Biomechanics of the vertebral body; trabeculae, cortical thickness and end plate Flashcards
C3-C7 are wider where?
transversely than anteroposteriorly
They have a convex inferior surface and concave superiorly due to what?
the unicate process protruding upwards on the lateral borders
what does the atlas lack?
a vertebral body or spinous process
instead of a vertebral body to act as the weight bearing structure what does the atlas have?
lateral masses
in relation to the atlas what is on the lateral masses?
the transverse articular surfaces in which the atlas connects with the cranium via the occipital condyles
what is the strongest of the cervical vertebrae?
axis
what does the axis allow?
pivoting movement of the head due to its unique structure
what are the types of bone making up the lumbar vertebrae and what do they allow?
Outer cortical bone shell
Large section of cancellous bone deep to this.
Cancellous bone allows for dynamic compression where the cortical bone would just fracture if it alone was exposed to this
what are the trabecular systems surrounded by?
compact bone
bone is what?
hard and resilent
what is bone composed of?
65% mineral salts
23% collagen
10% water
2% non-collagen proteins
what is surrounding the bone?
a periosteum outer-layer; fibrous and osteogenic
cortical bone is what?
relatively dense and compact
in vertebrae what does cortical bone form?
a surrounding shell, around the trabecular bone
what is the main role of cortical bone?
provide strength
what does cortical bone contain?
osteon around haversian canals, give space for blood vessels and nerves
what is the functional unit of trabecular bone?
trabeculae
what is trabecular bone?
vertebral body core
trabeculae form what?
interconnected, open porous network
what are the pores filled with in trabecular bone?
bone marrow and blood vessels
what does trabecular bone lack?
haversian canals
where does trabecular bone get its nutrients?
via diffusion from bone marrow
what is the main role of trabecular bone?
transfer mechanical force
characteristics of cortical bone?
harversian systems, denser, compact, surrounding shell, heavy, provide strength
characteristics of trabecular bone?
lacks haversian canals, more surface area, porous (3D network), core, lighten bone, transfer forces
weight of the body produces what?
an axial compressive force on the vertebral column
what percentage of weight is transferred to trabecular bone in the vertebral body?
25%-90%
what vertebrae are under most stress?
thoracocolumbar and lower lumbar region
anterior flexion of the trunk does what to the COG?
shifts the COG forward and creates shearing forces on the vertebrae
to maintain anterior flexion of the trunk what is happening?
erector spinae muscles are acting to counteract and stabilise this movement, in doing so they are exerting a compressive force on the vertebrae
what is wolffs law?
bone function changes cause bone structure modification
limitations of wolffs law?
Fails to account for hormonal activity governing the activity of osteoclasts and osteoblasts in defining bone density
To combine hormonal influences and mechanical forces as stress on bone the Mechanostat theory and Utah Paradigm was formed.
in areas of stress, trabecular bone reacts in what ways?
Areas with most stress develop more dense trabeculae
Thicker trabeculae
Closer more uniform spacing of trabeculae
Along areas of stress trabecular patterns form as a direct function of stress
where is the vertical system found?
the vertebral column with the exception of the IV discs
what is the vertical system composed of?
large cylindrical struts of trabecular bone in vertical arrangement in the central zone of the vertebral body
what is the functional role of the vertical system?
to resist acial compression for weight bearing
what does the vertical system resist?
shocks and jars perpendicular to the vertebral column
the vertical system has the most resistance to what?
atrophy out of the trabecular systems
what are the primary systems?
vertical system
what are the secondary systems?
horizontal and oblique systems
how many oblique systems are there?
4, 2 superior, 2 inferior
what to oblique systems resist?
torsion, they are woven together
oblique systems along with vertical resist what?
bending and shear
horizontal systems resist what?
muscular tension produced to counteract movements
superior oblique runs where?
runs from superior articular process through pedicle to lower surface of the vertebral body
inferior oblique runs where?
runs from inferior articular process through pedicle to upper surface of the vertebral body
oblique systems absent where?
in anterior surface of vertebral body making it more prone to fracture
the vertebral body is made up of what?
a shell of cortical bone with an inner core of cancellous bone
a solid block of cortical bone is likely to what?
to fracture along cleavage planes when dynamic force is applied to it.
without the addition of cancellous bone in the centre the cortical bone would be what?
be a shell which is also likely to collapse when force is applied.
the cancellous bone forms what?
vertical and transverse trabeculae which act as the internal architecture of the bone. They form ‘cross beam’ like structures meaning tension is held both transversely and vertically in the vertebral body.
the strength of a vertebral body is dependent on what 4 factors?
bone mass, the trabeculae architecture, the size of the vertebral body and the thickness of the cortical ring.
which spine has the largest thickness?
lumbar spine (290um)
what is the second largest thickness of spine?
cervical spine (285um)
what thickness is the thoracic spine?
244um
the vertebral bodies cortical shell is thicker where?
anteriorly thicker and thinner posteriorly
is the cartilagenous end plate thick or thin?
very thin; 1mm
how thick is the IVD?
7-10 mm
where is the CEP thinnest?
in the central region adjacent to the nucleus pulposus
what does the CEP contain?
osseous component and a hyaline cartilage and cartilaginous component
what is the function of the CEP?
maintaining the integrity of the vertebral bodies
what does the CEP absorb?
Simultaneously absorbs hydrostatic pressure that results from mechanical loading of the spine
what does the CEP prevent?
Prevent the highly hydrated nucleus from bulging into the adjacent vertebral bone
the CEP degenerates with what?
Degenerates with ageing- calcification