Cartilage

Question 1

What are three types of cartilage (3)

Answer 1

Hyaline (shiny)
Elastic/Yellow (found in ears)
Fibrocartilage (TMJ, Pubic symphysis, menisci)

Question 2

Main constituents of articular cartilage

Answer 2

Water & electrolytes (65-85% wet weight)
Matrix (Collagen II, Aggrecan - a PG)
Chondrocytes

Question 3

Structure of Aggrecan

Answer 3

Aggrecan is a core protein upon which GAG disaccharides bind to
Aggrecan-GAG complex aggregate on a hyaluronate backbone

Question 4

Superficial tangential zone structure

Answer 4

Collagen is tightly packed/dense and parallel to the surface
Fine collagen fibres
Chondrocytes are flattened and dense
Low PG density
Highest water content

Question 5

Superficial tangential zone function

Answer 5

Parallel arrangments of collagen fibres confers:
High shear strength
High tensile strength

Question 6

Middle zone structure

Answer 6

Collagen is randomly organised
Collagen fibres are thicker
Chondrocytes are spherical and low density
Higher PG content
Intermediate water content

Question 7

How do collagen fibres and PGs interact and how does it affect the structure

Answer 7

Collagen forms a scaffold upon which PGs are immobilised
This limits water permeability
PGs attract cations which attract water
This water cannot easily leave –> high compressibility

Question 8

Deep zone

Answer 8

Collagen fibres are perpendicular to articular surface (they cross the tidemark)
Collagen fibres are thickest
Chondrocytes are spherical and arranged in columns perpendicular to articular surface
Highest PG content
Lowest water content

Question 9

Cartilage function (3)

Answer 9

Helps with load bearing - distributes load over larger area
Shock absorber
Provide joints with lubrication

Question 10

Factors affecting mechanical properties: Tension

Answer 10

STZ has densest collagen content, so highest tensile strength
Tensile stiffness and strength depend on collagen content
Upon initial loading there is a toe region where small strains are seen
In the linear region, the collagen fibres re-align the match orientation of the tensile load

Question 11

Factors affecting mechanical properties: Compression

Answer 11

Compression is affected by proteoglycan/GAG content

Speed of compression will determine fluid movement out of cartilage

Question 12

Factors affecting mechanical properties: Shear loading

Answer 12

Directly related to collagen concentration
Shear loading is due to movement of the bone articular surfaces against one another (e.g. rotation)
Does not result in fluid flow
High shear could lead to failure at bone-cartilage boundary

Question 13

Factors affecting mechanical properties: Viscoelasticity

Answer 13

Viscoelastic means cartilage is biphasic
Has elastic/solid (collagen & PG) and viscous/fluid (water) components.
Its stress and strain responses are time-dependent

Question 14

Factors affecting mechanical properties: Time

Answer 14

When loaded quickly in compression, there is no fluid flow due to this low permeability –> increases stiffness
When loaded slowly, there is greater fluid flow

Question 15

Factors affecting mechanical properties: Permeability

Answer 15

Collagen fibres acts as a scaffold upon which PGs are immobilised
This decreases permeability as it is hard for water to flow through
Permeability: STZ > Middle > Deep zone
As cartilage is compressed, water is pushed out and the permeability decreases because negative charge density increases

Question 16

Factors affecting mechanical properties: Hydration

Answer 16

With age and pathological conditions permeability decreases and water content increase
This reduces compressive strength as water leaves more easily

Question 17

Biophysical factors affected by loading (5)

Answer 17

Physiochemical effect
Cell deformation
Increased hydrostatic pressure
Electromechanical effect
Fluid transport

Question 18

Explain Physiochemical effect

Answer 18

Increased Fixed Charge Density in response to compression – PGs are pushed closer together)
Chondrocytes sensitive to extracellular osmolarity, therefore may be able to detect change in osmolarity due to efflux of cations

Question 19

Explain cell deformation

Answer 19

Change in chondrocyte volume stimulates biosynthesis

Loads may induce shear stress on chondrocytes – stimulates aggrecan synthesis

Question 20

Explain Hydrostatic Pressure

Answer 20

Hydrostatic pressures created in the synovial fluid on loading modulates aggrecan biosynthesis via stimulating chondricyte cytokeleton

Question 21

Explain Electromechanical effect

Answer 21

Deformation of the cartilage matrix leads to non-uniform distribution of charge density & electric potentials

Question 22

List causes of Primary Osteoarthritis (1)

Answer 22

Age-related wear and tear

Question 23

List causes of Secondary Osteoarthritis (4)

Answer 23

Post-traumatic injury
Infection (septic arthritis)
Obesity (large loads on joint)
Immbolisation

Question 24

What joints are affected in Osteoarthritis

Answer 24

Weight bearing joints (Knee, Spine, Hip)

Question 25

Genetic Risk factors for OA

Answer 25

Genes involved in endochondral ossification can increase susceptibility

Question 26

Biological risk factors for OA (4)

Answer 26

Obesity
Old age
Gender (female)
High bone density

Question 27

Biomechanical risk factors for OA (2)

Answer 27

Joint malalignment

Joint injury

Question 28

Diagnostic tools for OA

Answer 28

X-ray
MRI
Arthroscopy

Question 29

Treatment/Management of OA (4)

Answer 29

Weight loss
Physiotherapy
Pain management (NSAIDs)
Surgery

Question 30

Surgical treatment of OA (6)

Answer 30

Arthroscopic washout & debridement (early stage only)
Osteotomy
Cartilage graft
Autologous Chondrocyte injection
Microfracture
Knee fusion/Arthodesis (last resort)

Question 31

Explain microfracture

Answer 31

Subchondral bone is fractured/penetrated
Triggers infiltration of Mesencyhmal stem cells which can produce chondrocytes
Usually ends up producing fibrocartilage