Pathological Features of Osteoarthritis : Wheeless' Textbook of Orthopaedics

- Discussion:
- osteoarthritis represents a gradual processes of destruction & regeneration;
- early in dz, articular cartilage loses its glistening appearance;
- later on surface layers flake off while deeper layers develop longitudinal fissures, process termed fibrillation;
- cartilage becomes thin and sometimes denuded;
    - collagen fibre structure is altered and the number and quality of proteoglycan aggregates decreases
    - chondrocytes isolated from patients with OA produce 50-fold more PGE2 than chondrocytes from patients without OA;
    - prostaglandin-stimulated release of matrix metalloproteinases: may lead to cartilage degradation;
    - subchondral bone:
- becomes thickened, sclerotic, & polished (eburnation);
- subchondral bone displays thickened trabeculae and microfractures;
- tidemark is disrupted by vessels from the subchondral layer;
- cysts:
- may be seen in subchondral bone;
- cysts may arises from increases in intrasynovial pressure;
- osteophytes:
- spurlike bony outgrowths covered by hyaline cartilage, may develop at margins of joint & progressively enlarge;
- small bits of cartilage-covered bone, known as joint mice, may actually break off into the joint;

- Histology:
- see: articular cartilage
- superficial zone demonstrates earliest changes;
- there is a diminution of chondrocytes in superficial zones;
- cartilage matrix loses its ability to stain for proteoglycans with alcian blue or safranin-O;
- deeper chondrocytes demonstrate proliferation in clusters (brood capsules);
- capillary buds penetrate the layer of calcified cartilage;
- newly formed sements of cartilage push up from below;
- tidemark:
- demarcation between calcified and noncalcified cartilage;
- becomes split & reduplicating tidemark;
- synovium: becomes hypertrophied and thrown into villose folds;
- may see infiltration with plasma cells, and lymphocytes;
- syovial hypertrophy may be involved in producing joint pain by increased synovial fluid production and increased intra-articular pressure