Microstructure and Ultra Structure of Ligaments and Tendons Flashcards
what are the cervical spine ligaments?
Anterior and Posterior Atlanto-Occipital Membranes
Apical Ligament of Dens
Alar Ligaments
Transverse Atlantic Ligament
Cruciate Ligament of the Atlas
Tectorial Membrane of Atlanto-Axial joint
Nuchal Ligament
what are the major molecular components of both tendons and ligaments?
collagens
what is collagen?
a fibrous protein with high tensile strength.
what are the 3 types of collagen?
procollagen
tropocollagen
growing fibril
The structural hierarchy of ligaments and tendons is made up of what?
fibres, fibrils, subfibrils, microfibrils and tropocollagen but also contain water, proteoglycans and several glycoproteins.
fibroblasts are what?
the biological cells that produce the ligament or tendon via the formation of collagen.
skeletal ligaments are what and do what?
soft, densely-packed, fibrous bands of collagenous connective tissue which connects two bones, cartilage or holds together a joint
what is a ligaments function?
to guide normal joint motion when a tensile load is applied, passively maintain stability of joints and restrict abnormal or excessive joint movement.
when are the fibres recruited in a ligament?
as the joint moves
what are tendons?
soft, fibrous bands of connective tissue that connect muscle to bone
tendons are composed of what?
collagen
tendons are passive or unpassive?
passive
are tendons elastic or inelastic?
inelastic
what is the main function of tendons?
to transfer muscle generated tensile force to the bony skeleton, facilitating movement around a joint.
tendons act as what?
a mechanical pulley
what are the secondary functions of tendons?
maintain posture, stability and provide motor control.
does the arrangement of collagen fibres differ between tendon and ligament?
yes
how are ligaments organised?
in a dense but random/loose-packed network.
how are tendons organised?
highly ordered, linearly packed arrangement of bundles almost parallel to the long axis of the tendon in line with the muscle.
what are ligaments and tendons composed of ?
of fibres oriented in a parallel manner
tendons can handle what during activity?
handle higher unidirectional (uniaxial) tensile loads
ligaments handle what during activity?
generally sustain tensile loads in a predominant direction but also bear smaller tensile loads in other directions, i.e. they are anisotropic.
tendons have how much protein?
very little- type III
ligaments have how much protein?
higher ratio of Type III collagen to Type I collagen.
what are ligaments mechanical porperties?
provide it with not only the flexibility but also the tensile properties to resist force.
how much of ligaments is composed of water?
65%- 70%
type I collagen makes up what of ligaments and is responsible for what?
70-80% of dry weight, tenisle strength
type III collagen makes up what of ligaments total wight?
8% dry weight
type V collagen makes up what of ligaments?
12% dry weight
Variations in the concentrations of these basic constituents in ligaments lead to what?
different mechanical behaviors suitable for their respective functions.
The differences in collagen concentrations arise due to what?
differences in the fibroblasts and their gene expression such as reticular cells.
The ligamenta flava consist mostly of what?
dense elastic fibers
supraspinous and interspinous ligaments are predominantly made up of what?
collagenous correlating with their difference in function
The hierarchical structure of tendon and its functional properties are determined what?
by the collagens present, as well as their supramolecular organization.
load refers to what?
external force applied to the collagen.
stress refers to what?
to the amount of resistance within the collagen to the load.
strain refers to what?
is the amount of deformation that occurs in the collagen because of the load.
crimp is what?
is the waviness of the fibrils that make up the fascicles.
how many regions are ther in a stress strain curve?
3
what are the different regions of the stress strain curve?
toe region
elastic region
plastic region
what is the toe region?
represents “un-crimping” of the crimp in the collagen fibrils.
what does the toe region show?
shows a relatively low stiffness.
what happens in the toe region as the load increases?
As the load increases so does the recruitment of collagen fibres causing them to ‘uncrimp’.
what happens when collagen is stretched in the toe region?
When collagen is stretched in the toe region, it will return to its normal length when the force is removed, thus it is within its physiological range.
what kind of relationship does the toe region have on the stress strain curve
non-linear
what happens to the collagen fibrils in the linear region?
collagen fibrils become uncrimped, then we see that the collagen fibril backbone itself is being stretched in a linear relationship between deformation and load, so the tissue become relatively stiffer. collagen still returns to its original shape once the load is removed. The tissue is said to be elastic.
