V.C - C - Motion segement (structure & function), IV disc (forces & moments applied), IV disc pathology & basic anatomy

Question 1

Components of a vertebrae * Vertebral body * Vertebral arch * 7 processes * Vertebral notches What is the adult vertebral body derived from?

Answer 1

The adult vertebral body is derived from the juvenile centrum and the boutons of the pedicles (the boutons of the pedicles are the anterior part of the neural arches)

Question 2

Components of a vertebrae * Vertebral body * Vertebral arch * 7 processes * Vertebral notches What forms the vertebral arches? What are the 7 processes? Where are the vertebral notches?

Answer 2

The vertebral arches are formed by the pedicles and laminae

The 7 processes are:

• Spinous
• Transverse x2
• Superior articular x2
• Inferior articular x2

The vertebral notches are indentations superior and inferior to the pedicles

Question 3

What do the vertebral notches join to form?

Answer 3

The superior vertebral notch aligns with the inferior vertebral notch of the vertebra above forming the intervertebral foramen

Question 4

What makes the C1 vertebrae atypical? What does it articulate with superiorly?

Answer 4

The C1 vertebrae has no spinous or transverse processes Instead it has an anterior and posterior vertebral arch, each with a tubercle Superiroly, the C1 vertebrae articular surfaces articulate with the occipital condyles

Question 5

What is C1 also known as? What is the ligament that holds the dens in place known as? What is the facet on the anterior vertebral arch for?

Answer 5

C1 is also known as the atlas The ligament that holds the dens in place is the transverse ligament of atlas The facet on the anterior vertebral arch is for the insertion of the dens - known as the facet for dens

Question 6

What is C2 also known as? What is the dens? How does the atlas rotate on the axis?

Answer 6

C2 is also known as the axis The dens is upward projection from the body of the axis The transverse ligament of the atlas holds the dens in place allowing the atlas to rotate on the superior articular facets of the axis - axial rotation of the neck

Question 7

What is the difference between the cervical vertebrae spinous process and the the thoracic and lumbar?

Answer 7

The cervical spinous process from C2-C7 are bifid The thoracic and lumbar spinous processes do not split

Question 8

Which cervical vertebrae have a ucinate process ? What is the purpose of the ucinate process and what do they look like?

Answer 8

Cervical vertebrae 3-7 have ucinate processes

These are smooth hook shaped edges of the vertebral body which limit lateral flexion of the cervical vertebral column

Question 9

What is special about the cervical vertebrae transverse processes?

Answer 9

The cervical vertebrae transverse processes have anterior and posterior tubercles serving as a site of muscle attachment with a groove for the spinal nerve running between them

The transverse process also have a foramen within known as the transverse foramen (foramen transversarium)

Question 10

What runs through the transverse foramen?

Answer 10

The vertebral artery, vein and sympathetic plexus run through the transverse foramen Apart from at C7 where only the vertebral vein and sympathetic plexus run through

Pic shows vertebral artery going anterior to transverse process at C7

Question 11

What do the thoracic vertebrae posses for the articulation of the ribs? What is unique about their superior and inferior articular facets? What is unique about their spinous processes?

Answer 11

The thoracic vertebra posses costal facets for the articulations of the rib (superior and inferior costal facets as well as transverse costal facets) The superior and inferior articular facets are nearly vertical facing posteriorly and anteriorly respectively The spinous processes are long and slopig

Question 12

What shape is the lumbar vertebral bodies? What are the additional process and where are they in the lumbar vertebrae? What are the function of the additional processes? What direction do the articular facets of the lumbar vertebrae face?

Answer 12

The lumbar vertebral bodies are kidney shaped There are accessory processes on transverse processes and mamillary processes on superior articular facets The accessory & mamillary processes serve as a site of muscle attachment Superior articular facets face posteromedially Inferior articular facets face anterolaterally

Question 13

What shape is the sacrum? What are the three crests on the sacrum formed from the fusion of? What shape is the coccyx? How do the cocyx and sacrum articulate?

Answer 13

The sacrum is wedge shaped and fused Median crest is the spinous processes; Intermediate crest is the articular processes; Lateral crest is the transverse processes Coccyx is small and triangular Sacrum and coccyx articulate by the cornua of the sacrum and coccyx

Question 14

Between the vertebral bodies are the IV discs Between articular processes are facet joints What type of join are each of these?

