Structure Of Ligaments And Tendons Flashcards
What is the tensile strength of tendons?
Up to 1260kg/cm2
What do the crimping regions of ligaments allow? (Reference?)
Allow stretch
Resist against injury
(Frank, 2004)
Describe a collagen molecule
Smallest discernible unit of tendons and ligaments
Triple helix molecule
~1nm long
Mechanically resistant due to cross-linking
Multiple types
What do collagen molecules bind into and what length are they?
Fibrils
~100nm long
Collagen fibrils can be heterogenous in composition, give an example of what this means?
Type I fibrils have collagen types I, III, IV and IX
What constitutes a collagen fibre?
Collagen fibrils plus fibroblast cells producing ECM
How long is a collagen fibre?
~1-20microm
What are collagen fibres bundled into?
Subfascicles (primary bundle)
Fascicles (secondary bundle)
Tertiary bundles
How does crossing-over in tertiary collagen bundles affect the structure?
Results in higher tensile strength
What loose connective tissue structure surrounds each collagen fibre bundle (fascicles)?
Endotenon
Endoligament
What connective tissue structure surrounds groups of fascicles?
Epitenon
Epiligament
What cells are ligaments rich in?
Proprioceptive
What is the reference for the collagen organisation of tendons and ligaments?
Wang, 2006
In what orientations do the fibrils of elongated fibroblast cells run in in tendons and ligaments?
Longitudinally
Transversely
Horizontally
In what orientation do bundles of collagen fibres run?
Longitudinally
But not always parallel = Crossing over
How do the orientation of collagen fibrils and bundles affect function? (Reference?)
Serves to buffer against forces acting on these tissues from different directions
(Kannus, 2000)
How can the structure of tendons under higher strains be described?
Thicker
Shorter
Bigger and denser packed bundles
How can the structure of tendons under low strains be described and how does this affect the movements they are parts of?
Longer
Thinner
Used in more precise movements
What is an epitenon/epiligament?
Loose connective tissue sac acting as a supporting sheath and fill with synovial fluid
What is paratenon? What is its function?
The very outer layer Loose mesenchyme which carries: - Blood vessels - Lymphatics - Nerves Also assists in sliding
How much water is in the ECM of ligaments and how much in tendons?
60-80% water in ECM of both
How can the elasticity of both ligaments and tendons be described?
Ligaments = Stretchy Tendons = Rigid
What is the level of organisation of collagen fibres in both ligaments and tendons?
Ligaments = Less organised fibres Tendons = Highly organised fibres
What type(s) of collagen are present in both ligaments and tendons? (Reference?)
Ligaments = Type I most common but also Type III (Frank, 2004) Tendons = Type I collagen chiefly (Kannus, 2000)
What is the DNA content of ligaments and tendons? What does this affect? (Reference?)
Ligaments = Higher DNA content so higher metabolic function
Tendons = Lower DNA content
(Amiel et al., 1984)
How much elastin is present in ligaments and tendons?
Ligaments = ~10% (up to 80% in nuchal ligament) Tendons = ~2%
What is the peptidoglycan content of the ECM in ligaments and tendons?
Ligaments = Higher Tendons = Lower
In what ligaments is the elastin level lower than the average level? What percentage is elastin present at in these?
Spinal ligaments = ~7% elastin (vs 10%)
When ligaments regenerate, what percentage of their original strain resistance do they retain and why?
10-20% original strain resistance
Cross-linking causes scarring
Tendons and ligaments are viscoelastic, what does this mean?
When a force is applied, they stretch to allow movement and will return to original structure
Why are tendons strong?
To withstand forces during muscle contraction
Why are tendons flexible?
To allow:
- Movement around bone
- Movement under retinacula
Why are ligaments flexible?
Offer resistance to movement
Hold joint together during movement (MCL and LCL)
What is the reference for the mechanics (strength and flexibility) of tendons and ligaments?
Nordin and Frankel, 2001
What are stress and strain?
Stress is a measure of force
Strain is the response of a system when stressed
What is strain a ratio of?
Change in length over initial length
What is the unit for stress?
N/m2 or Pa
Stress = Force/Area
Describe normal stress
Intensity of distributed forces are uniform
Dimensions change but not shape
Compressive or Tensile force
Symbol is delta
Describe shear stress
Equal and opposite force applied to opposite force (e.g. Book on table)
Changes shape of object but not dimensions
Symbol is tau
What is strain a measure of?
Deformation of a material
What is normal strain?
Ratio of amount of elongation to original length Normal strain (E) = Change in length/Original length
If there is an increase in length, how is strain described?
Strain is tensile and positive
If there is a decrease in length, how is strain described?
Strain is compressive and negative
What is shear strain?
The ratio between horizontal displacement (d) and height (h) Shear strain (gamma) = d/h
What is point P on the stress-strain curve?
Proportionality limit = Up to this point, stress is proportional to strain (Hooke’s law)
What is point e on the stress-strain curve?
Elastic limit = Point of stress at which all strain will totally disappear if force removed
What is point y on the stress-strain curve?
Yield point = Smallest amount of stress that will cause permanent plastic deformation