Motion segment Flashcards
what are the components of the vertebrae?
Vertebral body
vertebral arch
7 processes; 1x spinous process, 2x transverse process, 4x articular process
Vertebral notches; indentations superior and inferior to pedicles
what is not present in the atlas?
no body, no spinous process
cervical vertebrae go from where?
C3-C7
what goes through the cervical vertebrae?
vertebral artery, vein and sympathetic nerve plexus run through the foramen transversarium
the thoracic vertebrae has what in order to articulate with what?
has costal facets for articulation with the ribs
what shape is the lumbar vertebral body?
kidney shaped
between the vertebral bodies is what?
intervertebral discs
the intervertebral discs are what kind of joint?
secondary catilagneous
between the articular processes is what?
zygaphophysial joints
what kind of joint are the zygapophysial joints?
plane synovial
where does the anterior longitudinal ligament run?
from the skull base, to the sacrum
what does the anterior longitudinal ligament limit?
extension
where is the posterior longitudinal ligament?
within the vertebral column on the posterior aspect of the vertebral bodies
where does the posterior longitudinal ligament run?
from C2 to the sacrum
how is the posterior longitudinal ligament attached?
Iv discws and margins of the vertebrae
what does the posterior longitudinal ligament limit?
flexion and prevents posterior herniation of the IV disc
ligament flavum connects what?
the laminae of adjacent vertebrae
what is the ligament flavum made up of and what does it help maintain?
strong elastic fibres and helps maintain curvatures?
what does the ligamentum flavum reinforce and what does it limit?
reinforces the wall of the vertebral canal posteriorly and limits flexion
what is the nuchal ligament?
thickened fibroelastic tissue that runs from external occipital protuberance, and the posterior border of the foramen magnum to spinous processes C1-7.
what is the nuchal ligament continuous with and limits what?
supraspinous ligament and limits flexion
the interspinous ligament connects what?
adjacent spinous processes that are thin, weak and membranous
the suprapspinous ligament connects what?
the tips of spinous processes from C7 to sacrum and are cord-like
the intratransverse ligaments connects what?
adjacent transverse provesses
In the cervical region how are the fibres?
scattered
in the thoracic region how are the fibres?
more fibrous
in the lumabr region how are the fibres?
more membranous
roles and responsibilities of the cervical spine?
Supporting the head.
roles and responsibilities of the thoracic vertebrae?
Anchor the rib cage
Less mobile than the neck
roles and responsibilities of the lumbar vertebrae?
Carries the majority of the body weight
More range of motion than Thoracic vertebrae
roles and responsibilities of the sacral spine and coccyx?
Integral to walking, standing and sitting
what do the cervical spine allow?
Allows head flexibility (rotation, flexion/extension, abduction/adduction)
what do the thoracic vertebrae allow?
Limited flexion and extension, some abduction/adduction and reduced axial rotation
what do the lumbar vertebrae allow?
Enables flexion/extension but limits rotation
discuss a study of the stability of the lumbar spine
a study in mechanical engineering explains that the high compressive forces of the spine and adaptations due to the forces. Mechanical stability is maintained by muscle tone. Vertical loading on the spine has to be met with decreased relative lumbar lordosis. A small flexion of the lumbar spine seems to be needed in order to minimise the maximum local muscle stresses at the upper and lower lumbar levels. Such posture adjustment is thought to be automatically performed when a heavy load is carried.
discuss a study on the clinical spinal instability of mechanical stability of the spine and the biomechanical model of the cervical spine
The study resulted in a checklist for the diagnosis of the lumbar spine instability. It uses several elements such as biomechanical parameters, neurologic damage and anticipated loading on the spine.
what is a motion segment?
is a functional unit made up of two adjacent articulating surfaces and the connecting tissues binding them together. E.g 2 vertebrae and an intervertebral disc.
within a motion segment there is what?
2 vertebrae and an IV disc
what is the key component within a IV disc?
nucleolus pulposus
what does the nucleolus pulposus act as?
a ligamentous structure that resists motion and acts as a shock absorber to try prevent shearing forces
what else is key in preventing the range of motion?
facets in the vertebrae
what do the facets do in the vertebrae?
act to protect the spinal cord and stop axial rotation from going further than it should.
what are the two components of a motion segment?
nucleolus pulposus and facets
discuss a paper in relation to Structure and Function of the Lumbar Intervertebral Disk in Health, Aging, and Pathologic Conditions
It explains the tri-joint complex of the IV disc and 2 facet joints that make up the motion segment. It explains that a motion segment is an indication of spinal instability but that it is not in a fixed position and moves around a flexible axis as the body moves.
discuss a paper relatrd to both thoracic and lumbar regions, focusing on biomechanics?
explains that the ribs act in place of the facets in most of the thoracic region. But at the T12-L1 motion segment, there are no ribs and the facets are in a different orientation, causing them to lock during axial rotation. This means that this motion segment has the highest rotatory stiffness of all the motion segments.
role of the IV disc?
Acts as a shock absorber between each vertebrae in the spinal column.
Protect the spinal nerves that run down the middle of the spine
how many IV discs are in the human body?
