Ligaments and Tendons

Question 1

What are the functions of ligaments

Answer 1

Attach bone to bone

Augment mechanical stability

Guide joint motion

Prevent excessive motion

Question 2

What are the functions of tendons

Answer 2

Connect muscle to bone

Transmit tensile muscle to bone

Aid joint stability

Question 3

What is the role of tendons connecting muscles to bone

Answer 3

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

Question 4

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

Answer 4

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

Question 5

What is the general composition of tendons and ligaments

Answer 5

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

Question 6

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

Answer 6

Enables the tissue to sustain high tensile strengths

Question 7

What is the role of fibroblasts in tendons and ligaments

Answer 7

20% of the tissue volume

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

Question 8

What is contained in the ECM in tendons and ligaments

Answer 8

70% of tissue wet weight is water

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

Has hierarchical structure

Question 9

What is the significance of sparsely vascularised

Answer 9

Generally a poor capacity for healing

Question 10

What is the major component of the tendon and ligament fibres

Answer 10

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.

Question 11

What % of tendons and ligaments are proteoglycan

What is its role

Answer 11

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

Question 12

What occurs in step 1 of hierarchical structure formation

Answer 12

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

Question 13

What is procollagen

Answer 13

Precursor to collagen

Question 14

What is step 2 of the hierarchical structure formation

Answer 14

Collagen molecules are synthesised inside the cell

Secreted into the extracellular space

Self assembly of collagen fibrils (outside the cell)

Question 15

What is fibrillogenesis

Answer 15

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

Question 16

What are fascicles surrounded by

Answer 16

Endotenon (sheets of connective tissue)

Question 17

What is tendon surrounded by

Answer 17

Epitenon (sheets of connective tissue)

Question 18

What is the role of elastin in tendons and ligaments

Answer 18

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)

Question 19

What is the role of ligamentum flavum

Answer 19

Between laminae of vertebrae

Protects spinal nerve roots

Provides intrinsic stability to spine

Question 20

Define enthesis

Answer 20

Place of insertion of a tendon or ligament into bone

Question 21

What can insertion be classified as

Answer 21

Fibrous
Fibrocartilaginous

Classification dependent on the cellular processes involved in their formation

Question 22

What is enthesis innervated with

Answer 22

Proprioceptive and pain receptors

Question 23

What is fibrous insertion formed through

Answer 23

Intramembranous ossification

Distal

Question 24

What is fibrocartilage insertion formed through

Answer 24

Endochondral ossification

Proximal

Question 25

What type of material are tendons, ligaments and entheses

Answer 25

Viscoelastic materials

Question 26

Define load bearing

Answer 26

Transmitting forces from muscles or bone to skeleton

Question 27

What happens when tendons are ligaments weight bear

Answer 27

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

Question 28

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

Answer 28

Maturation and ageing - up to 20 years of age Ageing Pregnancy and postpartum Mechanical demands - Physical training - Immobilisation

Question 29

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

Answer 29

Number and quality of cross-links in collagen molecules increases = increased tensile strength Collagen fibril diameter increased = decreased tensile strength

Question 30

How does ageing affect the mechanical properties of ligaments and tendons

Answer 30

Collagen content of tendon and ligaments decrease = decreased tensile strength

Question 31

How does pregnancy and postpartum affect mechanical properties ligaments and tendons

Answer 31

Tensile strength and stiffness in tendons decreases due to hormonal influences

Question 32

How does physical training affect mechanical properties of ligaments and tendons

Answer 32

Increase tendon tensile strength and ligament - bone interface strength Ligaments become stronger and stiffer, collagen fibres increase in diameter

Question 33

How does immobilisation affect the mechanical properties of ligaments and tendons

Answer 33

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

Question 34

What is the exception from the rule of ligaments and tendons

Answer 34

Patella tendon is a ligament

Question 35

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

Answer 35

Tropocollagen Microfibril Subfibril Fibril Fascicle Endotenon Paratenon or epitenon Tendon Collagen between layers

Question 36

What is the composition of the helix for collagen

Answer 36

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

Question 37

What forms microfibril

Answer 37

5 collagen molecules stacked together

Question 38

Describe a ligament

Answer 38

Connect bone to bone Lower collagen I (90% dry weight) High elastic content Fibre organisation more random Blood supply from insertion points

Question 39

Describe a tendon

Answer 39

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

Question 40

Golgi tendon organ

Answer 40

Encapsulated sensory receptors proprioceptors activated by stretch or active muscle contraction Located in tendons near junction with the muscle (also in joint capsule)

Question 41

Describe the inverse myotatic reflex-protective reflex

Answer 41

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)