## Primary Pathological Feature of Osteoarthritis **Key Point:** Osteoarthritis is fundamentally a degenerative joint disease characterized by progressive loss of articular cartilage and reactive bone changes. ### Pathological Hallmarks The cardinal pathological features of osteoarthritis include: 1. **Articular cartilage degradation** — fibrillation, fissuring, and ulceration of hyaline cartilage 2. **Osteophyte (bone spur) formation** — reactive new bone formation at joint margins 3. **Subchondral bone changes** — sclerosis and cyst formation 4. **Synovial changes** — mild chronic inflammation (secondary, not primary) **High-Yield:** Unlike rheumatoid arthritis (which is primarily inflammatory), osteoarthritis is a **mechanical degenerative process**. The cartilage loss is due to imbalance between mechanical stress and the cartilage's capacity to repair itself. ### Comparison: OA vs. RA | Feature | Osteoarthritis | Rheumatoid Arthritis | |---------|---|---| | **Primary pathology** | Cartilage degeneration + osteophytes | Synovial inflammation + pannus | | **Bone erosion pattern** | Marginal (at osteophytes) | Central (juxta-articular) | | **Inflammatory markers** | Normal or mildly elevated | Markedly elevated (ESR, CRP) | | **Systemic features** | Absent | Present (fever, malaise, nodules) | **Clinical Pearl:** Osteophytes are a hallmark radiological finding in OA and represent the joint's attempt at stabilization through new bone formation at areas of cartilage loss. [cite:Robbins 10e Ch 26] 
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