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White colour is normal articular cartilage?
Where is articular cartilage thickest?
In the young and at sites of maximal weight bearing
True or false: articular cartilage has a nerve, blood and lymphatic supply?
What does articular cartilage merge with at its margins?
It merges with a periosteal surface lines by fibrous tissue that is continuous with the synovial membrane
How does articular cartilage get its nutrition?
Nutrients diffuse into the articular cartilage from the synovial fluid and subchondral vessels.
What type of collagen in mainly present in articular cartilage?
Type II collagen
Describe the different layers of articular cartilage and their functions
- Superficial layers resist shearing forces (layers are being shifted relative to one another)
- Middle layers are involved in shock absorption
- Calcified cartilage attaches articular cartilage to bone by its irregular (interlocking) interfaces
What is the tidemark, in articular cartilage?
The tidemark is the boundary between uncalcified articular cartilage and the calcified cartilage
Under what circumstances is cartilage injury painful?
Only when the subchondral bone or synovium (tissues around the joint) are involved
True or false: cartilage does not participate in inflammatory responses?
True - it is only affected by inflammation in the synovium, subchondral bone or growth cartilage
Give examples of things that can cause a sterile injury to cartilage?
Trauma, joint instability, lubrication failure
Describe the effect of repetitive stress on cartilage
Repetitive stress can damage both the matrix and chondrocytes, leading to inappropriate cellular responses, chondrocyte death and therefore a viscous cycle of injury - i.e. accumulation of micro damage
True or false: cartilage has a minimal capacity for repair?
True - cartilage has a limited response to injury
Describe cartilage fibrilation, erosion and ulceration
- Fibrilation - this is when proteoglycans are lost, collagen fibres condense and fray
- Erosion - this is when there is damage but it does not penetrate the subchondral bone
- Ulceration - this is when the full thickness of cartilage is lost. Areas of ulceration become filled with vascular fibrous tissue.
During cartilage ulceration exposed subchondral bone develops increased density due to increased mechanical use, what is the term for this?
Outline the steps in DJD
- Chondromalacia (softening)
- Erosion and fibrillation
What are osteophytes?
During what disease is there often the formation of osteophytes? What initiates their formation?
DJD. It is initiated by joint instability and/or inflammatory cytokines.
What diagnostic test is important for diagnosing DJD?
What is pannus?
Inflammatory disease - it is a fibrovascular and inflammatory tissue that arises in the synvoium and spreads over articular cartilage.
What is osteochondrosis?
A group of lesions in young animals where there is focal or multifocal failure of endochondral ossification at the metaphyseal growth plate and articular-epiphyseal complex. In small animal medicine it is a big cause of DJD in older animals.
What are the different types of osteochondrosis?
- Osteochondrosis latens - this is the first lesion where there is necrosis of blood vessels in the epiphyseal cartilage of the articular-epiphyseal complex. These are microscopic lesions.
- Osteochondrosis manifesta - when the ossification front reaches this area of necrosis and there is a grossly visible area of necrotic epiphyseal cartilage.
- Osteochondritis dissecans - when clefts can form in the osteochondrosis lesion of the AE complex. The overlying cartilage fractures and flaps can form.
What is a 'joint mouse'?
When a flap of articular cartilage breaks off during osteochondrosis and it 'lives' in the synovial fluid