V.C - E - Microstructure & Ultrastructure of Ligaments & Tendons, Stress Strain Curve, Ligament tear and Spinal stenosis Flashcards
What is the major molecular component of both ligaments and tendons?
Collagen is the major molecular component of ligaments and tendons
Let us talk about the formation of the collagen fibres which are the major components of ligaments and tendons Pre-procollagen is translated form mRNA (messenger RNA) on ribosomes and is carried to the endopasmic reticulum where it is further processed to become procollagen What is procllagen and how does it become tropocollagen?
Procollagen is a triple helix molecule with ‘loose’ terminal endings The terminal endings of procollagen are removed by the procallagen peptidase enzyme that now forms tropocollagen
Procollagen is a triple helix molecule with ‘loose’ terminal endings which is cleaved by procllagen peptidase to form tropocollagen Describe tropocollagen? What do multiple tropocollagens binding together form?
Tropocollagen is a ‘cleaned’ triple helix molecule which binds with other tropocollagen molecules into a polymer called a collagen fibril
Finally, fibril bundles are “spun together” into collagen fibres, which make up the (many various) collagen structures the body needs. Describe how pre-procollagen (translated from messenger RNA) becomes a collagen fibre?
- Pre-procollagen is transported to the endoplasmic reticulum where it is processed to become procollagen (a triple helix molecule with ‘loose’ terminal endings)
- Procollagen is hydrolyzed by procollagen peptidase to form the ‘clean’ triple helix molecule - tropocollagen
- Tropocollagen binds with other tropocollagen molecules to form a polymer called a collagen fibril
- Fibril bundles are ‘spun together’ to form collagen fibres
How many polypeptides are procollagen and tropocollagen formed from?
Both procollagen and tropocollagen are formed from three polypetides winding together to form the triple helix Three polypeptides coil to form tropocollagen. Many tropocollagens then bind together to form a fibril, and many of these then form a fibre.”
The structural hierarchy of ligaments and tendons is made up of fibres, fibrils, subfibrils, microfibrils and tropocollagen but also contain water, proteoglycans and several glycoproteins. What are the cells that produce the ligament or tendon via the formation of collagen?
The fibroblasts are the cells that produce the tendons and ligaments via the formation of collagen
What is the wave-like configuration of the fibril known as?
The wave-like configuration of the fibrils which join together is known as a the crimp of fibril
What does the crimp of the fibril allow for? - remember the crimp of the fibril is the wave like configuration of the fibrils when joined together
The crimp of the fibril allows for the stretching of the tendons and ligaments
What do ligaments connect? Are skeletal ligaments Hard? Densely packed? Cartilaginous?
Skeletal ligaments are soft, densely pack fibrous bands or collagenous tissue that connects two bones, cartilage or holds a joint together
What is the orientation of the collagen fibres in a ligament?
Bundles of collagen fibres are orientated in a parallel fashion and fibres are recruited as the joint moves (other fibres are woven between the parallel fibres to enable the ligament to resist loads in more than one direction)
What is the mechanical function of the ligament? (when both a tensile load is applied and when the joint is passive)
Mechanical function of a ligament is to guide normal joint motion when a tensile load is applied and passively maintain stability of the joint and restrict abnormal or excessive movement of the joint
* Describe a ligament * What is the orientation of the collagen fibres in a ligament? * What is the mechanical function of the ligament? (when both a tensile load is applied and when the joint is passive)
A skeletal ligament is soft, densely packed fibrous bands or collagenous connective tissue which connects two bones, cartilage or holds joints together Collagen fibres are orientated in a parallel fashion and are recruited as the joint moves (other fibres are woven between to resist loads in more than one direction) The mechanical function of the ligament is to guide normal joint motion when a tensile load is applied, passively maintain stability of a joint and restrict abnormal or excess joint movement
Tendons are soft fibrous bands of connective tissue What do tendons connect? What are tendons predominantly composed of? Are tendons or ligaments more elastic?
Tendons connect muscle to bone Tendons are predominanlty composed of collagen Tendons are more inelastic than ligaments
Tendons are relatively passive, inleastic structures able to resist high forces What is the main function of a tendon?
The main function of a tendon is to transfer muscle generate tensile force to the bony skeleton to facilitate movement around a joint
Tendons also act as a mechanical pulley What is the secondary function of a tendon?
