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
What is point u on the stress-strain curve?
Highest stress point
What is point r on the stress-strain curve?
Rupture
What is stress relaxation?
When a material is held at a constant strain, the stress required to do so decreases over time
What is creep?
When a material is held at a constant stress, the strain increases over time
What is the reference for stress relaxation and creep?
Matucci, 2012
How is a load and elongation curve recorded for a tendon or ligament?
Tissue has a tensile force applied to cause a constant rate of elongation and this is applied until the tissue ruptures
What is the first part of a load and elongation curve?
Toe/Primary region = Tissue elongated with a small increase in load as ‘wavy’ collagen straightens out
What is the second part of a load and elongation curve?
Linear/Secondary region = Fibres straight. Stiffness increases and deformation begins
What is the third part of a load and elongation curve?
End of secondary region = Load at this point is the limiting load (Plim). Progressive collagen failure after this point
What is the fourth part of a load and elongation curve?
Max load = (Pmax). Ultimate tensile strength. Complete failure is rapid
What is the reference for the load and elongation curve?
Nordin and Frankel, 2001
How do the ligaments affect the vertebral column and its contents?
Range of movement limited by resistance of ligaments
Ligaments provide support and protection for Spinal Cord while maintaining mobility
Where does the anterior longitudinal ligament run from and to?
From pelvic surface of sacrum
To:
- Anterior tubercle of C1
- Occiput
Describe the layers of the anterior longitudinal ligament?
Superficial = Longest fibres (span 3-5 vertebrae) Intermediate = Span 2-3 vertebrae Deep = Extend over 1 vertebral body and blend with periosteum
What does the superior part of the anterior longitudinal ligament blend with?
Anterior atlantoaxial ligament
Atlanta-occipital ligament
How thick is the anterior longitudinal ligament and how well arranged are the collagen bundles?
1.3-2.5mm thick
Well arranged
What are the references for the structure of the anterior longitudinal ligament?
Moore et al., 2010
Florian-Rodriguez et al., 2017
What are the functions of the anterior longitudinal ligament?
Maintain vertebral column stability between individual vertebral joints
Restrains movement of each vertebral segment - limiting extension
Why is the anterior longitudinal ligament very stiff?
Due to high % of collagen fibres
What is the reference for the functions of the anterior longitudinal ligament?
Butt et al., 2015
True or false - The ALL is the strongest and longest vertebral ligament?
True
Why is the posterior longitudinal ligament narrower than the ALL?
Lies within vertebral canal on posterior aspect of vertebral bodies
What is the structure of the PLL in the cervical and upper thoracic regions?
Uniform
Broad (10-15mm)
What is the appearance of the PLL in the lower thoracic and lumbar regions?
Saw-toothed
What happens to the PLL as it descends over the lower thoracic and lumbar vertebral bodies?
Narrows as vertebral bodies increase in size
How do the collagen fibres in the PLL compare to those in the ALL?
More compact than in ALL
What are the references for the structure of the PLL?
Moore et al., 2010
Butt et al., 2015
What are the functions of the PLL?
Prevents separation of posterior aspects of VBs - limiting Flexion
Avoids posterior IV disc herniation
How much stronger/weaker is the PLL than the ALL? What forces can the PLL withstand?
2x weaker than ALL
Can withstand:
- 70N in thoracic regions
- 50N in cervical and lumbar regions
What are the references for the functions of the PLL?
Butt et al., 015
Tubbs et al., 2007
What is the structure of the ligamenta flava?
Connect adjacent laminae
Thin and broad superiorly
Thickens towards lumbar region
Higher % of elastin than other vertebral ligaments (appears yellow)
What are the functions of the ligamenta flava?
Counteracts vertebral lamina separation during Flexion
Helps return vertebral column to upright position after Flexion
What does the elastic quality of the ligamenta flava prevent?
Buckling
What is the course of the supraspinous ligaments? What does it blend with superiorly and how does its structure change inferiorly?
Runs from tip of spinous process of C7 to sacrum
Blends superiorly with nuchal ligament
Broadens towards lumbar region
What are the references for the structure of the supraspinous ligament?
Moore et al., 2010
Johnson and Zang, 2002
What are the functions of the supraspinous ligaments and when does it hold its maximum load?
Limits Flexion
Resists separation of spinous processes
Holds max load during torsion
- When vertebral column rotates
What is the structure of the interspinous ligaments? Where is is small and where is it thicker? What does it merge with?
Thin membranous ligament between spinous processes
Poorly developed in cervical region
Thickens as it descends through thoracic and lumbar regions
Merges anteriorly with supraspinous ligament
What are the functions of the interspinous ligaments?
