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Orthopaedic Biomechanics > Tendons & Ligaments > Flashcards

Tendons & Ligaments Flashcards

1
Q

Function of tendon

A

Connect muscle to bone

Transmit tensile forces from muscle to bone to allow movement

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2
Q

Function of ligaments

A

Connect bone to bone
Stabilises joints so prevents excessive movement
Proprioceptive function

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3
Q

What is the cellular component of tendons & ligaments

A

Fibroblasts (tenocytes in tendons) - synthesise ECM & collagen

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4
Q

What type of collagens are found in tendons and ligaments

A

Type 1 & 3

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5
Q

Difference between structure of tendons & ligaments (4)

A

More collagen in tendons
Less elastin in tendons
Less ground substance in tendons
Tendons have predominantly Type 1 and trace Type 3

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6
Q

Why do tendons have little/negligible elastin

A

They need to transmit tensile forces to bone

Stretching tendons would waste energy

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7
Q

Components of ligaments & tendons

A

Water
Collagen types 1 & 3
Ground substance (matrix of GAG, PGs and other ECM components)
Elastin

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8
Q

How are collagen fibres arranged in tendons and why

A

the large fibres are regularly arranged in PARALLEL

tendons transmit UNIDIRECTIONAL force from muscle

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9
Q

How are collagen fibres arranged in ligaments and why

A

smaller diameter fibres are arranged randomly

ligaments can be loaded in many directions depending on movement

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10
Q

What does the endotenon do?

A

Thin sheet of connective tissue what wraps around fibrils & fascicles
permits some longitudinal movement of the bundles relative to each other
Contains vessels, lymphatics & nerve supply

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11
Q

What does the epitenon do?

A

Wraps around bundles of fascicles
Contains vessels, lymphatics & nerve supply
Produces synovial fluid, reducing friction between itself and paratenon

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12
Q

What does the paratenon do?

A

The outermost layer of tendon
Nerves and blood vessels run through it
Allows tendons to glide freely

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13
Q

What are vascular tendons?

A

Tendons that are surrounded by paratenon
They have rich blood supply
They don’t wrap around structure

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14
Q

What are avascular tendons?

A

Tendons that are surrounded by a synovial sheath
Less vascularised
Receive nutrients via diffusion from synovial fluid
Wrap around joints

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15
Q

describe Direct Insertion into bone

A

Superficial fibres join the periosteum

Deeper fibres transition from tendon/ligament –> fibrocartilage –> mineralised fibrocartilage –> bone

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16
Q

describe Indirect insertion into bone

A

Superficial fibres join the periosteum

Deep fibres insert directly into bone via perforating (mineralised) collagen fibres

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17
Q

How are ligaments supplied with blood

A

Receive nutrition via Micro-vessels at the insertion site

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18
Q

Explain the process of fibre recruitment

A

Fibres across the length have varying stiffnesses
When loaded different fibres experience different strains
As magnitude of applied force increases, stiffer fibres are recruited
This is non-linear elastic behaviour

19
Q

What is the toe region in the force-extension curve

A

An area where significant deformation is seen for small stresses
There is straightening out of crimped collagen fibres and re-orientation in the direction of loading

20
Q

Why is failure unpredictable

A

fibres have different stiffnesses

21
Q

Material vs Structural properties

A

Material properties look at things like Ultimate stress/strain, Young’s modulus and is independent of geometric properties of the object

Structural properties focus on the geometry of the specific object

22
Q

Mechanics of tendons v ligament

A

Tendon have greater ultimate tensile strength and strain

Tendons have greater (linear) Youngs Modulus

23
Q

Why is okay that ligaments are less stiff

A

Their function is the support movement of joints

Too much stiffness would limit motion

24
Q

Compare toe regions of tendons and ligaments

A

Tendons experience larger forces so recruit fibres more quickly –> shorter toe region
Ligaments experience less force so recruits fibres gradually –> longer toe region

25
Q

Mechanics of ligamentum flavae

A

Composed of 60-70% elastic fibres
Able to stretch up to 70% of their original length before failing
It is always pre-stressed to prevent buckling upon extension

26
Q

Mechanical testing methods

A

Place between grips and apply a TENSILE load
Extensometers may be used (2 clips are placed and the change in distance between them is measured)
Optical markers along the tendon can be tracked with a camera and produce digital image

27
Q

Challenges of using grips for mechanical testing

A

Area lost due to grips
Slippage
Extensometer could puncture tendon/ligament

28
Q

Advantage of Optical measurement

A

No slippage
Non-invasive
No damage to specimen

29
Q

Measuring cross-sectional area of tendon

A 
Use calipers (contact)
Laser micrometer (non-contact)
30
Q

Factors affecting biomechanical properties (7)

A 
Orientation of loading - anisotropic
Molecular Components 
Temperature 
Stresses experienced
Shear rate
Viscoelasticity (exhibits creep & stress relaxation)
Water content
31
Q

Factors affecting biomechanical properties: Molecular makeup

A

PG content, Collagen content and type, elastin content

32
Q

Factors affecting biomechanical properties: orientation

A

Higher stiffness and ultimate tensile strength in longitudinal > transverse

33
Q

Factors affecting biomechanical properties: Temperature

A

Increasing temperature increases creep and decreases stiffness

34
Q

Factors affecting biomechanical properties: Level of stress experienced

A

Tendons experience more stress than ligaments
Flexors experience more stress than extensors
Levels of mobilisation

35
Q

Factors affecting biomechanical properties: Shear rate

A

Higher strain rate:
Higher stiffness/modulus and ultimate strength
Failure seen at ligament bone interface (where superficial fibres join periosteum)
Lower strain rate: Failure occurs at deep bony insertion

36
Q

Factors affecting biomechanical properties: Hydration

A

Less water increases stiffness

37
Q

Effect of age on tendon & ligament strength

A

Stiffness increases up until skeletal maturity
In animals they remain at this strength all their life
In humans this strength declines with age

38
Q

effects of Mobilisation

A
  • Increase in strength and stiffness (esp at bone-ligament/tendon junction)
  • Increase in collagen fibre diameter
  • Increase collagen cross-linking
39
Q

effect of immobilisation

A
  • Decrease in modulus/ ultimate stress

* Remobilisation can increase strength again and tendons/ligaments take a lot longer to do so

40
Q

Tendon injuries (5)

A

Tendinosis (chronic inflammation)
Tendinitis (inflammation due to acute injury)
Peritendinitis (inflammation of tendon sheath)
Direct: laceration
Indirect: tendon overload

41
Q

Ligament injuries

A

Sprain/Tear: overstretched ligaments

42
Q

Treatments for injured ligaments/tendons

A

Rest and rehab
Suturing
Allo/Autograft

43
Q

Challenges to repair (3)

A

Relatively avascular
Function is not easily restored due to scar tissue formation
Most injuries occur at muscle-tendon junction or bony insertion

Orthopaedic Biomechanics (15 decks)

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