Articular Cartilage Flashcards
What are the three types of cartilage?
Hyaline (glossy) cartilage (articular cartilage)
Fibrocartilage (ie meniscus)
Elastic cartilage (ears, nose)
What type of cell is found in cartilage?
Chondrocytes - maintains biochemical stasis and structural integrity
Does cartilage contain nerves or blood supply?
No
What is the typical thickness of articular cartilage?
2-4mm
What is the purpose of collagen in articular cartilage?
Resists shear and tensile loading
What is the purpose of proteoglycans and water in articular cartilage?
Resist compressive loading
What type of material is cartilage?
Tri-phasic: organic porous matrix (collagen and proetoglycans) with water and ions
What do proteoglycan aggrecans consist of?
A protein core and glycosaminoglycan chains with chondroitin sulfate and keratin sulfate
What are the charged ions in GAG chains?
COO- and SO3-
Ca2+ and Na+
What are the 4 layers in the macrostructure of cartilage?
- Superficial: high collagen content (circumferential orientation), low proteoglycan
- Middle: Isotropic (random orientation collagen fibres)
- Deep: collagen fibres radially, highest proteoglycan content and lowest water content
- Calcified cartilage: bridge between cartilage and bone
What 2 metabolic activities take place in cartilage?
Anabolic: building and organizing the matrix
Catabolic: degradation and loss of the matrix
What are chondrocytes?
Cells in cartilage which are always under pressure which require mechanical loading to maintain homeostasis
What is the benefit of moderate exercise? What happens at higher magnitudes?
Moderate exercise increases matrix contents and protects the joint, with an increased swelling pressure
Higher levels of exercise can cause chondrocytes to break down the matrix, leading to OA
Why is cartilage a visco-elastic material?
It exhibits elastic and viscous behaviour
Why is cartilage a poroelastic solid?
It’s behaviour is controlled by:
1. Intrinsic, flow independent behaviour of the collagen-proteo matrix (elastic)
2. Flow of interstitial fluid through the matrix and resistance to flow from the matrix (viscous)
What dominates the behaviour of cartilage in vivo?
Fluid flow (viscous)
What resists fluid flow in cartilage?
Intrinsic properties determine matrix properties that do, and the ionic phase also plays a role in restricting fluid flow
How are properties of cartilage determined?
Equilibrium state with no fluid flow
How is the tensile modulus of cartilage affected by water and proteoglycan content
It’s not, the tensile behaviour is a function of the collagen network
Why can dynamic viscoelastic shear testing be used to find shear properties?
There’s no change in volume, therefore no fluid flow
How does increasing the collagen content affect the shear modulus
Increases it
What do dynamic tests of cartilage reveal?
The solid matrix is only slightly viscoelastic, therefore the substantial viscoelastic properties of cartilage are due to fluid flow
How are the compressive properties of cartilage determined?
A uniaxial confined compression creep test or relaxation test
What is the equilibrium compressive modulus referred to as?
The aggregate modulus (Ha), the ratio of applied constant stress to equilibrium strain (typically 0.3-1.3MPa)