Works with ligamentum flavum and supraspinous ligaments
Vertebral stability
Limited resistance to flexion
Counteracts separation of spinous processes
What is the appearance of the intertransverse ligaments?
Fibrous between thoracic vertebrae
Thinner and more membranous between lumbar vertebrae
What are the functions of the intertransverse ligaments?
Limit Flexion
Carry max load during lateral flexion of vertebral column
What is the course of the nuchal ligament?
From external occipital protuberance and posterior border of foremen magnum
To spinous processes of cervical vertebrae
What is the elastin content of the nuchal ligament?
~80%
How does the nuchal ligament divide the posterior neck muscles?
By forming a midline septation
What are the references for the structure of the nuchal ligament?
Moore et al., 2010
Kerr, 2010
Tubbs et al., 2011
What are the functions of the nuchal ligament?
Supports the head Resists hyperFlexion of cervical spine Returns head to anatomical position Helps maintain c-spine alignment Muscle attachment (due to broad lateral surfaces)
Why is the nuchal ligament thicker in quadrupeds?
They must hold their head up while on all fours
What is the structure of the transverse ligament of the atlas?
Extends between tubercles on medical aspects of lateral masses of C1
Running transversely across anterior arch of atlas
What does the transverse ligament of the atlas divide the vertebral canal into and what structures run through each?
Anterior compartment = Dens
Posterior compartment = Spinal Cord and CN XI
How much force can the transverse ligament of the atlas support? What does this say about it?
350N
It is the largest, strongest and thickest craniocervical ligament
What does the smooth anterior fibrocartilage surface of the transverse ligament allow?
The odontoid process to glide against it
What are the functions of the transverse ligament of the atlas?
Contributes to craniocervical joint stability (strongest)
Aids stabilisation of atlantoaxial joint
Permits rotation of atlantoaxial joint
Limits Flexion at:
- Atlanto-occipital joint
- Atlantoaxial joint
Prevents anterior displacement of axis by pushing ventral surface of dens against posterior aspect of the anterior arch of atlas
What are the references for the structure and functions of the transverse ligament of the atlas?
Panjabi et al., 1998
Tubbs et al., 2011
Where do the lateral aspects of the alar ligament attach?
Odontoid process
What are the potential superior attachments of the alar ligament?
Anterolateral aspect of foremen magnum
OR
Medial aspects of occipital condyles
What are the mean dimensions of the alar ligament?
Mean length = 8.8mm
Mean diameter = 7.3mm
How much force can the alar ligament resist before rupturing?
200N
What joints does the alar ligament stabilise?
Atlantoaxial joint Craniocervical junction (with transverse ligament)
What movements does the alar ligament resist?
Excessive rotation (at atlantoaxial and atlanto-occipital joints) Lateral bending (contralaterally) Anterior displacement of atlas
What can cause alar ligament damage and what can it result in?
RTAs
Results in further axial rotation causing compression/damage to:
- Vertebral artery
- CN XI
What are the references for the alar ligament structure and function?
Iwanaga et al., 2017
Panjabi et al., 1998
Sardis et al., 2017
Tubbs et al., 2011
How much can ligaments stretch beyond their original length before disruption? What happens after this point? At what percentage is there complete rupture?
Can stretch up to a max of 4% beyond original length
Strain >4% = Rupture of up to 50% of fibres and moderate tearing
Complete rupture at 20% which may also damage connected structures
Why are crosslinked fibres susceptible to tearing?
Ageing > Crosslinks mature > Regen with scarring > Reduced strain resistance
What can cause a rupture of the transverse ligament of atlas?
Falls/accidents with direct blow to head and forced hyperFlexion
When the transverse ligament of the atlas tears, where in the ligament is most susceptible to tearing?
The body of the ligament
Why are ruptures of the transverse ligament of the atlas rare in kids? (Reference?)
Weaker synchondrosis of dens compared to ligament
Floman et al., 1991
What can result in rupture of the alar ligament?
RTAs resulting in:
- Hyperextension
- Excessive rotation
Why are ligaments of the craniocervical junction susceptible to high energy injuries?
High % of collagen content
Little stretch due to low elastin
What are the references for ruptures of the craniocervical ligaments?
Mesfar and Moglo, 2913
Kaufmann et al., 2015
Tubbs et al., 2011
How can ossification of the PLL and ligamentum flavum affect the Spinal Cord? How does this present? (Reference?)
Compress Spinal Cord Causes: - Neck pain - Limb dysfunction (Jian et al., 2011)
In what individuals is ossification of the PLL and ligamentum flavum more common? (Reference?)
Females (Tsuyama, 1981)
Asians (Wang et al., 2017)
After what surgery in what region is ossification of the PLL a significant risk?
Atlantoaxial fusion after lower lumbar spine surgery
