Cartilage Flashcards
The nose and ear are made up of what kind of cartilage?
Elastic cartilage
What structures are composed of fibrocartilage?
1 - iliac surface of SI joint
2 - menisci of the knee
3 - annular fibers of the disc
Function of joint cartilage (2)
1 - decrease contact stress by spreading load over a larger area
2 - allow movement of articular surfaces with minimal wear and friction
Can hyaline cartilage heal quickly? Why or why not?
No, because there is no nerve supply, no blood supply, no lymph supply.
What are the components of cartilage?
Solid matrix
Chondrocytes
Water
The solid matrix of cartilage is composed of what?
60% collagen and 40% proteoglycan gel
Percentages are by weight
Function of collagen (2)
1 - provides ultrastructure for cartilage
2 - provides tensile stiffness and strength
Note: cartilage undergoes compression; collagen resists tensile load — collagen helps cartilage do its job by resisting tensile load
Why is collagen better suited (compared to cartilage) in resisting tensile loads rather than compressive?
?
Loading of tensile force makes the fibers straighten.
How is collagen arranged in zone 1?
Superficial zone: thickest zone. Random packed, random orientation in planes parallel to the surface
How is collagen arranged in zone 2?
Middle zone — least amount of thickness. Random orientation and loosely packed.
How is collagen arranged in zone 3?
Deep zone — medium amount of thickness. Perpendicular ordination, anchor to bone and fibrocartilage.
The proteoglycan gel is composed of (2)
1 - Protein core
2 - Aggrecans
What are aggrecans composed of and how do they help establish sponge model?
Aggrecans are negatively charged so they repulse/resist each other. This makes an inherent stiffness. It’s the anions that stiffens the Proteoglycan Gel and resists compression.
How does water move to protect joints?
1 - proteoglycan gel attracts cations and sets up osmotic pressure
2 - cations osmotically draw water molecules into cartilage
So the cartilage stiffens and swells due to A) the repulsive force of aggrecans and B) the osmotic pressure attracting water
Under stress:
A- water squeezed out
B- produces increased swelling pressure (osmotic pressure)
C- equilibrium is re-established when swelling pressures balances the stress
What zone is most of the water located in the cartilage? and why is this important?
Superficial zone (zone 1).
That means 70% of the water is free to move
Most of the creep in cartilage is due to what?
Exudation of fluid
What is the speed of creep as it applies to cartilage? Under a constant load…
Viscoelastic material deforms quickly at first and then more slowly over time until equilibrium is met
What is the syringe effect?
With a slow load, more fluid comes out
With a fast load, there is resistance of fluid movement.
How does cartilage behave in high speed loading?
Little deformation.
Because, syringe effect: not enough time to squeeze water out of tissue, therefore cartilage is very stiff.
E.g. discs = good shock absorbers
How fast is the restoration when you unload after a slow load?
1 - Immediate restoration to 90% via elastic recoil
2 - Slower restoration via swelling pressure
E.g. being on your feet all day: take a seat and you’ll restore 90% thickness nearly immediately
What kind of fluid acts as lubricant between articular surfaces?
Synovial fluid
Name 2 types of lubrication
Fluid film
Boundary
What is fluid film lubrication?
Thick film of lubricant that separates surfaces and occurs in physiologic loading
Types of fluid film lubrication (2)
Hydrodynamic
Squeeze film
What kind of fluid film lubrication creates a lifting action that keeps surfaces apart and reduces friction?
Hydrodynamic lubrication
What kind of fluid film lubrication happens on non-parallel surfaces and with tangential movement?
Hydrodynamic lubrication
What kind of fluid film lubrication is sufficient for high loads for short durations?
Squeeze lubrication
What kind of fluid film lubrication are perpendicular force? And the viscosity holds the lubricant together so that it doesn’t escape from between the surfaces.
Squeeze lubrication
What kind of lubrication is good in “severe loading” and is when monolayer of synovial fluid absorbs to surfaces?
Boundary lubrication
The unwanted removal of material from solid surfaces by mechanical action
Cartilaginous wear
2 types: interfacial wear and fatigue wear
What kind of cartilage wear happens from interaction of articular surfaces and is unlikely in healthy cartilage because of effective lubrication?
Interfacial wear
What are 5 qualities of Interfacial wear?
By adhesion and abrasion Wear produces surfaces defects Softening and increased permeability Fluid leakage Loss of lubrication (into defects in the surface)
What kind of cartilage wear occurs with repetitive cyclic loading (and the reloading occurs before cartilage has time to fully re-imbibe)?
Fatigue wear
What type of cartilage wear involves repetitive stress on matrix, collagen fiber disruption, proteoglycan macromolecule disruption and microstructural disruption that leads to degeneration?
Fatigue wear
Note: repetitive exudation and imbibition may “wash out” degraded proteoglycan gels
What occupations lead to cartilage injury because of high repetitive loads?
Football player’s knees and ballet dancer’s ankles (high repetitive loads)
Loss of muscle balance can led to cartilage injury because:
Loss of flexibility prevents loads from being evenly distributed through joint surface
“Pebble in a shoe” defect focuses load into one area and can lead to cartilage injury. How might this happen (4)?
Intra-articular fracture
Meniscectomy
Slipped femoral epiphysis
Ligamentous instability
Disease that can lead to cartilage injury though matrix destruction include:
RA
Joint space hemorrhage
Collagen disorders
Immobility can lead to cartilage injury because of
Decreased synovial fluid circulation
Rapid high impact loads may not allow fluid to redistribute rapidly enough, causing high internal fluid pressure at the PG-collagen matrix (what kind of cartilage wear is this?)
Fatigue wear
