9: Soft Tissue Mechanics III - Vardaxis

Question 1

most predominant cartilage in body

Answer 1

articular/hyaline

found in diarthrodial joints and growth plates

Question 2

cartilage found in intervertebral disks, mandibular condyles, and meniscus

Answer 2

fibrocartilage

Question 3

cartilage found in epiglottis, eustachian tube

Answer 3

elastic cartilage

Question 4

cartilage reading % composition #s

Answer 4

water - 65-85% ww
collagen - 75% dw
proteoglycan - 20-25% dw

Question 5

which part of the intervertebral disc has more collagen?

Answer 5

annulus fibrosus (50-70% collagen dw; 10-20% proteoglycan dw)

nucleus pulpsus (15-25% collagen dw; 50% proteoglycan dw)

Question 6

functions of hyaline cartilage

Answer 6

• supports/transmits loads across mobile surfaces
• distributes joint loads over a wider area (stress reduction)
• stabilize and guide joint motion
• lines the ends of bones (prevents wear)
• lubrication reduces friction coefficient

Question 7

is hyaline cartilage a shock absorber?

Answer 7

NO

-very thin, capacity is negligible compared to muscles and bones

Question 8

produce collagen and proteoglycans as needed; release enzymes to breakdown aging components

Answer 8

chondrocytes ( 1% dw)

Question 9

collagen orientation

Answer 9

• parallel to the surface on the superficial layer
• oblique in the middle layer
• perpendicular to the surface in the deep zonr

Question 10

why is attraction of water highest toward the middle of cartilage?

Answer 10

proteoglycan content increases from surface til lthe middle zone and diminishes toward the deep zone

Question 11

describe the different zones of hyaline cartilage

Answer 11

superficial zone: densely packed collagen fibrils, organized parallel to articular surface, oblong chondrocytes
middle zone - fibers more or less randomly arranged, greater fiber diameter, round chondrocytes

deep zone: cells arranged in columns along the radial direction

Question 12

where do large fibers from the deep zone anchor?

Answer 12

calcified cartilage and subchondral bone

Question 13

____ of water in cartilage is bound to proteoglycans

Answer 13

70%

remaining 30% bound to collagen

Question 14

what is the significance of the inorganic ions dissolved in water binding in cartilage?

Answer 14

balances fixed charges on proteoglycans and generate swelling pressure

Question 15

creates a framework that houses the other components of cartilage

Answer 15

collagen

Question 16

what type of collagen is in cartilage?

Answer 16

type II

Question 17

collagen provides cartilage with its _____ strenght

Answer 17

tensile

Question 18

characteristics of tissues with high proteoglycan content

Answer 18

• high water content
• low hydraulic permeability
• high compressive stress

Question 19

damage to proteoglycans will result in …

Answer 19

increased water mobility and impaired mechanical function

Question 20

describe the pathway of how resistance to compression is achieved?

Answer 20

external load –> deformation –> internal pressure increase –> liquid flows out of tissue –> PG concentration increases –> osmotic swelling pressure increases –> resistance to compression is achieved!

Question 21

does cartilage behave the same across the joint?

Answer 21

no - anisotropic due to inhomogenous distribution of collagen and PGs

Question 22

describe the stress-strain graph of cartilage

Answer 22

toe region: collagen fibrils straighten out and un-crimp
linear region: parallels the tensile strength of collagen fibrils, collagen aligns with axis of tension
- no plastic region
- failure region

Question 23

tensile loading is generated by ..

Answer 23

intrinsic stiffness of collagen fibers

Question 24

tensile modulus =

Answer 24

• stiffness
• it is a measure of resistance to tensile loading and depends on density of collagen fibers, orientation of collagen fibers, type or amount of collagen cross linking

Question 25

tensile modulus varies 5-25 MPa depending on …

Answer 25

• location of joint surface (high or low weight bearing region)
• depth of specimen
• orientation of specimen relative to joint surface

Question 26

permeability decreases in an exponential manner as a function of ..

Answer 26

both increasing applied compressive strains and increasing applied pressure

Question 27

the decrease of permeability with compression acts to …

Answer 27

retard rapid loss of interstitial fluid during high joint loadings

Question 28

mechanism of protection of the cartialge solid matrix from stresses and strains associated with normal joint loading

Answer 28

low permeabilit of the matrix t ofluid flow creates energy dissipation through high fluid pressure, very high drag forces between fluid and solid matrix

Question 29

what is the cartilage response to shear force?

Answer 29

• stretching and deformation of the solid matrix

- this deformation is without a change in volume, no pressure gradient, no fluid flow through the matrix

Question 30

at equilibrium, cartilage is ina state of …

Answer 30

pre-stress

Question 31

less than ___ weight change in health human cartialge

Answer 31

3%

• 30% in the degenerate cartilage
• swelling effects are recorded by means of tissue weight change

Question 32

for a 2-4 mm human or bovine articular cartilage it takes _________ to reach creep equilibrium

Answer 32

4-16 hr

Question 33

what allows for stress-relaxation phase in cartilage?

Answer 33

fluid redistribution

Question 34

describe OA

Answer 34

• normal balance of anabolism and catabolism of extracellular matrix gets disrupted
• tensile and compressive moduli of cartilage decrease with OA severity (tsnile and comprssive stiffness decreases - due to disorganized extracellular matrix)
• hydraulic permeability increases