To maintain posture, stability and provide motor control
* Describe a tendon * What are tendons predominantly composed of * What is the main function of a tendon? * What do tendons connect? * Are tendons or ligaments more elastic? * What is the main function of a tendon? Tendons also act as a mechanical pulley * What is the secondary function of a tendon?
Tendons are soft bands of fibrous connective tissue that is predominantly composed of collagen. They are relatively passive, inelastic, structures able to resist high forces. * Tendons connect muscle to bone and are more inelastic than ligaments * The main function of a tendon is transfer muscle generated tensile load to the bony skeleton to facilitate movement of the joint * The secondary function of a tendon is to maintain posture, stability and provide motor control
How does the arrangement of collagen fibres differ between tendons and ligaments?
The ligaments are arranged in a dense but random/loose network with the collagen fibres appearing to be in a parallel fashion with fibres woven between The tendon fibres have a highly ordered, linearly packed arranged of bundles almost parallel to the long axis of the tendon in line with the muscles
Ligaments and tendons are composed of fibres oriented in a parallel manner Are both ligaments and tendons able to bear loads in any direction? Are tenonds/ ligaments anisotropic or isotropic?
Tendons can handle higher unidirectional (uniaxial) loads during activity (isotropic) Ligaments on the other hand generally sustain tensile loads in a predominant direction but can bear smaller tensile loads in other directions also (anisotropic) Tendons can bear loads in one direction - isotropic Ligaments can bear loads in other directions - anisotropic
Do ligaments or tendons generally sustain higher tensile loads? What type of collagen do both ligaments and tendons mainly contain?
Tendons can generally sustain higher tensile loads than ligaments but only in one direction * Tendons lack the elastic type III collagen and are composed of mainly Type 1 collagen * Ligaments on the other hand have a higher type III to type I collagen ratio A ligament’s mechanical properties provide it with not only the flexibility but also the tensile properties to resist force.
We know that the dry mass of tendons is composed of mainly type I collagen (>95%) Lets talk about the composition of ligaments What percentage of a ligaments total body weight is water?
65-70% of a ligaments total body weight is water
With 65-70% of the ligaments total body weight being water, what is the main constituents of the ligaments dry weight? (State the percentages) Also which constituents accounts for the ligaments strength?
The main constituent of the ligaments dry weight is:
- Type 1 collagen - 75-80% of the dry weight - accounts for the ligaments strength
- Type III collagen - 8% of the dry weight
- Type V collagen - 12% of the dry weight
As said, it is the variation in the collagen concentrations of the ligament that lead to different mechanical patterns suitable for their functions What is the difference in collagen concentrations due to?
The differences in collagen concentrations is due to differences in the fibroblasts and their gene expression such as reticular cells
Each ligament’s composition is directly correlated with its mechanical properties. What is the difference in the composition of the ligamentum flavum compared to the supraspinous and interspinous ligaments?
The ligamentum flavum is composed of mainly dense elastic tissue whereas the supra and interspinous ligaments are predominantly collagenous
Time to discuss the STRESS-STRAIN CURVE Firstly we must define stress and strain Define them Also define crimp
Stress - this is the amount of resistance within the collagen to the load placed on it Strain - this is the amount of deformation that occurs in the collagen due to the load * The higher the stress, the more the strain * The higher the resistance, means the greater the load, means the greater the deformation in the collagen Crimp is the waviness of the fibrils that make up the fascicles
Define stress and strain again? What are the three main regions of the stress strain curve?
Stress - this is the resistance of the collagen to the load placed on it
Strain - this is the amount of deformation that occurs in the collagen due to the load
The three main regions of the stress strain curve are: * Toe region * Elastic (linear) region * Plastic region
Describe the toe region of the stress strain curve?
The toe region represents the uncrimping of the crimp in the collagen fibrils This shows that as the load increases, so does the recruitment of collagen fibres causing them to uncrimp
When the collagen fibres are stretched in the toe region, are they able to return to their normal shape? Is the relationship in the stress strain curve linear or non-linear at this stage? Is the toe-region of the curve showing a high or low stiffness?
When the collagen fibres are stretched in the toe-region, they will return to their normal length when the force is remove The relationship in the stress-strain curve is non-linear at the toe-region stage This part of the stress strain curve shows a relatively low stiffness
After the toe-region, what is the next step in the stress-strain curve? Describe this region? Can the fibres return to their normal length?
