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Biomechanics > (1) Biomechanics-- IVD > Flashcards

(1) Biomechanics-- IVD Flashcards

1
Q

How many adult IVD are there? What is their numeric name based on?

A

23 discs; name based on segment ABOVE

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2
Q

What does the unique and resilient structure of the disc allow for?

A

function in weight-bearing and motion

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3
Q

What percentage do the discs contribute to of the entire height of the vertebral column?

A

20-33%

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4
Q

What are the three parts of the IVD?

A
  1. Nucleus pulposus
  2. Annulus fibrosus
  3. Cartilaginous end plates
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5
Q

What are we comparing in the Disc to VB Ratio? What does a greater ratio mean?

A

height of IVD compared to height of VB

greater ratio means greater spinal segmental mobility

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6
Q

Describe the IVD and VB ratio in the cervicals, thoracics, and lumbars.

A

Greatest in C spine (2:5)
Least in T spine (1:5)
in b/w in L spine (1:3)

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7
Q

List from most mobile to least mobile of the regions of the spine.

A

Most mobile = cervicals
in b/w = lumbars
least mobile = thoracic

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8
Q

What is the water content of the Nucleus Pulposus?

A

70-90% water content

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9
Q

What is the water content of the Nucleus pulposus at:

  1. birth
  2. age 20
  3. old age
A
  1. birth = 90%
  2. age 20 = 80%
  3. old age = 70%
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10
Q

Do larger or smaller size discs have more capacity to change size? aka creep

A

bigger discs have more capacity to change size (creep)

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11
Q

What do the IVD disc cells make?

A

the “solutes”–> matrix (proteins, proteoglycans, GAGs)

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12
Q

How much of the total disc area in cross-section do the Lumbar nuclei fill? What direction are they more located?

A

fill 30-50% of total disc cross-section

located more POSTERIOR than central

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13
Q

Where is the annulus more minimal in the cervicals? Why?

A

on the lateral borders; and only a thin strip in back

due to uncinate processes reinforcing at lateral border

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14
Q

Describe the make up of the Annulus Fibrosus.

A

Fibrous tissue in concentric laminated bands

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15
Q

What is the orientation of the concentric laminated bands w/in a band and in adjacent bands?

A

SAME direction w/in a band

OPPOSITE directions in any two adjacent bands

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16
Q

At what orientation do the concentric laminated bands appear to cross another? What degree angle does this form to the VB?

A

appear to cross one another obliquely

form angle of ~30 degrees to VB

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17
Q

What do the Annular fibers firmly attach to?

A

the cartilaginous endplates in the inner zone

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18
Q

How do the inner zone annular fibers attach to the endplates? How do the peripheral zone fibers attach to the VB?

A

inner zone–> firmly attached to endplates

peripheral zone –> attach to VB via “Sharpey’s Fibers”-> STRONGER than other attachments

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19
Q

What two ligaments of the spine reinforce the annular fibers?

A

ALL and PLL

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20
Q

Describe the PLL along the spine as it goes from Cervicals to Lumbars.

A

narrows from C –> L, until it covers only ~50% of central portion of lower lumbar discs

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21
Q

What percentage of the lower lumbar discs are covered by the PLL?

A

~50%

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22
Q

What is the WEAKEST area of the annulus? What does this increase the risk of?

A

POSTEROLATERAL ASPECT

area most likely to be injured– like disc herniation

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23
Q

Where is the most likely spot for a DISC HERNIATION in the lumbar spine?

A

posterolateral aspect (b/c that is where annulus is weakest

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24
Q

What is responsible for being an anchor for fibers of the nucleus and annulus, preventing VBs from pressure atrophy, and maintaining nuclear and annular borders?

A

Cartilaginous End plates

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25
Q

Where part of the cartilaginous end plate is fairly impermeable? Where does it get its nutrient from?

A

outer portion is fairly impermeable

gets nutrients from diffusion in central portion

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26
Q

What supplies the nucleus pulposus with most or all of the its nutrition?*

A

cartilaginous end plates

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27
Q

T/F. The disc has blood vessels that go directly to it.

A

FALSE— NO blood vessels go directly to the disc

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28
Q

Where do annular fibers of the disc get blood supply?

A

from adjacent soft tissues

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29
Q

Where does the nucleus pulposus get blood supply from?

A

vertebral bodies

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30
Q

Where does the IVD get its nutrients from?

A

annular fibers–> from adjacent soft tissues
nucleus pulposus–> from VBs

also diffuse into disc from end plate

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31
Q

What type of vascularity and neural tissue does the IVD have?

A

avascular and aneural tissue!!!!

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32
Q

Describe the repair ability of a IVD when it undergoes rapid degeneration.

A

limited self repair

33
Q

What happens to disc during disc degeneration and osteoarthritis?

A

they become increasingly vascularized and innervated by sensory nerve fibers

34
Q

What happens to the disc overnight:

  1. Hydrostatic pressure
  2. osmotic pressure
  3. fluid volume in disc

What overall effect does this have on the disc?*

A
  1. decreases
  2. increases
  3. increases

disc EXPANDS = increased resistance to forces*

35
Q

What happens to the disc during daytime:

  1. fluid of disc
  2. ligment tension
  3. ROM
A
  1. CREEP–> fluid exits the disc and disc space NARROWS
  2. decreases
  3. ROM increases
36
Q

What is the loss in seated height during the daytime due to the disc space narrowing?