The continued increase in load causes what?
minor failure to the individual fibrils and damage to cross-links accumulates within the ligament or tendon and stiffness is reduced.
Stiffness is reduced because of what?
the fibrils are permanently deformed and do not return to normal length on release. The tissue is therefore ‘viscous’.
eventually what happens in the stress strain curve?
Finally, complete failure occurs as the ligament/tendon ruptures.
Tendons and ligament are viscoelastic which means what?
that their collagen demonstrates time dependent and variable elastic behaviour.
The relationship between stress and strain is what for tendon and ligaments?
not constant for tendons and ligaments but depends on the time of displacement or load.
what are the 3 major types of behaviour characteristic of viscoelasticity:
creep, stress relaxation and hysteresis or energy dissipation.
function of the ALL?
prevents hyperextension of the vertebral column
•helps to keep intervertebral joints stable
•only ligament preventing extension in vertebral column and so needs to be very stiff to combat extreme forces
structure of the ALL?
three layers
•very stiff, strong fibrous band
•portion covering anterior aspect of vertebral bodies thickest, portion covering lateral aspects of vertebral bodies and intervertebral foramen thinner (between 1.2-2.5mm in thickness)
•thicker and narrower in thoracic region compared to cervical and lumbar regions
structure of the PLL?
- 2 distinct layers
* narrower and weaker band than anterior longitudinal ligament
function of the PLL?
resists hyperflexion
•prevents and or redirects posterior herniation of nucleus pulposus
structure of the ligamenta falva?
strong, elastic and yellow (due to high percentage of elastin)
•long, thin and broad in cervical region
•thicker in thoracic region
•thickest in lumbar region
function of the ligamenta flava?
Limits flexion posteriorly
Elasticity allows laminae to separate during flexion
Elasticity also allows vertebral column to return to to upright after flexion without ligament folding
structure of the supraspinous ligament?
Adjacent spinous processes connected with shorter, deep fibers of ligament
Longer, superficial fibers of ligament span 3 to 4 spinous processes
function of the supraspinous ligament?
Limits flexion
structure of the Interspinous ligament?
Thin and membranous
(Insignificant) in cervical region, thickens and substanciates as decends down vertebral column
function of the Interspinous ligament?
Can carry up to 75% of load during flexion
Limits flexion
gross anatomy of the interspinous ligament
Attached at root and apex of each spinous process to connect them
Blends with supraspinous ligament anteriorly
gross anatomy of the intertransverse ligament
Connects adjacent transverse processes
structure of the intertransverse ligament
Cervical region - scattered fibers
Thoracic region - fibrous cords
Lumbar region - thin and membranous tissue
Can be replaced by intertransverse muscles
function of the intertransverse ligament
limits flexion
Gross anatomy of the nuchal ligament
Runs from occipital bone along spinous processes of cervical vertebrae till C7
Deep portion of ligament attaches from posterior tuberosity of atlas to all spinous processes of cervical vertebrae
structure of the nuchal ligament?
Occipital - C1: fine longitudinal tissue
C2 - C5: dorsally triangular in shape, ventrally comprised of layers; fibers orientated vertically
C6 - C7: dense connective tissue
function of the nuchal ligament?