Answer 14

IV discs - secondary cartilaginous joint Facet joint (zygapophyseal joint) - synovial plane joint

Question 15

Ligaments of the vertebral column * Anterior longitudinal ligament * Posterior longitudinal ligament * Ligamentum flavum * Nuchal ligament * Supraspinous ligament * Interspinous ligament * Intertransverse ligament Discuss the anterior and posterior longitudinal ligaments

Answer 15

Anterior longitudinal ligament - 3 layers of dense collagen fibres running on the anterolateral surface of the vertebral bodies from skull to sacrum, superficial fibres span multiple vertebral segments and deep fibres bind adjacent vertebrae together, limits extension of the vertebral column Posterior longitudinal ligament - runs within vertebral canal on the posterior aspect of the vertebral bodies from C2 to sacrum and attaches to IV discs and margins of the vertebrae, prevents posterior herniation of IV disc and limits flexion

Question 16

Ligaments of the vertebral column Discuss the ligamentum flavum and nuchal ligament

Answer 16

Ligamentum flavum - attaches adjacent laminae of vertebrae together, it is made up of strong elastic fibres and helps maintain curvatures as well as reinforcing the vertebral canal posteriorly and limiting flexion of the vertebral column

Nuchal ligament - thickened fibroelastic tissue running from the external occipital protuberance and posterior border of the foramen magnum to the spinous process of C7 and is continuous with the supraspinous ligament - site of muscle attachment and limites flexion of the head and neck

Question 17

Ligaments of the vertebral column Discuss the supraspinous, interspinous and intertransverse ligaments

Answer 17

Supraspinous ligament - connects tips of spinous processes from C7 to sacrum and is a tough cord like structure

Interspinous ligament - connects the spinous processes from skull (posterior border of foramen magnum to posterior arch of atlas) to sacrum and is weak, thin and membranous

Intertranvserse ligament - connects the transverse processes of adjacent vertebrae and limits flexion and lateral flexion, * Scattered in cervical region, fibrous in thoracic region and membranous in lumbar region

Question 18

The roles of the joints in the vertebral column differ slightly depending on each vertebral region. Basic roles of the vertebral column are protection of the spinal cord and facilitating the flow of blood to the brain. What is the main role of the cervical spine and what movements does it allow for?

Answer 18

Cervical spine supports the head * Allows for flexion/extension of the head and neck * Lateral flexion of the head neck and * Rotation of the neck

Question 19

What does the thoracic spine anchor and what movements does it allow for?

Answer 19

The thoracic spine achors the rib cage Allows for flexion and extension, some lateral flexion but limited rotation

Question 20

What part of the vertebral column carries most of the body weight? What movements does it allow for?

Answer 20

The lumbar region carries most of the body weight It allows for a greater degree of flexion and extension than in the thoracic vertebrae however limits rotation

Question 21

What are the sacrum and coccyx integral for?

Answer 21

Integral for sitting, standing and walking

Question 22

What is a motion segment?

Answer 22

The motion segement is a functional unit made up of 2 adjacent articular surfaces and the connecting tissues binding them together in simpler terms it is the 2 adjacent vertebrae and the intervertebral disc between the two as well as all adjoining ligaments

Question 23

Motions available by the vertebral column are flexion, extension, lateral flexion and rotation. The individual components that make these motions occur is the motion segment. Two key components of the motion segement are the nucleus pulposus and the facets of the vertebrae How are these components important for the motion segment?

Answer 23

The nucleus pulposus is fundamental for shock absorption to prevent shearing forces and behaves as a ligamentous structure resisting motion The facets of the vertebrae limit the range of movement (axial rotation) possible to protect the spinal cord

Question 24

As stated, the motion segment is the individual components that make motions at the vertebral column occur What is the amount of motion and the direction of the motion occurring due to?

Answer 24

The amount of motion occurring is due to the size of the adjacent vertebral discs and the direction of the motion occurring is due to the orientation of the articular facets

Question 25

As the motion segment is the functional unit made up of 2 adjacent articular surfaces and the connecting tissues binding them together, it can sometimes be described as a tri-joint complex What are these three joints which make up the motion segment?

Answer 25

These three joint are the IV disc and the 2 facet joints

Question 26

In the thoracic region, the facets offer no rotational restriction between the 2 vertebrae. What offers the rotational restriction here instead?

