Biomechanics Connective Tissue Flashcards

1
Q

What are the four types of tissue?

A

connective tissue
muscle
nerve
epithelium

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2
Q

types of connective tissue

A

periarticular connective tissues
-ligament, tendon, perimuscular fascia, capsule, articular cartilage
bone
-specialized CT

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3
Q

composition of periarticular connective tissue (3 general)

-structure drives…

A
fibrous proteins
ground substance
cells
structure drives function
-different composition, proportions, arrangements
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4
Q

fibrous proteins

-types

A

type I, II collagen

elastin

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5
Q

ground substance

-composition

A

proteoglycans (glycosaminoglycans - GAGs)
water
solutes

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6
Q

cells

-types

A

fibroblasts

chondrocytes

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7
Q

type I collagen

  • characteristics
  • higher proportions in
A
characteristics
-thick, little elongation
-stiff, strong
-binds, supports body articulations
higher proportions in
-ligaments
-fibrous joint capsules
-tendons
-perimuscular fascia
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8
Q

type II collagen

  • characteristics
  • higher proportions in
A
characteristics
-thinner than type I
-lower tensile strength
-provide framework, structure for other tissues
-provide internal strength
higher proportions in
-hyaline cartilage
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9
Q

elastin

  • characteristics
  • higher proportions in
A
characteristics
-small fibrils (but larger than type II collagen)
-resist tension but have 'give'
-elastic properties (return to original shape)
higher proportions in
-hyaline cartilage
-perimuscular fascia
-ligamentum flavum
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10
Q

ground substance

  • saturated with
  • GAG molecule
  • -charge
  • –purpose
  • -hydrophilic or hydrophobic?
  • water
  • -purpose
A
saturated with water
GAG molecules
-repel each other --> increases volume
-hydrophilic --> high water content
water
-allows for diffusion of nutrients
-provides mechanical properties
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11
Q

cells

  • functions
  • two specific types
A
functions
-synthesize ground substance
-tissue maintenance and repair
-constant turnover
-do not influence mechanical properties (sparse)
types
-fibroblasts
-chondrocytes
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12
Q

fibroblasts

-found in…

A

ligaments
tendons
supportive CTs

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13
Q

chondrocytes

-found in…

A

hyaline articular cartilage

fibrocartilage

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14
Q

non-muscular soft tissues

  • types (examples)
  • composition
  • characteristics
A

types
-irregular (joint capsules, perimuscular fascia)
-regular (ligaments, tendons, perimuscular fascia)
composition
-HIGH type I collagen
-LOW elastin
-LOW fibroblasts
characteristics
-poor healing (low vascularity)
-adapts to stress/strain with increased stiffness (increased collagen, fibroblast, and GAG synthesis)

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15
Q

irregular dense connective tissue

  • locations
  • how does it get its name?
  • purpose
A

locations
-joint capsule
-perimuscular fascia
how
-collagen is arranged irregularly in ground substance
purpose
-resists tensile forces from multiple directions

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16
Q

regular dense connective tissue

  • locations
  • how does it get its name?
  • purpose
A
locations
-ligaments
-tendons
-fascia
how
-orderly, parallel (or nearly) arrangement of collagen
purpose
-resists tension along the longitudinal axis
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17
Q

ligaments

-purpose

A

constrain excess movement at bony articulations

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18
Q

tendons

  • purpose
  • elastin content vs. ligament
A

transmit large forces from muscle to bone

more elastin in tendon

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19
Q

fascia

-purpose

A

transmits forces between muscles

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20
Q

scar tissue

  • how are collagen fibers laid down?
  • what type of collagen fibers
  • what happens to these fibers?
A

disorganized deposition of collagen fibers
Type II collagen fibers
-remodeled into Type I during maturation phase of healing

21
Q

stress-strain curves

  • stress =
  • strain =
A

stress = force/area (omega)
-newtons/meter squared (Pascal)
strain = change in length/initial length (epsilon)
-measures as percentage

22
Q

stress-strain curves

  • how is stiffness measured
  • how is energy measured?
  • how is elasticity measured
A
stiffness
-slope of linear (elastic) region
energy
-area under curve
elasticity
-Young's Modulus of Elasticity
-stress/strain
23
Q

viscoelastic

-what does it mean and what is an implication?

A

has fluid properties

elastic properties are largely determined by fluid content

24
Q

biological materials toe region

  • what is it?
  • why does it occur?
A

what

  • non-linear beginning to curve
  • due to collagen fibers - begin to straighten and take up slack
25
Q

rate dependent response of biological materials

  • explain
  • faster loading rate results in
A

if you load a tissue rapidly, it behaves differently than if you load it slowly
if loaded rapidly
-increase tissue stiffness (steeper slope in the stress-strain diagram)
-higher modulus

26
Q

viscoelastic creep

  • what is it?
  • when does it happen
  • what characterizes this phenomenon?
A

what
-deformation (strain) response
occurs when exposed to a constant load (stress) for a period of time
characterized by rapid initial deformation, followed by a slow deformation (creep) until equilibrium reached

27
Q

clinical application of creep

A

plastic changes to connective tissue are thought to be brought about by slow, low-intensity, and long-duration stretches

28
Q

what happens if we apply a fast stretch

A

minimal changes due to
1. rate-dependent response to stretch
AND
2. lack of stretch time

29
Q

stress-relaxation

  • what is it
  • when does it occur?
  • purpose
A

stress response
-rapid high initial stress
-followed by a slow decreasing stress required to maintain the deformation
occurs when exposed to a constant deformation
purpose
-distributes the stress across the tissue - protective

