Cartilage Aging

Question 1

What is O?

Answer 1

• progressive and permenant degeneration of the articular cartilage

Question 2

How does OA differ from rheumatoid arthritis?

Answer 2

> OA
- lacks most common classical signs of inflam
- serology negative for IgM rheumatoid factor 
- fibrillation and softening of cartilage surface on arthroscopy
- narrowed joint space
- osteophyte formation 
- sunchondral bone sclerosis 
-crepitus 
> rheumatoid
- more d/t inflamed synovium 
- more cytokines inovled
- not common in animals

Question 3

Which cytokines are especially involved in cartilage degradation?

Answer 3

• IL1b
• TNFa
  > enhance production of enzymes -> cartilage degradation

Question 4

What forms of OA is most common in animals cf. humans?

Answer 4

animals 2* to trauma

- idiopathic in humans

Question 5

What type of joints are ^ risk for OA?

Answer 5

• high mobility eg. MCP

Question 6

What type of dogs are ^ risk OA?

Answer 6

• older
• greyhounds
• large breeds
• lumbosacral disk degeneration ^ freq in GSDs

Question 7

What other species get OA?

Answer 7

Cats - esp older and in appendicular joints

- pigs get OCD

Question 8

Is OA always preceded by OCD?

Answer 8

NO

Question 9

What are the 4 main theories of aging?

Answer 9

> evolutionary theories
- disposable soma/antagonistic pleiotropy/mutation accumulation
molecular thoeries
- error catastrophe/somatic mutation/gener regulation/expression
cellular theories
- senescence/apoptosis/wear and tear/ free radicals
systems theories
- neuroendocrine/immunologic

Question 10

What is disposable soma theory?

Answer 10

• repair mechanisms only maintained until the organism has reproduced
• balance repair and energy resources

Question 11

WHat is the Stochastic theory of aging?

Answer 11

= error catastrophe

• randomevents at cellular/molecular level drive aging
• mutated proteins will be degraded but if the protein is itself needed for genetic components this will ^ risk of further muations

Question 12

Functino of cartilage?

Answer 12

• template for bone growth (foetal)
• resists compression (weight-bearing)
• resilience
• support
• flexibility
• lubrication and movement at diarthrodial joints

Question 13

What are the major components of hyaline cartilage ECM

Answer 13

• Collagen type 2
• proteoglycans (mostly aggrecan)
• water
• some chondrocytes (otherwise avascular, aneural, low cell density)

Question 14

How does healthy cartilage behave under compressive loading and unloading?

Answer 14

• intstant deformation when loaded
• creep deformation and plateaux
• instant relaxation when unloded
• stress relaxtion

Question 15

How does UNhealthy cartilage behave under compressive loading and unloading?

Answer 15

More deformation on loading

• either excessive rebound when unloaded (if slightly affected)
• or insufficient rebound when unloaded (with OA)

Question 16

How do GAGs attract water?

Answer 16

Na and Cl attracted to balance charges, water by osmosis

Question 17

What hydrostatic pressure is hyaline cartilage under?

Answer 17

-similar to car tyre pressure!!

Question 18

What is mechanical behaviour determined by? How does OA affect this?

Answer 18

• water
• collagen
• PGs
  > ^ collage ^ cartilage stiffness (tensile modulus)
  > In OA disruption to collagen fibres decreases the strength of the solid matrix

Question 19

What are the 2 theories of OA formation?

Answer 19

> wear and tear
- poor capacity of cartilage to repair itself
- no vasculature
biological process
- inblanace between anabolic (decreased) and catabolic (increased|) capabilities of cartilage cells - chondrocytes

Question 20

What site is most common for dog OCD lesions?

Answer 20

Medial trochlear ridge

Question 21

What drives OA formation?

Answer 21

Not classical inflam (few neutrophils, abscnece of systemic inflam)

• but activated B and T cells are ^, providing a source of IL-1b and TNF a
• 2* synovial involvement?

Question 22

Risk factors for OA?

Answer 22

- age
> cellularity v, calcification ^, proliferation of chondrocytes reduced, maybe thinning of cartilage?
- genetic factors 
- sex
- environment
- mechanimcal trauma

Question 23

Is thinning of cartilage predictive of DJD?

Answer 23

NO (study done, thicker cartilage not related to healthy tarsocrural joints)

Question 24

How is weight distribution of cartilage defined?

Answer 24

Surface area, not thickness
- inverseverly proportional to the congruence of the joint (if it is evenly spread foce, the cartilage can be thinner and less deformation is required; if the joint is incongruent the thicker cartilage must be present to allow more deformation and ^ surface area this way )

Question 25

How does “junk accumulation” affect joints?

Answer 25

• proteolytic mediated processing of PGs -> derease in fixed charge density d/t loss of PGs
• accumulation of junk degraded products
• altered activity of cells d/t junk ‘matrikine’ activity

Question 26

Is OA an inevitable consequence of aging?

Answer 26

NO!!!