Answer 26

The rotational restriction in the thoracic region is instead provided by the ribs

Question 27

Where is the area of highest rotational stiffness of all the motion segments and why is this?

Answer 27

The area of highest rotational stiffness is at the T12-L1 motion segment This is due to the facets being ina different orientation and therefore causing them to lock during axial rotation (thoracic superior and inferior articular facets face posteriorly and anteriorly respectively) (lumbar superior and inferior articular facets face posteromedially and anterolaterally respectively)

Question 28

What is the largest asvascular structure in the human body?

Answer 28

This would be the intervertebral disc

Question 29

How many IV discs are there in the human body? What are the main functions of the intervertebral discs?

Answer 29

There are 24 IV discs in the human body The main functions are to acts as shock absorbers, between each vertebrae, protect the spinal nerves that run down the middle of the vertebral spinal cord and to limit to resist the motion

Question 30

What are the three parts of the IV disc and what are they composed off?

Answer 30

The three parts are the * The annulus fibrosus * The nucleus pulposus * The vertebral end plate (x2) They are composed off water and collagen

Question 31

What is the gelatinous nuceous pulposus also known as? What happens to this gel as the spine recieves pressure?

Answer 31

The gelatinous nucleus pulposus is also known as a mucoprotein gel As the spine receives pressure, the gel moves inside the annulus fibrosus and redistributes itself to absorb the impact of the pressure

Question 32

What happens to the annulus fibrosus and the nucleus pulposus with age?

Answer 32

The nucleus pulposus loses moisture as a person ages and is therefore is able to absorb less shock The annulus fibrosus deteriorates with age and is therefore more likely to rip which can cause chronic back pain in some people

Question 33

How are the majority of fibres in the annulus fibrosus orientated?

Answer 33

The majority of fibres are orientated in a diagonal yet perpendicular ‘criss-cross’ pattern which helps with resisting tensile load

Question 34

What is the IV disc derived from?

Answer 34

The IV disc is dervided from the sclerotome and the notochord

Question 35

What is the notochord the precursor to? What is the sclerotome the precursor to?

Answer 35

The notochord arises from the mesoderm and is the precursor to the nucleus pulposus of the IV disc The sclerotome forms the vertebral body and contributes to the IV disc

Question 36

During development and at birth, the intervertebral discs have some vascular supply to the cartilage endplates and also to the annulus fibrosus What happens to this blood supply?

Answer 36

This blood supply quickly deteriorates leaving almost no direct blood supply in healthy adults - remember IV disc is the largest avascular tissue in the body

Question 37

Many genes are involved in the development process of the intervertebral discs The mesoderm on either side of the neural tube is known as the paraxial mesoderm which segments into blocks known as the somites. The somite can be split into sclerotomes, myotomes and dermatomes by the action of the notochord What does the notochord release to facilitate segmentation of the somite into sclerotome, myotome and dermatome?

Answer 37

The notochord releases sonic hedgehog protein (SHH) and noggin protein (NOG) which facilitate segmentation of the somite into the slcerotome, myotome and dermatome

Question 38

In turn to the notochord releasing SHH and NOG, the sclerotome, governed by three transcription factors will release proteins to direct matrix development within the notochord What are the three transcription factors governing the sclerotome?

Answer 38

The transcription factors governing the sclerotome are SOX9, PAX1 and HOX SRY-Box 9- SOX- Regulates somite stem cell differentiation into chondrocytes Paired Box 1 (PAX1)- Chondrogenesis of sclerotome cells Homeodomain protein (HOX)- Patterning of vertebrae

Question 39

What are the proteins released from the sclerotome known as?

Answer 39

• Transforming growth factor-B (TGFB)
• Bone morphogenic protein (BMP)
• Transforming Growth Factor-β (TGFB)- vertebral body formation
• Bone morphogenetic protein (BMP) family- In the presence of SHH promotes chondrogenesis of sclerotome-derived disc progenitors.

