Causes of injury
- Trauma
- Instability
- Lubrication failure
- Infectious organisms
- Immune-mediated disease
Reaction to injury
- Articular cartilage has limited ability to regenerate
- Superficial defects are long standing
- Chondrocyte hyperplasia is ineffective at filling the defect
- Non-painful
- Defects reaching subchondral bone
- Filled with vascular fibroous tissue undergoing metaplasia into cartilage
- Painful
- Fibrillation - loss of proteoglycans -> condensation of collagen fibres -> fraying of surface
- Eburnation - loss of articular cartilage -> exposure of subchondral bone -> becomes dense and polished
- Synovial membranes respond by:
- Villous hypertrophy
- Hyperplasia