Table 1 Stages of osteoarthritis

Feature	Reversible injury	Osteoarthritis	Ageing
Cartilage mass	Hypertrophy	Hypertrophy, erosion	No Change
Cartilage topographic distribution	Focal	Focal. Heterogeneous	General, all layers
Cartilage water	Oedema	Oedema	Dehydration
Cartilage collagen	Reversible deformation	Degradation	Increased advanced glycation end products
Cartilage proteoglycan	Reversible depletion	Irreversible depletion	Reduced synthesis
Cartilage matrix degeneration products	Resorption	Accumulative, collagen, proteoglycan	Accumulative: oxidation. Glycation, amyloid
Cell activity	Reversibly increased	Increased activity and proliferation	Reduced
Synovium	Mid focal superficial inflammation	Mid focal superficial inflammation	Atrophy
Bone	No Change	Subchondral remodelling	Osteopenia

Reproduced with permission and copyright© of the British Editorial Society of Bone and Joint Surgery. Pollard et al, 2008. The assessment of early osteoarthritis. J Bone Joint Surg Br;90-B:411–21.