24
what is the IV discs made out of?
fibrocartilaginous material
what are the 3 parts of the IV disc?
nucleus pulposus
annulus fibrosus
vertebral end plate
all of which are composed of water and collagen
what is the annulus fibrosus made out of?
a strong material with a jelly-like substance known as mucoprotein gel also known as the nucleus pulposus on the inside
as the spine receives pressure what happens to the annulus fibrosus?
the gel moves inside the annulus fibrosus and redistributes itself to absorb the impact of the pressure. The mucoprotein gel loses moisture as a person ages and the spine is able to absorb less shock.
what happens to the outer layer of annulus fibrosus?
deteriorates with age and can begin to rip, and this causes chronic back pain for some people.
how are the fibres orientated in the annulus fibrosus?
orientated in a diagonal but perpendicular ‘criss-cross’ pattern.
what is the IV disc dervied from?
Derived from embryonic structures called the sclerotome and notochord
when does the notochord develop?
Notochord development occurs before vertebrate development
during development and at birth the IV discs have what?
have some vascular supply to the cartilage endplates and also to the annulus fibrosus. These quickly deteriorate leaving almost no direct blood supply in healthy adults.
name some genes involved with the development of the IV disc and what they do?
During development, cells of the notochord release sonic hedgehog (SHH) and noggin (NOG) which facilitate segmentation of the somites into dermatome, myotome, and sclerotome. The sclerotome, in turn, governed by SOX9, PAX1, and HOX family transcription factors, releases bone morphogenetic proteins (BMPs) and transforming growth factor-β (TGF-β) which direct matrix development within the notochord.
what is pre-stress?
IVD is constantly under pressure even in its unloaded state
what is the value of pre-stress
10 N/cm2, 1kg/cm2
why does pre-stress occur?
due to the forces of the tensile resistance by the ligaments, namely ALL, PLL, LF and others, opposing the compressive resistance of the IVD.
what keeps the IVD in a loaded position?
pre-stress
when a load is transmitted on the spine what occurs?
this load is transmitted by the nucleus pulposus in a hydrostatic manner, the load is transmitted evenly through the nucleus pulposus.
When an asymmetrical force, i.e. one that is not acting down the central vertical axis of the IVD, is applied what occurs?
it exerts a rotational force on the disc, as seen in the diagram. As a result, the nucleus pulposus moves away from the load. This causes an increase in the tensile forces of the annulus fibrosus opposite to the load. As a result, there is an opposing moment generated by the tensile strength of the annulus fibrosus, both on the same side, as well as the opposite side of the load. Naturally, the tensile force on the opposite side is larger.
when an axial rotation is applied what occurs?
the fibres orientated in the direction of the rotation are shortened and therefore relaxed, whereas the fibres orientated in the opposite direction are lengthened and therefore under more stress. However this is not the end of the story. The nucleus pulposus is naturally compressed and exerts a resistant compressive force on the annulus fibrosus, similar to the load scenarios described earlier. This causes all fibres, even the ones that were relaxed, to be put under tensile stress, allowing the IVD to limit further rotation.
what does the IVD exhibit?
viscoelasticity
The two viscoelastic properties of the IVD are what?
creep, hysteresis
what is creep?
is the state in which a constant load on the IVD will cause it to slowly deform over time, as opposed to an instant or relatively fast deformation.
what is hysteria?
is how a repetitive loading and unloading on the IVD will gradually cause a change in its elastic properties. Much like how an elastic band, if stretched and unstretched enough times, will start to become ‘loose’
what is spondylosis?
degeneration of the IVD.
how is spondylosis developed?
The cause is multifactorial, that is, it can be due to vessel changes, enzyme dysregulation, disease. also occurs with increasing age, however the literature is undecided as to whether or not age is a factor, or whether age-related disc degeneration is a completely natural and non-pathogenic occurance.
what happens to the micro-structure causes what in the IVD in spondylosis?
cause it to lose some of its important biomechanical properties. The nucleus pulposus, mentioned just now for its unique hydrostatic properties, becomes fibrous and unable to distribute load uniformly. The annulus fibrosus starts to weaken and tear. Similarly, the cartilage end plates become thin and weak. Remember that these are already less able to withstand shear stress compared to the annular fibres. Unsurprisingly, one may start to notice tears occuring between the annulus and the end-plate.
As the IVD loses its weight-bearing properties, the load transmitted through other attachments of the spine naturally does what?
increases, This means that the zygapophysial joints bear the brunt, accelerating OA changes.
what could these changes in the IVD in spondylosis change?
is a prolapse, or herniation of the IVD. This occurs when a tear in the annular fibres becomes large enough that part of the nucleus pulposus inside manages to escape the confines and enter into other spaces. Most commonly, it emerges somewhat laterally, hitting an exiting spinal nerve. This is known as a peripheral prolapse and causes the following symptoms. Radiculopathy, which is pain down a dermatome, and myelopathy, which is pain down a myotome. This is understandable as spinal nerves have been described to supply sensory and motor area along dermatomes and myotomes.
what is spondylolysis?
a condition in which the pars interarticularis, that is the part of bone in between the superior and inferior articular facets of the vertebra, fractures, leading to weakness of the bone to resist forces.
how does spondylolysis occur?
commonly due to repetitive flexion and extension.
what happens in spondylolysis?
one vertebra slips over another due to excessive shear forces which are unbearable by the IVD. The vertebra may be intact or it may fracture and slip. The latter case may be seen in cases where spondylolysis precedes and causes weakness in the motion segment leading to the slippage.
in what population does spondylolysis occur?
It occurs in two distinct age groups, adolescents and the elderly population.
