| Feature | Osteoarthritis (OA) | Rheumatoid Arthritis (RA) |
|---|---|---|
| Mechanism | Mechanical “Wear & Tear” | Autoimmune (Pannus) |
| Stiffness | < 30 min (Worse w/ use) | > 1 hr (Better w/ use) |
| Symmetry | Asymmetric | Symmetric |
| Key Joints | DIP (Heberden), PIP, Knees | MCP, PIP, Wrist (Spares DIP) |
| Labs | Normal | +Anti-CCP (Specific), +RF, ↑ ESR |
| X-ray | Osteophytes, Sclerosis | Marginal Erosions, Osteopenia |
| Treatment | NSAIDs, Acetaminophen | DMARDs (Methotrexate) |
1. Stiffness
- OA (<30m): “Gelling.” Synovial fluid gets thick at rest. Movement quickly warms and lubricates it.
- RA (>1h): Edema. Inflammatory fluid pools during sleep. Takes time to mechanically pump/drain the boggy joint.
2. Pain
- OA (Worse w/ use): Mechanical. Bone-on-bone friction compresses exposed nerve endings.
- RA (Better w/ use): Washout. Movement flushes out stagnant inflammatory cytokines and fluid, relieving pressure.
3. Pathology
- OA (Osteophytes): Construction. Bone grows spurs to widen surface area and stabilize the failing joint.
- RA (Erosions): Destruction. Pannus (granulation tissue) releases enzymes/RANKL that eat into the bone.