## Histopathological Features of Osteoarthritis **Key Point:** The cardinal histopathological finding in osteoarthritis is progressive loss of hyaline articular cartilage with fibrillation, thinning, and eventual exposure of the underlying subchondral bone. ### Sequence of Cartilage Degeneration 1. **Early changes:** Superficial fibrillation and loss of cartilage matrix 2. **Progressive loss:** Thinning of cartilage layer with cleft formation 3. **Advanced stage:** Complete cartilage loss exposing subchondral bone plate 4. **Bone response:** Subchondral sclerosis and osteophyte (bone spur) formation at joint margins ### Associated Features - **Synovial changes:** Mild chronic inflammation (NOT pannus formation) - **Bone changes:** Subchondral cysts, eburnation (polishing of exposed bone) - **Marginal changes:** Osteophytes and bone proliferation **High-Yield:** Unlike rheumatoid arthritis (which shows pannus), osteoarthritis is primarily a **degenerative disease** with cartilage loss as the dominant pathology, NOT an inflammatory disease. **Clinical Pearl:** The fibrillation of cartilage surface is one of the earliest detectable changes and can be seen on arthroscopy before radiographic changes appear. [cite:Robbins 10e Ch 27] 
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