In rheumatoid arthritis, which is the most common site of joint involvement?

Explanation

## Most Common Sites of Joint Involvement in RA **Key Point:** The proximal interphalangeal (PIP) and metacarpophalangeal (MCP) joints of the hands are the most frequently affected joints in rheumatoid arthritis, occurring in >90% of patients with established disease. ### Pattern of Joint Involvement | Joint Site | Frequency | Characteristics | |---|---|---| | **PIP and MCP joints (hands)** | >90% | Bilateral, symmetrical; early and persistent involvement | | DIP joints (hands) | <10% | Rare; more typical of osteoarthritis | | Wrists | 80% | Common; causes carpal tunnel syndrome | | Knees, ankles, feet | 60–80% | Later involvement; weight-bearing joints | | Cervical spine | 20–30% | Late complication; atlantoaxial subluxation risk | | TMJ, shoulders | <20% | Uncommon; late manifestation | ### Clinical Significance **High-Yield:** The **symmetric polyarticular pattern affecting small joints of the hands** is a hallmark diagnostic feature of RA and distinguishes it from other arthritides. **Clinical Pearl:** The characteristic **swan-neck deformity** (hyperextension of PIP joint with flexion of DIP joint) and **boutonniere deformity** (flexion of PIP with hyperextension of DIP) develop from chronic PIP and MCP joint inflammation and destruction. ### Why Small Joints First? 1. High concentration of synovial tissue and inflammatory cells 2. Greater exposure to immune complexes and autoantibodies 3. Mechanical factors: frequent movement and stress 4. Synovial hyperplasia begins in small joints before spreading proximally **Mnemonic: HANDS-FIRST** — Hands (PIP/MCP) → Ankles → Neck → Distal (DIP avoided) → Shoulders → Feet → Inflammatory → Rarely → Spine → Temporomandibular [cite:Robbins 10e Ch 6]