Intervertebral Discs Flashcards
How many intervertebral discs are in the human body?
23
Each intervertebral disc is given a numeric name relative to which segment?
The segment above
Intervertebral discs constitute what percentage of the entire height of the vertebral column?
20-33%
What are the three parts of the intervertebral disc?
Nucleus pulposus
Annulus fibrosus
Cartilaginous end plates
What makes up the disc to vertebral body ratio?
Height of the IVD compared to the height of the vertebral body
What amount of a disc to vertebral body ratio means there is greater spinal segmental mobility?
Greater ratio
In what area of the spine is the disc to vertebral body ratio greatest? Least? In between?
Greatest = Cervical spine (2:5)
Least = Thoracic spine (1:5)
In Between = Lumbar spine (1:3)
Based on disc to vertebral body ratios, where in the spine do we see the most mobility? Least?
Cervical spine = most
Thoracic spine = least
Where is the nucleus pulposus located in the IVD?
Centrally
What makes up the nucleus pulposus?
Mucoprotein gel with fine fibrous strands
What makes up 70-90% of the nucleus pulposus?
Water
When do we see the most water composition of the nucleus pulposus?
At birth (90%)
When do we see 80% water content of the nucleus pulposus? 70%?
80% = age 20 70% = at old age
Do larger or smaller discs have more capacity to change size? By what mechanism do they accomplish this change?
Bigger discs; creep
What are the differences between cervical and lumbar nuclei of the IVD?
Lumbar - fill 30-50% of the total disc area in cross-section, more posterior than central
Cervical - less defined discs
At what locations is the cervical annulus minimal?
Minimal on lateral borders with thin strip in back
What makes up the annulus fibrosus?
Fibrous tissue in concentric laminated bands
What is the arrangement style of the annulus fibrosis?
Same direction within a band, opposite directions in any two adjacent bands
What angle measurement is formed by the concentric, laminated bands that cross each other obliquely in the annulus fibrosus?
30 degrees to the vertebral body
To where are annular fibers firmly attached?
Cartilaginous endplates in the inner zone
How do peripheral zone annular fibers attach to the vertebral body?
Sharpey’s fibers
What is unique about the attachment involving Sharpey’s fibers?
Stronger than other forms of attachment
What two ligaments reinforce the annular attachments of the IVD?
Anterior and posterior longitudinal ligaments
In which direction does the posterior longitudinal ligament narrow along its path?
Narrows from cervicals to lumbars (descending)
About how much of the central portion of the lower lumbar discs are covered by the posterior longitudinal ligament?
About 50%
What is the weakest area of the annulus and therefore the area most prone to injury? **
Posterolateral aspect
Where in the spine is the most common location for a disc herniation?
Lumbar spine
What are the three functions of the cartilaginous end plate?
Anchor for fibers of the nucleus and annulus
Prevent vertebral bodies from pressure atrophy
Maintain nuclear and annular borders
What part of the cartilaginous end plate is fairly impermeable?
Outer portion
Where does diffusion of nutrients occur in the cartilaginous end plate?
Central portion
What supplies the nucleus pulposus with most or all of its nutrition?
Cartilaginous end plate
Are there any blood vessels that go directly to the IVD?
NO
How do the annular fibers achieve their blood supply?
From adjacent soft tissues
How does the nucleus pulposus achieve its blood supply?
From vertebral bodies
From where can nutrients diffuse into the IVD?
Cartilaginous end plate
When is an IVD considered avascular and aneural?
When healthy
After damage, is the IVD able to self repair easily after the rapid degeneration that occurs?
No - limited self repair
When do IVDs become increasingly vascularized and innervated by sensory nerve fibers?
During disc degeneration and osteoarthritis
What changes occur to the IVD overnight?
Decreased hydrostatic pressure Increased osmotic pressure Increased fluid volume in disc Disc expansion ** INCREASED RESISTANCE TO FORCES = RESULT **
What changes occur to the IVD during the daytime?
