V.C - D - Biomechanics of the Vertebral body - Cortical bone & thickness, trabecular bone & systems, cartilaginous end plate Flashcards
The vertebral column articulates superiorly with the skull and ends inferiorly at the sacrum articulating with the coccyx and the hip-bones within the pelvic girdle How many vertebrae are there and what are the 5 different regions?
33 vertebrae in total Cervical - 7 Thoracic - 12 Lumbar - 5 Sacral - 5 Coccygeal - 4
As the cervical vertebrae are not significant weight bearing bones, they are smaller in size than those in the thoracic and lumbar spine. What measurement are the cervical vertebral body wider (C3-7) - anteroposteriorly or transversely? How do the superior and inferior surfaces of the body differ in shape?
The cervical vertebral body (C3-C7) are said to be wider transversely than anteroposteriorly The superior surface of the C3-7 vertebral bodies are concave due to the presence of the hook shaped uncinate processes The inferior surface of the C3-7 bodies are convex
What is the strongest cervical vertebrae and what does it allow for due to its unique structure? What is the load bearing part of the axis?
This would be the axis - it allows pivoting off the head due to its unique odontoid process (pivoting is movement around one axis) The flat articular surfaces on the superior articular facets are the weight bearing aspect of the axis
What does the atlas posses which acts as its weight bearing feature due to the fact it has no vertebral body?
Instead of the vertebral body to act as the weight bearing structure in the atlas, it has its lateral masses which sit slightly anteriorly and medially
The adult vertebral body is formed from the developed of the juvenile centrum and the boutons of the pedicles Which part of the thoracic vertebral body do the ribs articulate with?
The ribs articulate with the part of the adult vertebral body that developed from the boutons of the pedicles
How is the lumbar vertebrae ideal for weight bearing purposes?
The lumbar vertebral body has flat superior and inferior surfaces meaning it is ideal for resisting longitduinal (axial loading) forces applied to them The flat surfaces of the body means the lumbar vertebrae lack features that stop sliding - could lead to spondylolisthesis This means the lumbar vertebral bodies rely solely on other structures within the vertebral columns, like ligaments, for stability.
The types of bone making up the lumbar vertebral bodies significantly affect the way the bone can weight bear. What is the difference in the types of bone in the lumbar vertebral body?
The lumbar vertebral body has an outer cortical shell with cancellous bone deep to it The cancellous bone allows for dynamic compress where the cortical bone would just fracture if it were exposed to this alone
The sacrum is made up of five fused vertebrae therefore no defined vertebral body. Why is the sacrum significantly smaller inferiorly?
The sacrum is significantly smaller inferiorly as it is not weight bearing here
What is bone composed of?
Bone is composed of * 65% Mineral salts (hydroxyapatite) * 23% collagen * 10% water * 2% non collagen proteins
Bone is composed of * 65% Mineral salts (hydroxyapatite) * 23% collagen * 10% water * 2% non collagen proteins What is the purpose of the hydroxyapatite and collagen in bone?
65% of bone is composed of mineral salts (hydroxyapatite) - this provides the bone with hardness and rigidity 23% of bone is composed of collagen - this provides the bone with elasticity and strength
What is the fibrous and osteogenic outer layer of bone known as?
This fibrous and osteogenic outer layer of bone is known as the periosteum
In bone, there is the outer cortical layer - dense and compact and the inner cancellous (trabecular) layer - porous What is the main role of the cortical bone? What is the functional unit of the cortical bone?
The main role of the cortical bone is to provide strength for the bone The functional unit of the cortical bone is the osteon
What is the central canals of each osteon that give space for blood vessels and nerves? WHat is the name of the canals that connect the osteons by joining between each of the central canals of the osteon and connect the osteons to the periosetum?
The haversion canals are the central canal of each of the osteon The Volkmann’s canal (perforating canal) connect Haversion canals to one another and connect to the periosteum
The trabecular bone is the vertebral body core What is its functional unit?
its functional unit is its trabeculae which arises from the interconnected, open porous network
What is the porous trabeculae filled with? How does the trabecular bone get its blood supply? What is the main function of the trabecular bone?
The porous trabeculae is filled with blood vessels and bone marrow The trabecular bone does not have haversion canals and therefore gets its blood supply via diffusion form bone marrow The main function of trabecular bone is to transfer mechanical forces
- State whether the points listed describe cortical or trabecular bone
- * More surface area
- * Lacks haversion canals
- * Compact
- * Haversions systems
- * Denser
- * Core
- * Surrounding shell
- * Heavy
- * Provides strength
- * Transfers forces
- * Lighter bone
- * Porous 3D network
Cortical bone - compact, haversion systems, denser, surrounding shell, heavy, provides strength
Trabecular bone - more surface area, lacks haversion canals, core, transfers forces, lighter bone, porous 3D network
What type of force does the weight of the body produce on the vertebral column? Which regions of the vertebral column are under most stress?