Question 40

State how the notochord promotes segmentation of the somite State what the sclerotome is governed by and what it releases to direct matrix development within the notochord

Answer 40

Notochord releases sonic hedgehog (SHH) & noggin (NOG) protein which facilitate segmentation of the somite into sclerotome, myotome and dermatome

In turn the sclerotome, governed by SOX9, PAX1 and HOX transcription factors releases BMP and TGFB to direct matrix development within the notochord

Question 41

Firstly, in order to understand how the IVD can come to be injured, let us look at what happens to the IVD in a normal loading situation. As with all things biomechanical in the body, we break it down into forces and moments. What is the differences between forces and moments?

Answer 41

Both forces and moments are vectors as they have a direction and magnitude Although forces are linear and moments are rotational

Question 42

We have moments and forces acting on the IV disc Let us focus on forces first (linear) It is important to note that the IVD (intervertebral disc) is constantly under pressure even in its unloaded state What is this pressure known as?

Answer 42

The constant pressure is known as the intrinsic pressure or the pre-stress state

Question 43

What is the value of the pre-stress pressure (intrinsic pressure) on the IV disc in its unloaded state?

Answer 43

The value is reported to be 10N/cm² or 1kg/cm²

Question 44

What does the pre-stress acting on the IVD arise due to?

Answer 44

This arises due to the tensile resistance by the ligaments - mainly ALL, PLL and ligamentum flavum - opposing the compressive resistance of the IVD The ligaments try to hold the joint together whereas the IVD is resisting the joint becoming fused

Question 45

It is the pre-stress which keeps the IVD in a loaded position. In fact, the human spine can stay in an upright position all on its own if you just have the bones, ligaments and IVDs! No muscle is needed to keep it erect in anatomical position! What is the difference between a compressive and a tensile force?

Answer 45

Compressive forces result in shortening - due to a force which causes squeezing (compression) Tensile forces result in elongation - due to a force which causes stretching usually

Question 46

When a load, is placed on the spine (pretend it’s bodyweight), this load is transmitted by the nucleus pulposus in a hydrostatic manner. What does this mean?

Answer 46

The nucleus pulposus transmitts the load in a hydrostatic manner meaning the load is spread uniformyl through the nucleus pulpsous and contained by the vertebral body and annulus fibrosus - this means the load is not putting direct pressure in the one place

Question 47

The nucleus pulposus experiences compessive forces and the annulus fibrosus wil contain the load by stretching, a tensile load What is the max force able to be experienced by both the annulus fibrosus and the nucleus pulposus?

Answer 47

The annulus fibrosus can experience tensile loads up to 5x its original

The nucleus pulposus can experience compressive loads up to 1.5x its original

Question 48

Now that we’ve looked at axial load, let us look at the effect of rotational forces and torque on the IVD. When an asymmetrical force, i.e. one that is not acting down the central vertical axis of the IVD, is applied, it exerts a rotational force on the disc What is a rotational force known as? Where does the nucelus pulposus move as an asymmetrical load is applied?

Answer 48

The rotational force is known as a moment The nucleus pulposus moves in an opposite direction from the load applied

Question 49

What does the movement of the nucleus pulposus cause?

Answer 49

The movement of the nucleus pulposus cause an increase in the tensile strengh of the annulus fibrosus opposite to the load

Question 50

As a result of the asymmetrical load being applied, nucelus pulposing oving away fro the load and increasing the tensile strength in the annulus fibrosis opposite to the load, where is the greatest opposing moment generated by the tensile strength of the annulus fibrosus?

Answer 50

A moment is generated by the tensile strength of the annulus fibrosus on both the same side and opposite side. Naturally however, the tensile force on the opposite side will be larger

Question 51

In terms of axial rotation, we have to consider the microstructure of the collagen fibres in the IVD. As pointed out earlier, the majority of the fibres of the annulus fibrosus are orientated in a diagonal but perpendicular ‘criss-cross’ pattern. What happens to the fibres during axial rotation?

Answer 51

During axial rotation, the fibres orientated in the direction of the rotation shorten and relax whereas the fibres which are in the opposite direction are lengthened and therefore under more stress

Question 52

The nucleus pulposus is naturally compressed during axial rotation 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. What does this do to the rotation?

Answer 52

The resistant compressive force exerted on the annulus fibrosus by the nucleus pulposus ensures all annulus fibrosus fibres are now under tensile stress and this further limits axial rotation

Question 53

Is the tensile strength of the vertebral body or the annulus fibrosus greater?

