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MSK > Ligaments and Tendons > Flashcards

Ligaments and Tendons Flashcards

1
Q

What are the functions of ligaments

A

Attach bone to bone

Augment mechanical stability

Guide joint motion

Prevent excessive motion

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2
Q

What are the functions of tendons

A

Connect muscle to bone

Transmit tensile muscle to bone

Aid joint stability

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3
Q

What is the role of tendons connecting muscles to bone

A

Provides a solid base (insertion to bone) on which muscles can pull

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4
Q

What is the role of tendons transmitting tensile loads from muscle to bone

A

Produce joint torque

Stabilise joint during isometric contractions and in opposition to other torques

Enable joint motion during isotonic contractions

Acts as a dynamic joint restraint

Interact with ligaments and joint capsule to mitigate loads that they receive

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5
Q

What is the general composition of tendons and ligaments

A

Dense connective consisting of mainly parallel fibres

Cells (fibroblasts also called tenocytes) which synthesise and remodel the ECM

Extracellular matrix (ECM) - 80% of the tissue volume

Sparsely vascularised

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6
Q

What is the role of dense connective tissue in tendons and ligaments

A

Enables the tissue to sustain high tensile strengths

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7
Q

What is the role of fibroblasts in tendons and ligaments

A

20% of the tissue volume

Relatively low cell number leads to a low tissue turnover rate and generally poor capacity for healing

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8
Q

What is contained in the ECM in tendons and ligaments

A

70% of tissue wet weight is water

30% of solids (collagen, ground substance (proteoglycans and glycoproteins))

Has hierarchical structure

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9
Q

What is the significance of sparsely vascularised

A

Generally a poor capacity for healing

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10
Q

What is the major component of the tendon and ligament fibres

A

Collagen
90-95% of dry weight = type 1
Some type 3
Small amounts of other collagen - 5, 6, 9 which function to control fibril diameter.

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11
Q

What % of tendons and ligaments are proteoglycan

What is its role

A

1-5%

Regulate fibre diameter during fibrillogenesis (biglycan and decorin) - aid in keeping fibrils together

Acts as lubricant to aid collagen fibres gliding over each other

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12
Q

What occurs in step 1 of hierarchical structure formation

A

Collagen molecules are synthesised within fibroblast as procollagen

Consists of 3 individual polypeptide chains (a chains) each coiled in left hand helix

3 a chains combine in right handed triple helix

Bonding (cross-linking) between a chains enhances strength of collagen molecules

Secreted outside the cell, processed to remove terminal peptides (for tropocollagen) and self assembles into collagen fibres

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13
Q

What is procollagen

A

Precursor to collagen

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14
Q

What is step 2 of the hierarchical structure formation

A

Collagen molecules are synthesised inside the cell

Secreted into the extracellular space

Self assembly of collagen fibrils (outside the cell)

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15
Q

What is fibrillogenesis

A

Collagen molecules group together to form microfibrils

Microfibrils combine to form subfibrils

Subfibrils combine to form fibrils (50-200nm d)

Fibrils combine together to form fibres (3-7 um d)

Fibres combine to form fascicles

Fascicles group together to form tendon

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16
Q

What are fascicles surrounded by

A

Endotenon (sheets of connective tissue)

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17
Q

What is tendon surrounded by

A

Epitenon (sheets of connective tissue)

18
Q

What is the role of elastin in tendons and ligaments

A

Influences elastic properties of tendons and ligaments

Increased elastin = increased elasticity

Proportion varies by function
- little in tendons and extremity ligaments
- More present in ligamentum flavum (between laminae of vertebrae)

19
Q

What is the role of ligamentum flavum

A

Between laminae of vertebrae

Protects spinal nerve roots

Provides intrinsic stability to spine

20
Q

Define enthesis

A

Place of insertion of a tendon or ligament into bone

21
Q

What can insertion be classified as

A

Fibrous
Fibrocartilaginous

Classification dependent on the cellular processes involved in their formation

22
Q

What is enthesis innervated with

A

Proprioceptive and pain receptors

23
Q

What is fibrous insertion formed through

A

Intramembranous ossification

Distal

24
Q

What is fibrocartilage insertion formed through

A

Endochondral ossification

Proximal

25
Q

What type of material are tendons, ligaments and entheses

A

Viscoelastic materials

26
Q

Define load bearing

A

Transmitting forces from muscles or bone to skeleton

27
Q

What happens when tendons are ligaments weight bear

A

Tensile load results in elongation between the original ends of the tissues

Compressive load results in contraction between the tissue ends

Mechanical cues affect healing, homeostasis

28
Q

What are the factors which affect the mechanical properties of ligaments and tendons

A

Maturation and ageing - up to 20 years of age

Ageing

Pregnancy and postpartum

Mechanical demands
- Physical training
- Immobilisation

29
Q

What happens to ligaments and tendons up to 20 years of age

A

Number and quality of cross-links in collagen molecules increases = increased tensile strength

Collagen fibril diameter increased = decreased tensile strength

30
Q

How does ageing affect the mechanical properties of ligaments and tendons

A

Collagen content of tendon and ligaments decrease = decreased tensile strength

31
Q

How does pregnancy and postpartum affect mechanical properties ligaments and tendons

A

Tensile strength and stiffness in tendons decreases due to hormonal influences

32
Q

How does physical training affect mechanical properties of ligaments and tendons

A

Increase tendon tensile strength and ligament - bone interface strength

Ligaments become stronger and stiffer, collagen fibres increase in diameter

33
Q

How does immobilisation affect the mechanical properties of ligaments and tendons

A

Decrease tensile strength of ligaments, more elongation, less stiff

Decrease in cross-links

After 8 weeks of immobilisation - 12 months to recover strength and stiffness

34
Q

What is the exception from the rule of ligaments and tendons

A

Patella tendon is a ligament

35
Q

What is the structure of tendons and ligaments (from the smallest subunit)

A

Tropocollagen
Microfibril
Subfibril
Fibril
Fascicle
Endotenon
Paratenon or epitenon
Tendon

Collagen between layers

36
Q

What is the composition of the helix for collagen

A

Proline
Hydroxylproline

Approx. every 3rd amino acid is glycine (allows movement)

37
Q

What forms microfibril

A

5 collagen molecules stacked together

38
Q

Describe a ligament

A

Connect bone to bone
Lower collagen I (90% dry weight)
High elastic content
Fibre organisation more random

Blood supply from insertion points

39
Q

Describe a tendon

A

Connect muscle to bone
Higher collagen I (95-99% dry weight)
Very little elastin
Fibres highly organised

Either
Vascular - surrounded by a paratenon
Avascular - surrounded by a tendon sheath

40
Q

Golgi tendon organ

A

Encapsulated sensory receptors proprioceptors activated by stretch or active muscle contraction

Located in tendons near junction with the muscle (also in joint capsule)

41
Q

Describe the inverse myotatic reflex-protective reflex

A

Stimulation of GTO
Nerve impulse travels to spinal cord (afferent 1b neurones)
Synapse on interneuron
Alpha motor neurone innervating muscle
Muscle relaxation

(Prevention of muscle and tendon damage)

MSK (13 decks)

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