A 68-year-old man from rural India presents with bilateral hand pain and stiffness, worse in the morning. Examination reveals Heberden's nodes and Bouchard's nodes. Which is the most common cause of osteoarthritis in the hand?

Explanation

## Most Common Cause of Hand Osteoarthritis **Key Point:** Primary (idiopathic) osteoarthritis is the most common cause of hand OA, accounting for >90% of cases. It is a degenerative joint disease without an identifiable secondary cause. ### Classification of Hand OA by Etiology | Cause | Frequency | Features | Risk Factors | |-------|-----------|----------|---------------| | Primary (idiopathic) | >90% | Heberden's/Bouchard's nodes, DIP/PIP involvement | Age, female sex, genetic predisposition | | Post-traumatic | 5–10% | History of fracture/injury, asymmetric pattern | Prior hand trauma, occupational stress | | Rheumatoid arthritis | Rare in hand OA | MCP involvement, systemic symptoms, RF/anti-CCP | Autoimmune disease | | Hemochromatosis | Rare | 2nd/3rd MCP joints, systemic iron overload | Genetic mutation (HFE) | **High-Yield:** Hand OA is the **most common site of OA overall** across all joints in the body. The **distal interphalangeal (DIP) joints** are most frequently affected, followed by the proximal interphalangeal (PIP) joints and the first carpometacarpal (CMC) joint of the thumb. ### Clinical Features of Primary Hand OA 1. **Heberden's nodes:** Osteophytes at DIP joints (pathognomonic) 2. **Bouchard's nodes:** Osteophytes at PIP joints 3. **Morning stiffness:** Usually <30 minutes 4. **Bilateral and symmetrical:** Typical distribution pattern 5. **Female predominance:** 10:1 female-to-male ratio **Clinical Pearl:** The presence of Heberden's nodes is almost diagnostic of primary hand OA. These are bony enlargements at the DIP joints and are considered a hallmark of idiopathic OA. **Mnemonic:** **HOP** = **H**eberden's nodes (DIP), **O**steoarthritis (primary), **P**rimary cause (idiopathic) ### Why Other Causes Are Rare in Hand OA - **Rheumatoid arthritis:** Affects MCPs more than DIPs; associated with systemic inflammation, RF/anti-CCP positivity - **Post-traumatic OA:** Requires documented prior injury; asymmetric pattern - **Hemochromatosis:** Rare; involves 2nd/3rd MCP joints preferentially; associated with systemic iron overload **Warning:** Do not confuse primary hand OA with rheumatoid arthritis. RA is inflammatory (elevated ESR/CRP, positive RF/anti-CCP), affects MCPs, and has systemic features. Hand OA is degenerative, non-inflammatory, and affects DIPs.