The weight of the body produces an axial compression force on the vertebral column The thoracolumbar and lower lumbar regions are under the most stress - hence they have the largest vertebral bodies
MOVEMENT AND LOADING OF THE VERTEBRAE How does anterior flexion of the trunk change the way forces act on the vertebral body?
Anterior flexion of the trunk shifts the centre of gravity anteriorly causing shearing forces to act on the vertebrae
How is the anteriorly flexed position of the vertebral column maintained and what does this mean for the forces acting on the vertebrae?
The anteriorly flexed position of the vertebral column is maintained by the erector spinae muscles group eccentrically contracting to counteract and stabilise the flexion movement By doing so, the erector spinae exert a compressive force on the vertebrae
What does Wolff’s law state?
Wolff’s law states that the external shape and internal architecture of bone are determined by the external stresses acting on the bone - meaning a bone grows or remodels in response to the stresses placed on it
How does the remodelling of bone occur? (talk about primary/principle adaptive changes and secondary changes)
The internal architecture of the bone will undergo primary/principle adaptive changes along stress lines before the external shape of the cortical bone will undergo secondary changes Finally the bone becomes stronger and more dense
In areas of stress, trabecular bone reacts in what way?
In areas with stress, trabecular bone becomes more dense and thicker making it a closer, more uniform trabeculae These areas of stress usually cause trabecular patterns to form as a direct function of the stress
The trabecular patterns that form due to areas of stress in bone are known as trabecular systems What is the primary trabecular system in the vertebral body?
The primary trabecular system in the vertebral body is the vertical system
Where is the vertical trabecular system not found in the vertebral column? What is the vertical system composed of?
The vertical system is found throughout the vertebral column with the exception of the IV discs Composed of cylindrical struts of trabecular bone in a vertical arrangement in the central zone of the vertebral body
What is the function of the vertical trabecular system?
This system functions to resist axial compression for weight bearing as well as resisting shocks and jars perpendicular to the vertebral column
What are the secondary systems?
The superior and inferior oblique systems - on each side of the vertebral body and the horizontal system
How many oblique systems are there and where do they run?
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What do the oblique systems resist? Where are the oblique systems absent in the vertebral body? What do horizontal systems resist?
The oblique systems along with the vertical systems resist bending and shear The oblique systems are absent in the anterior vertebral body so this region only has vertical systems and is more prone to fracture
The horizontal system resists muscular tension produced to counteract movements
Which of the trabecular systems has the most resistance to atrophy?
The primary system - the vertical trabecular system - has the most resistance to atrophy out of the trabecular systems
The vertebral body is made up of a shell of cortical bone with an inner core of cancellous bone. What are the advantages of this? (three main points)
* A solid block of cortical bone would be more likely to fracture when forces are applied * Without the addition of cancellous bone, the cortical bone would be a hollow shell which would also be more likely to collapse * The cancellous bone forms trabeculae which acts as the internal architecture of the bone meaning tension is held both vertically and horziontally
The strength of a vertebral body is dependent on four factors. What are these four factors?
The four factors are * the bone mass, * the trabeculae architecture, * the size of the vertebral body and * the thickness of the cortical ring.
Where in the vertebral column is the largest cortical thickness? Where is there a dramatic decrease in thickness? State the values of the cortical thickness if possible
The vertebral column cortical thickness is greatest in the lumbar spine (290nanometres) closely followed by the cervical spine (285 nanometres) There is a dramatic decrease in cortical thickness in the thoracic spine (244 nanometres)
What do the annulus fibrosus and vertebral body cortical shell have in common in regards to thickness?
Both annulus fibrosus and vertebral body cortical shell are thicker anteriorly and thinner posteriorly
How thin is the cartilaginous end plate of the IV disc? How thick is the actual IV disc?
The cartilaginous end plate is approximately 1mm thick The IV disc is approx 7-10mm thick
Where does the end plate tend to be thinnest? What are the components of the end plate?
The end plate tends to be thinnest in the central region adjacent to the nucleus pulposus The components of the endplate are: Osseous component and hyaline cartilage component as well as a cartilaginous component
What is the function of the cartilaginous end plate? WHat does it prevent the bulging off into the vertebral bone?
It is important in maintain the integrity of the vertebral bodies as well as absorbing hydrostatic pressue that results from mechanical loading of the spine It also prevents the highly hydrated nucleus pulposus from bulging into the adjacent vertebral bone
How does the cartilaginous end plate degenerate?
The cartilaginous end plate degnerates with ageing-calcification