Provides site of attachment for muscles without obstructing full range of movement in neck
Aids in holding head upright and returning head to upright position
Limits hyperflexion
gross anatomy of the Anterior Atlanto-Occipital Membrane
Passes between anterior arch of atlas to front of anterior margin of foramen magnum
Lateral margins blend w/ anteromedial part of joint capsule
structure of the Anterior Atlanto-Occipital Membrane
Dense connective tissue, fibers interwoven
Thicker in central portion due to merger with anterior longitudinal ligament
function of the Anterior Atlanto-Occipital Membrane
Prevents movements from exceeding range atlanto-occipital joint capable of
gross anatomy of the Posterior Atlanto-Occipital Membrane
Attached to posterior margin of foramen magnum and upper border of posterior arch of atlas
Merges with posteromedial aspect of joint capsule
Lateral part of attachment to atlas, membrane arches over vertebral artery and first cervical nerve as they cross this section of posterior arch
structure of the Posterior Atlanto-Occipital Membrane
Lower portion of membrane thicker
function of the Posterior Atlanto-Occipital Membrane
Prevents movements from exceeding the range of joints capacity
gross anatomy of the Accessory Atlanto-Axial Ligament
Lateral ligaments ( x 2, left and right) Runs in direct contact with posterior aspect of joint capsule Runs laterally on border of tectorial membrane
structure of the Transverse Ligament of Atlas
thickest, strongest ligament of cervical spine
6-7 mm in thickness
function of the Accessory Atlanto-Axial Ligament
Contributes to stability of cranium and cervical spine articulations
Tubbs RS et al. (2004) suggests renaming ligament to atlanto-axial-occipital ligament or accessory alar ligament
gross anatomy of the Transverse Ligament of Atlas
Medial ligament
Running from posterior aspect of dens and splits in two, attaching to small tubercle on medial sides of each lateral mass of atlas
function of the Transverse Ligament of Atlas
Stabilizing ligament
Permits rotation of atlanto-axial joint
Divides atlas into 2 compartments - separates odontoid process from spinal cord
gross anatomy of the Cruciate (or Cruciform) Ligament of the Atlas
Transverse ligament PLUS 2 x longitudinal bands of fibers
Small band of fibers ascends to attach to anterior edge of foramen magnum from medial portion of transverse ligament
Further band of fibers passes downwards to attach to body of axis
structure of the Cruciate (or Cruciform) Ligament of the Atlas
Two bands of longitudinal fibers are very thin
function of the Cruciate (or Cruciform) Ligament of the Atlas
Provide very little support in stabilizing atlanto-axial joint
gross anatomy of the Tectorial Membrane
Runs posterior to Cruciate Ligament of Atlas
Superior continuation of posterior longitudinal ligament
Runs from C2 vertebral body to floor of cranial cavity
structure of the Tectorial Membrane
3 layers which fuse at posterior longitudinal ligament, bursa present between layers over odontoid process
Most superficial - widest
Middle - thickest
Deepest layer - thins out over odontoid process
function of the Tectorial Membrane
Controversy in literature
General consensus - limits flexion
gross anatomy of the Alar Ligaments
Extended from sides of dens of axis to lateral margins of foramen magnum
Pass obliquely upwards and laterally from each side of apex of dens to medial side of occipital condyles
structure of the Alar Ligaments
Each ligament short, strong, rounded cord approximately 0.5mm in diameter
function of the Alar Ligaments
Limits rotation of joints to joint capability
gross anatomy of the Apical Ligament of the Dens
Runs between left and right alar ligaments
Band of fibers immediately anterior to superior longitudinal band of cruciate ligament of atlas
Missing in 20% of individuals
structure of the Apical Ligament of the Dens
Slender band of fibers
function of the Apical Ligament of the Dens
Controversy in literature
Appears to have little to no function in humans - considered a vestigial structure
A ligament tear or sprain is what?
an injury to the ligament caused by excessive movement beyond the normal range exerting a strain that results in failure.
Ligaments heal by a process of what?
which includes three phases: hemorrhage with inflammation, matrix and cellular proliferation and finally, remodeling and maturation.
Spinal Stenosis occurs when what?
the spinal cord or the spinal nerve roots are compressed due to narrowing of the spinal canal, the lateral recess or the intervertebral foramen.
what is a significant contributor to spinal stenosis?
ligamentum flavum
Stenosis occurs due to what?
to a combination of disk bulging, osteophyte formation on facet joints and vertebral endplates, facet joint hypertrophy and ligamentum flavum hypertrophy.
During the remodeling phase what happens?
the scar tissue formed in the matrix and cellular proliferation phase has viscoelastic properties only within 10-20% of normal ligament tissue.
The scars tend maintain a load less efficiently than normal ligament.
Ligament injuries are further complicated due to what?
by the low level of vascularity of ligaments giving them poor healing capabilities.