30
Q

articular cartilage functions (3)

A

increase area of load distribution for joints
-attenuate joint contact stresses
provide a smooth, wear resistant bearing surface
-near frictionless behavior between joint survaces (due to synovial fluid)
limited capacity for repair
-injuries near sub-chandral bone may heal better
–if it does heal, it repairs with fibrocartilage rather than hyaline cartilage

31
Q

biomechanical behavior

  • contact forces between joint surfaces
  • contact areas between joint surfaces
  • stress =
A
contact forces
-varies greatly depending on the joint and the activity
contact areas
-varies depending on the joint
stress = force/unit area
contact stress can be very high
32
Q

anisotropic material

  • what does it mean
  • what gives it this characteristic
A

mechanical properties very between directions/modes of loading
collagen fiber arrangements and densities vary throughout the tissue

33
Q

bi-phasic material

-composed of…

A
solid components (porous, permeable)
fluid components (incompressible)
34
Q

solid components of articular cartilage

  • what makes up these?
  • organic matrix characteristics
A

organic matrix
-fibrous proteins (type II collagen)
-proteoglycans (PGs): organic part of ground substance
-organic part is strong in tension but not compression (like pulling vs. pushing a string
cells
-chondrocytes: manufacture and maintain organic component

35
Q

PGs

-purposes

A

provides structural framework (along with collagen)

provides stiffness and strength (collagen)

36
Q

fluid components of articular cartilage

  • purpose
  • location
  • permits exchange of _____ between _____ and _____
A

dictates the biomechanical behavior
-viscoelastic responses, resists compression
concentrated near articular surface (80%)
-decreases linearly with depth (65%)
permits exchange between chondrocytes and synovial fluid of
-gases
-nutrients
-waste products

37
Q

water

  • primarily located where?
  • fluid shifts with…
A

most fluid in extracellular matrix
-water, solutes (60-85% of volume)
fluid shifts with
-electrochemical stimuli
–solutes have charges: Na+, K+, Ca2+
-mechanical loads (compression) create pressure gradients
–compression –> deformation –> internal pressure > external pressure –> fluid flows out
–like a saturated spongs
-up to 70% of fluid may shift with compression

38
Q

creep in articular cartilage
-____ is balanced by ____
-creep caused by
-

A

applied load balanced by resistive stress within the tissue
creep caused by fluid ‘leaking’ out (exudation)
when resistive stress in the solid matrix = applied stress
-fluid flow ceases
-creep equilibrium (no further deformation)

39
Q

creep equilibrium

  • how long does it take to reach?
  • how much fluid can be lost
  • condition necessary for recovery
A

takes 4-16 hours to reach creep equilibrium for thick (2-4 mm) articular tissues
50% of the fluid may be lost
recovery if experiment done in physiological conditions

40
Q

stress-relaxation in articular cartilage

  • how is this applied in tissues?
  • what do we find?
A

apply load until equilibrium displacement reached
maintain this displacement, and monitor the stress required
stress-relaxation
-the magnitude of stress required to maintain the equilibrium displacement decreases over time

41
Q

stress-relaxation in articular cartilage

  • initial increase in stress is due to…
  • stress-relaxation is due to
  • purpose during physiological loading
A

initial increase in stress (during displacement phase) due to fluid exudation
stress-relaxation during the displacement maintenance phase due to fluid redistribution
under physiological loading, stress-relaxation attenuates stress developed within the tissue

42
Q

tensile properties of articular cartilage

  • stiffens with…
  • toe region caused by…
  • final elastic region caused by…
  • failure occurs when…
A

stiffens with increasing strain when strain becomes large (ie elastic region)
toe region
-caused by collagen fiber pull-out
final elastic region
-stretching of the straightened collagen fibers
failure
-all fibers rupture

43
Q

cyclic loading (fatigue)

  • occurs in what structures?
  • due to…
A

occurs in cartilage
due to…
-repeated application of high loads over a short time
-repeated application of low loads over a long time

44
Q

proposed mechanisms wearing out (3)

A

tensile failure of collagen fiber network
-accumulate tissue damage leads to lower strength
‘washout’ of PGs from extracellular matrix from repeated fluid exudation/imbibition
-results in decreased stiffness and increased permeability
rapid applications of high loads
-if loads applied too quickly, no time for stress-relaxation (fluid redistribution) resulting in high stresses that may cause damage

45
Q

cartilage defects

A
fibrillation
-splitting of the cartilage surface
-can extend through the full depth to sub-chondral bone
erosion of the cartilage surface
-smooth-surfaced destructive thinning
46
Q

markers of articular cartilage degeneration and how does it occur?

A

progressive deterioration of the tensile properties of solid matrix
loosening of structural collagen matrix responsible for swelling
how
-increase water content: decreased compressive stiffness and increased permeability
-may be influenced by contact stress

47
Q

osteoarthritis

-factors

A

tissue level
-changes in collagen and PG content and structure
loosening of structure
-increased permeability and fluid content
increased fluid flow
-increased deformation –> decreased ability to resist loading
biomechanical changes at muscle/skeletal level may change loading profiles

48
Q

effects of aging (4)

-what can be done?

A

cell turnover (fibroblast and chondrocyte) is decreased
accumulation of microtrauma can lead to tissue failure
smaller and fewer GAG molecules –> lower water content, less force attenuation
decreased tendon stiffness
-collagen fibers become stiffer, but there are fewer of them
mitigated through physical activity