Microstructure and Ultrastructure Flashcards
List 6 properties of tendons
- Dense regular connective tissue
- Composed of <80% collagen (chiefly type 1) and 1-2% elastin
- Vary in size based on function
- Responsible for transmission of muscle force to bone
- Organised in bundles
- Strain resistant with up to 1260kg/cm2 tensile strength
List 4 properties of ligaments
- Similar to tendons in origin and internal structure
- Responsible for connecting bone to bone at joints
- Highly reliant on crimping regions to utilise their elasticity
- Crimping regions are also present in tendons but play a less prominent role
(Frank, 2004)
Describe the ascending organisation of tendons and ligaments
- Fibrils
- Fibres
- Primary bundles
- Secondary bundles
- Tertiary bundles
- Tendon / ligament
Describe fibrils
Composed of elongated fibroblast cells which run longitudinally, transversely and horizontally.
Bundles which run longitudinally do not always run parallel with each other; they often cross other bundles.
This structure acts as a buffer against forces acting on the tissues from all directions.
Describe the composition of a tendon exposed to higher strains
- Thicker
- Shorter
- Bigger, denser packed bundles
Describe the composition of a tendon exposed to lower strains
- Long
- Thin
- For more precise movements
What are groups of fascicles of a tendon bound by?
Epitenon (Kannus, 2000)
What is the supporting covering sheath of a ligament called?
Epiligament (Kannus, 2000)
Compare and contrast tendons and ligaments
Tendons and ligaments are viscoelastic structures.
What does this mean?
When a force is applied, the tendon or ligament will stretch to allow movement, but will always return to its original structure.
Why are tendons strong?
Why are tendons flexible?
- Strong to withstand the forces applied during muscle contraction.
- Flexible to allow movement around bone and to move under retinacula (example - long flexor tendons of the hand).
Why are ligaments strong?
Why are ligaments flexible?
- Strong to offer resistance and hold the joint together during movement.
- Flexible to allow free and natural movement of the joint (example - medial and lateral collateral ligaments of the knee joint).
What is stress?
A measure of force per unit area
What is strain?
The response of a system when stress is applied
How do you calculate strain?
Ratio: change in length over initial length
Describe normal stress
- It is assumed that the intensity of distributed forces are uniform
- Changes dimensions but not the shape of the object under stress
- Compressive stresses or tensile stresses
- δ = F/A
F = force
A = area
Describe shear stress
- Equal and opposite forces applied to opposite faces of an object
- Changes the shape of the object under stress but does not change the dimensions
- τ= F/A
Describe normal strain
- Ratio of the amount of elongation to the original length
- ϵ= Δ1/1
- If the material increases in length then strain is tensile and positive
- If the material decreases in length then strain is compressive and negative
Describe shear strain
- Related to distortions from shear stress
- Shear strain is the ratio of horizontal displacement (d) to height (h)
- Ɣ= d/h
Draw the stress vs strain curve
- O - origin
- P - proportionality limit
- E - elastic limit
- Y - yield point
- U - highest stress point
- R - rupture point
- 𝛔y - yield strength of material
- 𝛔u - ultimate strength of material
Describe the load and elongation curve
- Used to analyse biomechanical properties of tendons and ligaments
- Tissue has a tensile force applied to cause a constant rate of elongation
- This force is applied until the tissue ruptures
- There are 4 main points on the graph:
- Toe region (primary region)
- Linear region (secondary region)
- End of secondary region
- Maximum load
Descrbie the structure of the anterior longitudinal ligament
- Extends along anterolateral aspects of vertebral bodies and IV discs from pelvic surface of sacrum to anterior tubercle of C1 and occipital bone.
- Strong, thick band of collagen fibres arranged in 3 distinct layers: superficial, intermediate and deep.
- Superior part blends with the anterior atlantoaxial and atlanto-occipital ligaments.
- 1.3-2.5mm thickness range
- Well arranged bundles of collagen fibres - very stiff due to high percentage of collagen fibres.
Describe the structure of the posterior longitudinal ligament
- Lies within the vertebral canal along the posterior aspect of the vertebral bodies.
- Narrower than the ALL
- Uniform and broad in the cervical and upper thoracic regions - 10-15mm width
- Saw-toothed appearance in the lower thoracic and lumbar regions.
- Narrows over lower thoracic and lumbar vertebral bodies extending over vertebral discs.
- Collagen fibres are more compact than in the ALL
- 2x weaker than than the ALL
- In the thoracic region, ligament can withstand forces of up to 70N, but in the cervical and lumbar regions can only withstand up to 50N.
Describe the ligamenta flava
- Series of ligaments that connect adjacent laminae.
- Thin and broad superiorly thickening towards the lumbar vertebrae.
- Yellow appearance due to higher percentage of elastin than other vertebral ligaments.
Describe the supraspinous ligaments
- Cord-like structure connecting tips of adjacent spinous processes.
- Run from the tips of spinous processes from C7 to the sacrum.
- Superiorly the ligaments merge with the nuchal ligament.
- Ligaments broaden towards the lumbar region.
Describe the interspinous ligaments
- Thin, membraneous ligaments connecting adjacent spinous processes.
- Ligament is poorly developed in the neck and thickens as it descends through thoracic and lumbar vertebra.
- Anteriorly, merges with supraspinous ligaments.
Describe the intertransverse ligaments
- Ligament extends from superior border of one transverse process to inferior border of the adjacent transverse process.
- Ligaments are fibrous cords between thoracic vertebrae and become thinner and more membraneous between lumbar vertebrae.
Describe the nuchal ligament
- Thickened fibroelastic tissue.
- External occipital protuberance and posterior border of the foramen magnum to spinous processes of cervical vertebrae.
- Very high in elastin (~80%).
- Forms a midline septation dividing the posterior neck muscles.
- It is an extension of the supraspinous ligament.
Describe the transverse ligament of the atlas
- Composed of neatly arranged collagen fibres.
- Extends between the tubercles of medial aspect of the lateral masses of C1.
- Runs transversely across the anterior arch of the atlas and divides the ring into an anterior and posterior compartment.
- Can withstand a force of 350N before rupturing - largest, thickest and strongest craniocervical ligament.
- Has a smooth fibrocartilaginous surface, allowing the odontoid proess to glide smoothly against it.
Describe the alar ligament
- Used to attach the axis to the base of the skull
- Lateral aspects attach to the odontoid process
- Some believe that the superior attachment of the ligament is to the anterolateral aspect of the foramen magnum.
- Others believe that the attachment is to the medial aspect of the occipital condyles on either side.
- Mean length - 8.8mm
- Mean diameter - 7.3mm
- Can withstand 200N of force before rupturing
