | **Clinical Pearl:** Morning stiffness <30 minutes and crepitus are classic OA features; radiographs will confirm structural changes. **High-Yield:** Kellgren-Lawrence Grade 2 (minimal OA) may show only questionable osteophytes; Grade 3–4 shows definite joint space narrowing and osteophytes — this guides conservative vs. surgical management. ### When to Use Advanced Imaging - **MRI:** Reserved for atypical presentations, suspected meniscal or ligamentous injury, or when radiographs are inconclusive. - **Contrast-enhanced MRI:** Not routine for uncomplicated OA diagnosis. [cite:Robbins 10e Ch 26]