After the collagen fibres become uncrimped, the collagen fibril backbone itself itself is stretched in a linear relationship between deformation (strain) and load (stress) This is described as the elastic region as the fibres can return to their original shape once the load is removed
What is the point at which there is too much strain on the ligament for the ligament to return to its original shape once the load is removed known as?
This is the Yield point After the Yiel point - we enter the Plastic Region
Once the stiffness is reduced because the fibrils are permanently deformed and cannot return to their normal length on release - what is the tissue now known as? What is the failure point on the stress strain curve?
The stiffness is reduced because the fibrils are permanently deformed and cannot return to their normal length on release - the tissue is therefore now viscous The failure point on the stress-strain curve is when complete failure occurs and the ligament/tendon ruptures
What is creep, hysteresis and stress-relaxation? Hysteresis - aka energy dissipation
https://s3.amazonaws.com/classconnection/403/flashcards/11907403/png/ppngjpgpngjpg-167FAFE7AB9519CB949.png
We have talked about the microstructure of ligaments/tendons Time to talk about the gross anatomy, ultrastructure and function of the individual ligaments Where does the anterior longitudinal ligament attach? What do the fibres span?
The anterior longitduinal is made of 3 layers of dense collagen fibres running on the anterolateral aspects of the vertebral bodies - the superficial fibres span multiple vertebral segments and the deep fibres bind adjacent vertebrae together The ALL attaches from the anterior portion of the occipital bone anterior to the foramen magnum, the anterior tubercle of C1 to the pelvic portion of the sacrum
What do the fibres of the ALL blend with superiorly? What aspect of the ALL covering the vertebral body is thicker and which is thinner? Which region has thicker and narrower fibres?
The fibres of the ALL blend with the anterior atlanto-occipital membrane The ALL fibres thicker on the anterior aspect of the vertebrae and thinner on the lateral aspect The fibres are also thicker and narrow in the thoracic region
What is the function of the anterior longitudinal ligament?
The ALL Limits hyperextension of the vertebral column- as it is the only ligament preventing extension - it is very strong and stiff It also helps to stabilise the intervertebral joints
What is the function of the posterior longitudinal ligament?
The PLL resists hyperflexion and prevents or redirects posterior herniation of the IV disc
What is the function of the ligamentum flavum?
It helps reinforce the vertebral canal posteriorly It limits flexion of the vertebral column It maintains vertebral curvatures The elasticity allows the laminae to separate during flexion
We have discussed the gross anatomy, ultrastructure and function of the ligaments of the vertebral column Now to discuss the cervical spine ligaments What is the attachment of the nuchal ligament? Include deep portion attachment
The nuchal ligament runs from the external occipital protuberance and posterior border of the foramen magnum to the spinous process of C7 The deep portion attaches from the posterior tubercle of the atlas to the spinous processes of all cervical vertebrae
What is the function of the nuchal ligament?
It serves as a site of muscle attachment without obstructing full range of movement in the neck It limits hyperflexion o f the neck It aids in holding the head upright and returning the head to its normal position
What is the membrane which the anterior longitudinal ligament blends with superiorly? Where does this membrane attach?
The anterior longitudinal ligament blends superiorly with the anterior antlanto-occipital membrane The anterior antlanto-occipital membrane attaches form the anterior arch of the atlas to the anterior margin of the foramen magnum
Describe the structure of the anterior antlanto-occipital membrane Where is the anterior atlanto-occipital membrane thicker? What is the function of the anterior atlanto-occipital membrane again?
The anterior antlatno-occipital membrane is dense connective tissue with interwoven fibres It is thicker centrally due to the merger with the ALL The function of the membrane is to prevent movements exceeding the range of the atlanto-occipital joint
What is the attachment of the posterior antlanto-occipital membrane? Similar to the anterior part of the membrane What does the posteiror atlanto-occipital membrane merge with?
The posterior atlanto occipital membrane attaches from the upper border of the posterior arch of the atlas to the posteiror margin of the foramen magnum The membrane merges with the posteromedial aspect of the joint capsule
The lateral part of the posterior atlanto occpital membrane that attaches at the posteiror arch of the atlas arches over vessels here. What are these vessels? Which aspect of the membrane is thicker? What is the function of the posterior atlanto occpital membrane? (similar to the anterior)
The lateral part of the posterior atlanto-occipital membrane arches over are the first spinal nerve and the vertebral artery as they cross this section of the posterior arch The lower portion of the membrane is thicker The membrane functions to prevent movements exceeding the capability of the atlanto-occipital joint
Describe the accessory atlanto-axial ligaments Where do they run?
