Osteoarthritis
- Lesion
In osteoarthritis the joint cartilage wears and breaks down; the bone beneath thickens, grows spurs and becomes polished like ivory.
What it is
Osteoarthritis is the commonest joint disease, a degeneration of articular cartilage with reactive changes in the subchondral bone, synovium and joint capsule. It is not simple wear and tear: chondrocytes respond to mechanical and genetic stress by making matrix-degrading enzymes and inflammatory mediators, and the cartilage loses proteoglycans and type II collagen. Primary osteoarthritis appears with age in weight-bearing joints and the hands; secondary osteoarthritis starts younger after injury, deformity, obesity, crystal disease or other joint disease.
Structure
- Early: chondrocytes proliferate in clusters, matrix loses proteoglycan and water, the surface becomes fibrillated.
- Vertical fissures extend into deep cartilage; fragments break off.
- Exposed subchondral bone becomes thick and shiny (eburnation); synovial fluid forced through cracks forms subchondral cysts.
- Osteophytes (bony spurs covered by cartilage) grow at the joint margins.
- Synovium shows only mild chronic inflammation and fragments of cartilage.
Step by step
- Mechanical overload and genetic and aging factors stress chondrocytes.
- Chondrocytes produce MMPs (notably MMP-13), ADAMTS aggrecanases, IL-1, TNF and nitric oxide.
- Proteoglycans and type II collagen are degraded faster than they are made; cartilage softens and fibrillates.
- Chondrocytes die by apoptosis and repair fails; cartilage is lost down to bone.
- Bone remodels under the load: sclerosis, cysts and marginal osteophytes form; the joint becomes painful and stiff.
Clinical notes
- Deep aching joint pain worse with use and relieved by rest, short morning stiffness (under 30 minutes), crepitus and loss of motion.
- Spinal osteophytes can narrow foramina and the canal: radiculopathy, spinal stenosis and cervical myelopathy.
- No systemic features; ESR and CRP normal; synovial fluid non-inflammatory.
- Treatment: weight loss, exercise, analgesics, and joint replacement for end-stage disease.
Test yourself
Think of the answer, then tap the question to see it.
What is eburnation?
Polished, ivory-like subchondral bone exposed after loss of the articular cartilage.
Which finger joints form Heberden nodes?
The distal interphalangeal joints.
Which enzymes degrade cartilage in osteoarthritis?
Matrix metalloproteinases (especially MMP-13) and ADAMTS aggrecanases made by chondrocytes.
How long does morning stiffness usually last in osteoarthritis?
Less than about 30 minutes, unlike the longer stiffness of rheumatoid arthritis.
Elsewhere in DurgiPedia
- Cartilage: hyaline, elastic, fibrocartilage
- Synovial joints: capsule, synovial membrane and articular cartilage
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Primary Osteoarthritis (StatPearls (NCBI Bookshelf), 2025); Osteoarthritis | OA | MedlinePlus (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.