Ligaments and Tendons Flashcards
What are the functions of ligaments
Attach bone to bone
Augment mechanical stability
Guide joint motion
Prevent excessive motion
What are the functions of tendons
Connect muscle to bone
Transmit tensile muscle to bone
Aid joint stability
What is the role of tendons connecting muscles to bone
Provides a solid base (insertion to bone) on which muscles can pull
What is the role of tendons transmitting tensile loads from muscle to bone
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
What is the general composition of tendons and ligaments
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
What is the role of dense connective tissue in tendons and ligaments
Enables the tissue to sustain high tensile strengths
What is the role of fibroblasts in tendons and ligaments
20% of the tissue volume
Relatively low cell number leads to a low tissue turnover rate and generally poor capacity for healing
What is contained in the ECM in tendons and ligaments
70% of tissue wet weight is water
30% of solids (collagen, ground substance (proteoglycans and glycoproteins))
Has hierarchical structure
What is the significance of sparsely vascularised
Generally a poor capacity for healing
What is the major component of the tendon and ligament fibres
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.
What % of tendons and ligaments are proteoglycan
What is its role
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
What occurs in step 1 of hierarchical structure formation
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
What is procollagen
Precursor to collagen
What is step 2 of the hierarchical structure formation
Collagen molecules are synthesised inside the cell
Secreted into the extracellular space
Self assembly of collagen fibrils (outside the cell)
What is fibrillogenesis
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
What are fascicles surrounded by
Endotenon (sheets of connective tissue)
What is tendon surrounded by
Epitenon (sheets of connective tissue)
What is the role of elastin in tendons and ligaments
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)
What is the role of ligamentum flavum
Between laminae of vertebrae
Protects spinal nerve roots
Provides intrinsic stability to spine
Define enthesis
Place of insertion of a tendon or ligament into bone
What can insertion be classified as
Fibrous
Fibrocartilaginous
Classification dependent on the cellular processes involved in their formation
What is enthesis innervated with
Proprioceptive and pain receptors
What is fibrous insertion formed through
Intramembranous ossification
Distal
What is fibrocartilage insertion formed through
Endochondral ossification
Proximal
What type of material are tendons, ligaments and entheses
Viscoelastic materials
Define load bearing
Transmitting forces from muscles or bone to skeleton
What happens when tendons are ligaments weight bear
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
What are the factors which affect the mechanical properties of ligaments and tendons
Maturation and ageing - up to 20 years of age
Ageing
Pregnancy and postpartum
Mechanical demands
- Physical training
- Immobilisation
What happens to ligaments and tendons up to 20 years of age
Number and quality of cross-links in collagen molecules increases = increased tensile strength
Collagen fibril diameter increased = decreased tensile strength
How does ageing affect the mechanical properties of ligaments and tendons
Collagen content of tendon and ligaments decrease = decreased tensile strength
How does pregnancy and postpartum affect mechanical properties ligaments and tendons
Tensile strength and stiffness in tendons decreases due to hormonal influences
How does physical training affect mechanical properties of ligaments and tendons
Increase tendon tensile strength and ligament - bone interface strength
Ligaments become stronger and stiffer, collagen fibres increase in diameter
How does immobilisation affect the mechanical properties of ligaments and tendons
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
What is the exception from the rule of ligaments and tendons
Patella tendon is a ligament
What is the structure of tendons and ligaments (from the smallest subunit)
Tropocollagen
Microfibril
Subfibril
Fibril
Fascicle
Endotenon
Paratenon or epitenon
Tendon
Collagen between layers
What is the composition of the helix for collagen
Proline
Hydroxylproline
Approx. every 3rd amino acid is glycine (allows movement)
What forms microfibril
5 collagen molecules stacked together
Describe a ligament
Connect bone to bone
Lower collagen I (90% dry weight)
High elastic content
Fibre organisation more random
Blood supply from insertion points
Describe a tendon
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
Golgi tendon organ
Encapsulated sensory receptors proprioceptors activated by stretch or active muscle contraction
Located in tendons near junction with the muscle (also in joint capsule)
Describe the inverse myotatic reflex-protective reflex
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)