The accessory atlanto axial ligaments (left and right) run directly on the posterior aspect of the joint capsule on the lateral border of the tectorial membrane
What is the function of the accessory atlanto-axial ligament?
Contributes to the stability of the cervical spine articulations and cranium
What is the thickest strongest ligament of the cervical spine and where does it run form?
The strongest ligament of the cervical spine is the transverse ligament of the atlas It runs from the posterior aspect of the dens and splits into two inserting on small tubercles on the medial sides of the lateral masses of the atlas
What is the function of the transverse ligament of the atlas?
It is a stabilizing ligament permitting rotation of the atlantoaxial joint (synovial pivot joint) and separates the spinal cord from the odontoid process
What is the name of the ligament formed form the transverse ligament + 2 longitudinal fibres?
This would be the cruciate (or cruciform) ligament of the atlas
What is the attachment of the longitduinal fibres of the cruciate ligament? What is the function of the cruciate ligament?
The superior longtiuinal band of fibres ascends to attach to the anterior edge of the foramen magnum The inferior longitudinal band of fibres descends to attach to the body of the axis The function of the cruciate ligament is to further stabilise the atlatno-axial joint
What ligament runs posterior to the cruciate ligament of the atlas? What is it a superior continaution off? Where does this ligament attach?
The ligament running posterior to the cruciate ligament is the tectorial membrane of the atlanto-axial joint It is a superior continuation of the posterior longitduinal ligament It attaches from C2 vertebral body to the floor of the cranial cavity
What exists between the layers of the tectorial membrane as it passes over the odontoid process? What is the difference in structure of the three layers? What is the general consensus of the function of the tectorial membrane?
Between the tectorial membrane and odontoid process is a bursa The most superficial layer of the tectorial membrane is the widest The middle layer is the thickest The deepest layer thins out over odontoid process The function is to limit flexion of the neck
What are the attachments of the alar ligaments?
The alar ligaments arise at the sides of the dens and extend oblqiuely upwards and laterally to the lateral margins of the foramen magnum and the medial side of the occipital condyles
Describe the structure of the alar ligaments and their function?
They are strong, short rounded cords which resist axial rotation of the neck
What is the ligament existing between the right and left alar ligaments? What do its band of fibres sit immediately anterior to? What are its attachments?
The small apical ligament runs between the right and left alar ligaments from the tip of the odontoid process to the foramen magnum Its band of fibres run anterior to the superior longitduinal band of fibres of the cruciate ligament
What is the function of the small apical ligament?
It is considered to have no function in humans -vestigial structure
A ligament tear or sprain is an injury to the ligament caused by excessive movement beyond the normal range exerting a strain that results in failure. Injury to a ligament results in a drastic change to its structure and physiology. To attempt to restore a ligament’s function, scar tissue is formed that that is inferior to the original tissue. What are the three phases of the ligament healing process?
* Haemorrhage with inflammation * Matrix and cellular proliferation * Remodelling and maturation
As the scar tissue only has the viscoelastic properties 10-20% of normal ligamentous tissue, it maintains a load less efficiently What is a further problem making ligament healing difficult?
Ligamentous injuries are further complicated by the low level of vascularity giving them poor healing capabilities
When does spinal stenosis occur? Which ligament is a significant contributor to spinal stenosis?
Spinal stenosis occurs when the spinal cord or spinal nerve roots are compressed due to narrowing of the spinal canal, the lateral recess or the intervertebral foramen The ligamentum flavum is a significant contributor to spinal stenosis
Ligamentum flavum literally means “yellow ligament,” and is so known because it has a yellow coloring due to the amount of elastin (a springy type of collagen). The elastin pulls the ligament out of the canal when the spine is extended. What happens to the elastin with age?
As we age, the ligament loses elastin and this allows the ligament to encroach on the spinal canal when returning from a position and therefore the ligamentum flavum is usually removed during a lumbar decompression surgery
The ligamentum flavum acts as a covering over the spinal canal but as we age, the ligament hypertrophies (thickens), encroaching and narrowing the lumbar spinal canal due to elastic fiber misalignment and developing calcification What are other causes of spinal stenosis?
Stenosis occurs due to a combination of bulging disc, osteophyte formation on facet joints and vertebral end plates and ligamentum flavum hypertrophy
