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EDKP-206 > Lecture 4 - Tissue Mechanics: Tendons and Ligaments > Flashcards

Lecture 4 - Tissue Mechanics: Tendons and Ligaments Flashcards

1
Q

What do tendons and ligaments have in common?

A
  • Both are composed of dense connective tissue
  • Both are biologically active
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2
Q

What is the difference between tendons vs ligaments?

A
  • Tendons connect muscles to bones
  • Ligaments connect bones to bones
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3
Q

What are the functions of tendons?

A
  • Force transmitter
  • Macroscopic movements (create torque to rotate joint)
  • Alter stress field within bone (compression, bending)
  • Compliance
  • Proprioception
  • Stores elastic energy
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4
Q

What are the functions of ligaments?

A
  • Microscopic movement
  • Force transmission is a minor function
  • Maintains optimal joint alignment
  • Provides joint stability
  • Compliance
  • Proprioception
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5
Q

What are ligaments and tendons classified as?

A

Connective tissue

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6
Q

What are the three categories of connective tissue?

A
  1. Proper connective tissue:
    a) Loose: within and between
    muscle sheaths, delicate
    b) Dense: less flexible,
    resistant to stress (tendons
    and ligaments)
  2. Supporting connective tissue:
    a) Bone
    b) Cartilage
  3. Specialized connective tissues:
    a) Adipose tissue
    b) Hematopoietic tissue
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7
Q

What are the components of tendons and ligaments?

A
  • Cells: 20%
  • Extracellular Matrix (ECM): 80%
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8
Q

What makes up the ECM?

A

a) Fibers
- Collagen
- Elastic
b) Ground substance
- Glycoproteins
- Protoglycans
- Inorganic components
- H20

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9
Q

What is the primary type of cell?

A

Fibrocyte/tenocytes

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10
Q

What are fibroblasts?

A

What fibrocytes are called when manufacturing proteins

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11
Q

What do fibroblasts manufacture?

A

Components of the ECM

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12
Q

What primarily makes up the ECM?

A

Collagen (gives white colour and provides tensile strength)

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13
Q

What do fibroblasts secrete?

A

Procollagen

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14
Q

What does procollagen assemble into?

A

Tropocollagen

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15
Q

What does tropocollagen assemble into?

A

Tendons and ligaments

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16
Q

What is the composition of tendons high in?

A

Collagen (75-85%)
greater than ligaments

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17
Q

What is the composition of ligaments high in?

A
  • Collagen (70-80%)
  • Elastin (5-15%)*
    greater than tendons
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18
Q

What are the arrangements of collagen fibers in tendons and ligaments?

A

Tendons: Parallel
Ligaments: Less parallel

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19
Q

In composition, what are tendons and ligaments similar in?

A
  • Water (~55-65%)
  • Dry matter (30-45%)
20
Q

What does the parallel arrangement of collagen fibers help with?

A

Withstanding high unidirectional loads

21
Q

What does the less parallel arrangement of collagen fibers help with?

A

Sustain tensile stresses in one direction and smaller stresses in other

22
Q

What are the two ways to measure tissue properties?

A
  1. Subjecting tissue preparations to uniaxial tensile loads to failure
  2. Measurement of in vivo forces
23
Q

What are load deformation curves?

A
  • Represents structural properties of the tissue
  • Deformation produced by a load depends on the size of the structure
24
Q

What is tensile stress?

A

Externally applied tensile load per cross sectional area

25
Q

What is tensile strain?

A

the elongation/unit length of material in response to tensile load

26
Q

What do mechanical properties depend on?

A
  1. Composition of the tissue
  2. Orientation of collagen fibers
  3. Number/type of collagen cross links
  4. Components of ground substance
27
Q

What do the slopes of the stress-strain curves indicate?

A

Steep slope: high Young’s modulus (stiffness)
Gradual slope: low Young’s modulus (compliant)

28
Q

What are the different parts of a stress-strain curve?

A
  1. Toe:
    - Elongation
    - Uncrimpling of collagen
  2. Linear:
    - Slippage b/w fibers
    - Return to initial length
  3. Plastic:
    - Microfailures
    - Collagen structure disrupted
  4. Major failure
    - Visible narrowing
  5. Complete failure
29
Q

What are some findings of comparing stress-strain curves?

A
  • Differences between connective tissue types
  • Cortical bone requires major stress
  • Cartilage and trabecular bone deform easily
30
Q

What are the characteristics of viscoelasticity?

A
  1. Creep
  2. Stress relaxation
  3. Recovery
  4. Rate effects
31
Q

What tissues are viscoelastic?

A

Tendons and ligaments

32
Q

What is viscoelasticity?

A

Time-dependent response of a material subjected to a constant load or deformation

33
Q

What is hysteresis?

A

The amount of energy lost during loading

34
Q

What makes up a hysteresis graph?

A
  • The loading curve of a viscoelastic material
  • The unloading curve of a viscoelastic material
35
Q

What are the 3 modes of failure?

A
  1. Rupture (tearing)
  2. Failure through the enthesis (attch. point near bone)
  3. Avulsion failure (pulling away of bony attachment)
36
Q

What affects the failure modes?

A
  • Varies among different tendons/ligaments
  • Affected by age, speed, structure, etc
37
Q

What are the effects of rate and duration of force application?

A
  1. Tendons are more sensitive to strain rate
  2. Higher strain rates increase stiffness
  3. Strain rates may affect the mode of failure
    - Avulsion: lower strain rate
    - Substance rupture: higher strain rate
  4. Tendons and ligaments are viscoelastic
    - Rapid loads: stiffer and abrupt rupture
    - Slow loads: fluid and elongate
38
Q

What are the effects of temperature?

A
  • Heat (>55-60 degrees): produce irreversible shrinkage
  • Viscoelastic properties increase with increased temperature: increased stress relaxation/creep
39
Q

What are the effects of maturation and aging?

A
  • Maximal tissue strength achieved at skeletal maturity
  • Very young/old: lower stress/strain and decreased stiffness
  • Resistance training can reverse or slow effects of aging
40
Q

What are the effects of hormones?

A
  • Cortisol and glucocorticoids: reduce the synthesis of type I collagen
  • Relaxin: softens and increases extensibility
  • Growth hormone: increases collagen synthesis
41
Q

What is tissue remodelling?

A

Adaptation of biological tissues to change in the mechanical stresses they are subjected to daily

42
Q

What is specific adaptation to imposed demand?

A

Explains remodelling in response to alterations in external loading in soft tissues

43
Q

What effects does joint immobilization have in normal connective tissue?

A
  • Reduces the tensile forces
  • Reduces the load to failure and stiffness
  • Decreases the strain/elongation to failure
  • Frequency of avulsion failures increases
44
Q

What effects does joint remobilization have in normal connective tissue?

A
  • Allows restoration of mechanical properties
45
Q

What happens to healing connective tissue?

A
  • Healing is slow
  • Early mobilization (within limits) strengthens the unions, speeds healing and reduces scar tissue adhesions
46
Q

What are the 4 stages of healing?

A
  1. Hemorrhagic
  2. Inflammatory
  3. Proliferative
  4. Remodelling and maturation
47
Q

What is the response to stress enhancement?

A
  • Increased loading can lead to tendon hypertrophy and increased strength/stiffness
  • Exercise may protect against weakening effects of inactivity
  • Exercise may increase the strength of some tissues
  • Excessive loads can have harmful effects

EDKP-206 (16 decks)

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