Tendons & Ligaments Flashcards
Function of tendon
Connect muscle to bone
Transmit tensile forces from muscle to bone to allow movement
Function of ligaments
Connect bone to bone
Stabilises joints so prevents excessive movement
Proprioceptive function
What is the cellular component of tendons & ligaments
Fibroblasts (tenocytes in tendons) - synthesise ECM & collagen
What type of collagens are found in tendons and ligaments
Type 1 & 3
Difference between structure of tendons & ligaments (4)
More collagen in tendons
Less elastin in tendons
Less ground substance in tendons
Tendons have predominantly Type 1 and trace Type 3
Why do tendons have little/negligible elastin
They need to transmit tensile forces to bone
Stretching tendons would waste energy
Components of ligaments & tendons
Water
Collagen types 1 & 3
Ground substance (matrix of GAG, PGs and other ECM components)
Elastin
How are collagen fibres arranged in tendons and why
the large fibres are regularly arranged in PARALLEL
tendons transmit UNIDIRECTIONAL force from muscle
How are collagen fibres arranged in ligaments and why
smaller diameter fibres are arranged randomly
ligaments can be loaded in many directions depending on movement
What does the endotenon do?
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
What does the epitenon do?
Wraps around bundles of fascicles
Contains vessels, lymphatics & nerve supply
Produces synovial fluid, reducing friction between itself and paratenon
What does the paratenon do?
The outermost layer of tendon
Nerves and blood vessels run through it
Allows tendons to glide freely
What are vascular tendons?
Tendons that are surrounded by paratenon
They have rich blood supply
They don’t wrap around structure
What are avascular tendons?
Tendons that are surrounded by a synovial sheath
Less vascularised
Receive nutrients via diffusion from synovial fluid
Wrap around joints
describe Direct Insertion into bone
Superficial fibres join the periosteum
Deeper fibres transition from tendon/ligament –> fibrocartilage –> mineralised fibrocartilage –> bone
describe Indirect insertion into bone
Superficial fibres join the periosteum
Deep fibres insert directly into bone via perforating (mineralised) collagen fibres
How are ligaments supplied with blood
Receive nutrition via Micro-vessels at the insertion site
Explain the process of fibre recruitment
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
What is the toe region in the force-extension curve
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
Why is failure unpredictable
fibres have different stiffnesses
Material vs Structural properties
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
Mechanics of tendons v ligament
Tendon have greater ultimate tensile strength and strain
Tendons have greater (linear) Youngs Modulus
Why is okay that ligaments are less stiff
Their function is the support movement of joints
Too much stiffness would limit motion
Compare toe regions of tendons and ligaments
Tendons experience larger forces so recruit fibres more quickly –> shorter toe region
Ligaments experience less force so recruits fibres gradually –> longer toe region
Mechanics of ligamentum flavae
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
Mechanical testing methods
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
Challenges of using grips for mechanical testing
Area lost due to grips
Slippage
Extensometer could puncture tendon/ligament
Advantage of Optical measurement
No slippage
Non-invasive
No damage to specimen
Measuring cross-sectional area of tendon
Use calipers (contact) Laser micrometer (non-contact)
Factors affecting biomechanical properties (7)
Orientation of loading - anisotropic Molecular Components Temperature Stresses experienced Shear rate Viscoelasticity (exhibits creep & stress relaxation) Water content
Factors affecting biomechanical properties: Molecular makeup
PG content, Collagen content and type, elastin content
Factors affecting biomechanical properties: orientation
Higher stiffness and ultimate tensile strength in longitudinal > transverse
Factors affecting biomechanical properties: Temperature
Increasing temperature increases creep and decreases stiffness
Factors affecting biomechanical properties: Level of stress experienced
Tendons experience more stress than ligaments
Flexors experience more stress than extensors
Levels of mobilisation
Factors affecting biomechanical properties: Shear rate
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
Factors affecting biomechanical properties: Hydration
Less water increases stiffness
Effect of age on tendon & ligament strength
Stiffness increases up until skeletal maturity
In animals they remain at this strength all their life
In humans this strength declines with age
effects of Mobilisation
- Increase in strength and stiffness (esp at bone-ligament/tendon junction)
- Increase in collagen fibre diameter
- Increase collagen cross-linking
effect of immobilisation
- Decrease in modulus/ ultimate stress
* Remobilisation can increase strength again and tendons/ligaments take a lot longer to do so
Tendon injuries (5)
Tendinosis (chronic inflammation)
Tendinitis (inflammation due to acute injury)
Peritendinitis (inflammation of tendon sheath)
Direct: laceration
Indirect: tendon overload
Ligament injuries
Sprain/Tear: overstretched ligaments
Treatments for injured ligaments/tendons
Rest and rehab
Suturing
Allo/Autograft
Challenges to repair (3)
Relatively avascular
Function is not easily restored due to scar tissue formation
Most injuries occur at muscle-tendon junction or bony insertion
