List the differences in structure between tendons and ligaments
- Ligaments: Have more elastin
- Collagen fibres more randomly organised
- Have larger diameter fibres
- Uniform insertion into bone
What is the structure of tendon, macro and micro?
Large parallel fibres with uniform insertion into bone. Endotenon continues into bone/periosteum and perimysium.
- It is composed of:
- Endotenon: Connective tissue that wraps around fascicles and keeps them together
- Allows longitudinal movement of fascicles
- Paratenon: Surrounds tendon
- Its vascularised connective tissue
- Epitenon: Produces synovial fluid,
- It lies under paratenon at high friction locations.
Give an example where tendon structure depends on location and function
hands: Flexors are oval, etensors are flat and thin out into sheet-like expansions
Explain the difference in structure between vascular and avasuclar tendons. Where do you find avasuclar tendons?
- Vascular tendons: Move in a straight line and are surrounded by paratenon
- Avascular tendons: Surrounded by tendon sheath. You get higher compressive stresses here. Find avascular ones wrapped around a joint
What is the structure of ligaments?
- Smaller diameter fibres
- More randomly organised collagen fibres
- Parallel or interwoven
What is the function of tendons and ligaments respectively?
Tendons connect bone to muscle and transmit forces from muscle to bone.
Ligaments connect bone to bone and stabilise joints to prevent excessive motion
Explain the heirarchical structure of tendons and ligaments
Tropocollagen molecules are woven together to form microfibrils to form fibres to form subfascicles to form fascicles into tendons/ligaments
- Fascicles are separated by fascicular membrane . Tissue is separated by reticular membrane
How do ligaments get nutrients. Why this way?
- They have poor vascularisation so microvessels from insertion site provide nutrition
- Important to maintain process of matrix synthesis and repair.
How do ligaments insert? (two ways)
- Direct insertion: The superficial fibres join periosteum
- Deep fibres join in bones in the order- Ligament, fibrocartilage, mineralised fibrocartilage, bone
- Indirect :Superficial fibres join periosteum but you get few deep fibres
What are the components of tendons and ligaments?
- Rod shaped fibroblasts arranged in rows
- Matrix: Water, collagen 1&3, Ground substance, elastin
Draw the mechanical model for non linear loading of tendons/ligaments
Draw the deformation vs force graph of collagen fibrils and include all the necessary regions, explaining them
Toe region: Stretches easily due to straightening of crimped collagen fibrils. Fibres reorient in the direction of loading
Linear region: Elastic strain energy recovered: 95%
- Yield and failure region: Failure occurs in an unpredictable manner.
Why is determining failure of ligaments or tendons so difficult?
Faliure normally occurs at the grips
What are material properties dependent on? Which ones are we interested in?
Independent of geometry
Determined from stress strain relationship
We are interested in: UTS, Modulus of elasticity, Strain energy density, Ultimate strain
What are structural properties dependent on, and which ones do we care about?
Mechanical properties as a whole.
Determined from load and deflection
We want: Ultimate load, stiffness, energy absorbed, ultimate elongation
Dependent on: Geometry of tissue, Properties of tissue-bone interfaces
Which tissue has the highest tensile strength of any soft tissue?
Tendon. 3x stronger in tension than muscle
What are the challenges with mechanical testing? List solutions to these problems
- Short specimen due to area lost to grips.
- Solution is to keep bone attached if possible.
- Another problem is slipping.
- Solution: freezing, sutures, wires, wrapping
What methods are there to measure strain?
Contact: Extensors with serrations or teeth
Non contact: Optical markers along tendon tracked with image correlation
What advantages are there to non contact methods of measuring strain?
No slippingof transducer, no distortion of tissue, non-invasive to tissue
What methods are there to measure cross sectional area?
Contact: Digital Callipers, moulding methods
Non contact: Laser micrometers
What factors affect biomechanics of ligaments and tendons
- Proteoglycan content
- Elastin content
- Specimen orientation
- Levels of stress experienced
- Strain rate: Viscoelasticity
Remember to TeSt HyProCom ViElOr
What is Viscoelasticity: Creep? Draw a damn graph for it
Increasing deformation under constant load
Eg isometric contraction: Tendon stretches, muscle contracts, muscle/tendon length is constant
What are the effects of aging on collagen?
- Stiffness and elastic modulus increase up until skeletal maturity
- Cross link number and quality increase
- Collagen fibril diameter increases
- Decrease in ultimate load
What happens with increased cyclic loading of ligaments?
- Stress decreases with protects ligament from fatigue failure.
- Fatigue can occur at lower load than required in a single application