Fluid exits the disc
Disc space narrows
Decreased ligament tension
Increased range of motion
How much of the IVD space is lost in seated height?
20 mm
During the day, lumbar flexion can increase by what pecentage?
Up to 50%
Is the IVD viscous or elastic?
Trick question: it’s viscoelastic :)
Compression of what area of the IVD results in tension of the annular fibers?
Nucleus pulposus
What is the result of flexion of the nucleus pulposus?
Compression of the anterior disc and tension on the posterior disc
What chemical change and appearance is seen of the IVD due to age and exposure to biomechanical stresses?
Becomes more fibrous
When flexibility is diminished due to the IVD becoming more fibrous overtime, where is the pressure on the IVD then exerted?
On the annulus and peripheral areas of the end plate
Do all viscoelastic structures exhibit hysteresis?
Yes
What three things make the level of hysteresis vary within a tissue?
Age of the disc
Spinal level involved
Repetitive load
What is the difference of hysteresis in young people vs old people?
Large with very young people and smallest in middle-aged people
At what level of the spine do we see less hysteresis?
Lower thoracic and upper lumbar region
How does hysteresis changes due to repetitive load?
Decreases when successively loaded
What kind of forces are resisted by the nucleus pulposus?
Compressive
How are compressive forces resisted by the nucleus pulposus?
Pushing out against annular fibers
What kind of forces are resisted by annular fibers?
Tensile forces
Gravity and muscle co-contraction are examples of what kind of loads imposed onto the IVD?
Compressive
Flexion, extension, and lateral bending are examples of what kinds of stresses imposed onto the IVD?
Both compressive loads and tensile stresses
What kind of stress occurs on the IVD during axial rotation of the torso with respect to the pelvis?
Shear stress
Is the IVD more susceptible to failure in the area of the forces of tension or compression?
Tension
In what area of the IVD does mechanical failure following compression occur first?
Cartilaginous end plate (nuclear migration occurs)
What physical change is the result of the failure of the cartilaginous end plate and nuclear migration of the IVD?
Schmorl’s node
What is the damaged result from compressive loads in flexion of the IVD?
Anterior collapse of the end plate or vertebral body
Compressive loads in extension are transmitted through what areas?
Facets
Compressive loads in extension result in what type of injury?
Capsular injuries
What is the damaged result from compressive loads applied with torque around the long axis?
Circumferential tears in the annular fibers of the IVD
What provides 90% of the resistance to torque of a motion segment?
Intervertebral discs
What provides the MAJORITY of the torsional resistance?
Annulus
What protects the annulus from being strained by axial rotation in torsion?
Zygapophyseal joints
By what age are 97% of all lumbar discs degenerated?
Age 50
What segments are known to be the most degenerated segments?
L3-L4, L4-L5, and L5-S1
What are the four stages/types of disc herniation?
1 Nuclear herniation
2 Bulge/Prolapse
3 Extrusion
4 Sequestration
In what stage of disc herniation does the nucleus pulposus begin to migrate outward through the defects of the inner annulus but stays within the confines of the IVD?
Nuclear herniation
In what stage of disc herniation does the nucleus pulposus continue to migrate outside the confines of the IVD but NO rupture of the outermost annular fibers occurs?
Bulge/Prolapse
In what stage of disc herniation do the outer annular fibers tear and the contents of the nucleus pulposus move into the epidural space?
Extrusion
In what stage of disc herniation do the discal fragments break loose from the IVD and float freely in the cerebrospinal fluid?
Sequestration
Disc herniation is associated with repeated loading but also what forms of extreme deviated posture?
Full flexion or lateral bending
Is a disc herniation a contraindication to adjust?
NO NO NO NO
What is an example of an additional form of treatment that could help with a disc herniation?
Axial traction
What is the name of the stretching exercising used for treatment of herniated discs?
McKenzie Extension
Can intervertebral discs heal?
YES (takes time)
What kinds of physical activity can we recommend to a patient suffering from a disc herniation?
Low-impact activities like walking/hiking, swimming, elliptical trainer, core muscle strengthening