Answer 53

An important point to note is that the annulus fibrosus has greater tensile strength than the vertebral bodies. This has implications for pathology which we will encounter later on.

Question 54

Discussed pre-stress and axial loading in terms of forces on the IVD Discussed asymmetrical loading and axial rotation in terms of moments on the IVD What properties allow the nucleus pulposus to be a uniform load transmitter? What is the role of the vertebral body?

Answer 54

* The nucleus pulposus acts as a uniform load transmitter due to its hydrostatic properties

* The annulus fibrosus acts as an opposing resistor of the nucleus pulposus thanks to its tensile properties

* The vertebral bodies acts as an endplate and container for the whole process and their relative weakness for tensile strength compared to the annulus fibrosus has been noted

Question 55

Before we move onto the pathology, some important properties to note about the IVD It exhibits what is known as viscoelasticity. This basically combines the words ‘viscosity’ and ‘elasticity’. A viscous material resists internal flow much like a cake batter before you bake it. Elastic materials exert resistant forces when stretched and can accommodate a deformation to a greater extent than non-elastic materials. What are the two viscoelastic properties of the IVD?

Answer 55

The two viscoelastic properties are creep and hysteresis

Question 56

What is creep? Give an example of when creep is reversible

Answer 56

Creep is the constant load causing the slow deformation of the IVD - due to the IVD elastic nature it can potentially be reversed (for example those who those seated at a desk all day will have a constant load on the IVD causing it to deform and then at night, when lying flat the load has disappeared and the IVD goes back to normal)

Question 57

What is hysteresis? Give an analogy

Answer 57

Hysteresis the repetitive loading and unloading off the IV joint, which will eventually cause a change in the IVD elastic properties Much like an elastic band that it is repeatedly stretched, eventually it will not retain its elasticity

Question 58

Another important property of the IVD, especially when it comes to the lumbar IVD, is that the posterior aspect of the annulus fibrosus is thinner than the anterior. Why is this odd?

Answer 58

This is odd as the posterior aspect of the annulus fibrosus is subject to the most stress, naturally being at the lower end of the vertebrae and therefore experiencing greater loads which makes it a common site of injury

Question 59

Spondylosis is a general term for degenerative arthritic changes of the spine It is a degenerative condition that may worsen as a person grows older. What are the structural changes that happen to the nucleus pulposus, annulus fibrosus and end plate during spondylosis?

Answer 59

The nucleus pulposus becomes more fibrous meaning it cannot uniformly spread the load as it has lost its hydrostatic properties The annulus fibrosus begins to weaken and tear The end plate also becomes very thin and tears One may notice tears between the end plate and annulus fibrosus

Question 60

As the IVD loses its weight-bearing properties, the load transmitted through other attachments of the spine naturally increases. This means that the zygapophysial joints bear the brunt. What can this accelerate?

Answer 60

The increased weight load through the zygapophyseal joint can accelerate facet joint osteoarthritis

Question 61

The first thing that could occur with these changes is a prolapse, or herniation of the IVD. How does the herniation occur? What direction does the herniation occur in and what is it known as?

Answer 61

As the annulus fibrosus becomes weaker, it can tear allowing nucleus pulposus to herniate Usually the herniations occur laterally and are known as peripheral herniations and can impinge on a spinal nerve (causing a radiculopathy (pain in dermatome) or myelopathy ( pain in myotome)) but herniations can rarely occur centrally

Question 62

Spondylolysis is 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. What does it commonly occur due to? Spondylolysis is not IVD pathology but connects to the next IVD pathology

Answer 62

It commonly occurs in adolescents who over train in activities as there is repetitive flexion and extension

Question 63

What is spondylolisthesis? What does it occur due to?

Answer 63

Spondylo - spine Olisthesis - slippage It means slippage of one vertebrae over another due to excessive shearing forces

Question 64

In spondylolisthesis, 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. When may the vertebrae have a fracture and slip?

Answer 64

The vertebrae may have a fracture and slip in cases such as spondylolysis where this pars interarticularis fracture has caused a weakness in the motion segment leading to the slipping. Usually occurs in adolescents or the elderly

Question 65

What are both scans showing?

Answer 65

Left scan is an MRI showing herniation of the L4/5 intervertebral disc - could be due to spondylosis making a herniation more likely Right scan is an xray showing spondylolisthesis of the L5/S1 vertebrae