A

~20mm

37
Q

What is the percentage that the lumbar flexion ROM increases?*

A

up to 50%

hence why right in the morning if one bends over right away, may hear a “snap”

38
Q

T/F. The IVD is viscoelastic

A

True

39
Q

What makes it difficult to study the disc?

A

due to variation in loading in different sections of the disc

40
Q

What does compression of the nucleus pulposus result in?

A

tension of the annular fibers

41
Q

Where does flexion put compression and tension on the disc?

A

compression on ANTERIOR disc

tension on POSTERIOR disc

42
Q

Where is compression and tension put on the IVD during extension?

A

compression at POSTERIOR disc

tension on ANTERIOR disc

43
Q

Out of compression and tension, which are we more concerned about when it comes to the IVD?

A

more concerned about where tension is placed, b/c the disc can handle compression

44
Q

What happens to the disc as we age in relation to elasticity?

A

with age– exposure to biomechanical stresses, disc becomes more fibrous and flexibility diminishes

45
Q

Will a healthy disc or a disc that has been injured deform more?

A

an injured disc deforms more than a healthy one

46
Q

T/F. All viscoelastic structures exhibit hysteresis.

A

True

hysteresis = the absorption or dissipation of energy by a distorted structure

47
Q

What three things will Hysteresis vary with associated to the IVD?

A
  1. age of disc
  2. Level of disc
  3. Repetitive load on disc
48
Q

Where along the spine do the IVD has less hysteresis? Why does this mean for that area?

A

lower thoracic and upper lumbar region–> therefore cannot load and unload well

49
Q

How will a repetitive load have an impact on Hysteresis for IVDs?

A

hysteresis decreases when successively loaded

50
Q

Compare the impact on a rapidly loaded disc vs one that is slowly loaded.

A

loaded more rapidly–> disc behaves more STIFFLY (deforms less) than when loaded slowly

with rapid loading the IVD is less effective at absorbing shock

51
Q

When loading occurs on the IVD, what type of forces does the nucleus pulposus resists?

What about the Annular fibrosus?

A

nucleus pulposus resists COMPRESSIVE forces

annular fibers resists TENSILE forces (resists being “stretched”)

52
Q

What are the three loads imposed on IVDs?

A
  1. Compressive loads
  2. Tensile Stresses
  3. Shear stresses
53
Q

What causes the Compressive Loads on our IVDs?

A
  • gravity and muscle co-contraction

- flexion, extension, and lateral bending

54
Q

What causes Tensile Stresses on the IVDs?

A
  • flexion, extension, and lateral bending

- traction

55
Q

What causes Shear stresses on the IVDs?

A
  • axial rotation of torso w/ respect to pelvis
  • Anterior posterior
  • Left right
    (translating in a linear direction)
56
Q

Is the disc more susceptible to failure in the area of the forces of tension or compression?

A

more susceptible to failure in the area of the forces of TENSION

57
Q

Where does Mechanical Failure occur first in the spine during compression forces?

A

in the cartilaginous endplates—> leads to nuclear herniation, called “Schmorl’s node”

58
Q

Where will compressive loads in flexion cause collapse of the endplate or VB?

A

anterior collapse

59
Q

Besides Schmorl’s nodes, what is an additional failure that occurs in the spine to withstand compressive forces?

A

compression fractures

60
Q

Go through the steps of what occurs to the VB under compression.

A

disc compresses–> cartilaginous end plates bulge inward–> cortical bone (outside of barrel) is strong–> so cancellous bone compresses–> vertical struts buckle–> transverse bone may fracture (they can heal, maintaining the original structure)

61
Q

Where are compression forces transmitted in the spine during extension? Why type of injuries does this lead to?

A

through the facets–> leading to capsular injuries

62
Q

What can compressive loads on the spine, combined with torque around the long axis (aka ROTATION) produce in the IVD?

A

circumferential tears in the annular fibers of the IVD

63
Q

What two forces will cause an Annular Tear?

A

compression and rotation

64
Q

What percentage of the resistance to torque of a motion segment is provided by IVDs? Of this percentage, what part of the disc provides the majority of resistance?

A

90%

annulus

65
Q

How is our spine usually protected from torsion injuries?

A

due to the zygapophysis joints stopping body from rotating that far

66
Q

What is Biomechanical behavior dependent on?

A

the state of degeneration–> which is dependent upon age of disc

67
Q

By age 50, what percentage of lumbar discs are degenerated to some stage?

A

age 50

68
Q

What are the most degenerated segments?

A

L3-L4
L4-L5
L5-S1

(lumbars)

69
Q

What are the 4 Stages/Types of Disc Herniation?

A
  1. Nuclear Herniation
  2. Bulge/Prolapse
  3. Extrusion
  4. Segquestration
70
Q

Describe how a Nuclear Herniation occurs.

A

nucleus pulposus begins migrating outward through defects of inner annulus

it stays WITHIN confines of IVD

71
Q

Describe a Bulged/Prolapsed disc.

A

additional migration of nucleus pulposus OUTSIDE confines of IVD, but NO rupture of outermost annular fibers

72
Q

Describe an Extrusion of a disc. Why type of symptoms may one have?

A

outer annular fibers TEAR and contents of nucleus pulposus move into epidural space

segment level symptoms–> like dermatome or muscle dysfunction

73
Q

Describe a Sequestration of a disc. What type of symptoms may one have?

A

distal fragments break loose from IVD and float freely in CSF

traveling of symptoms–~2 segments due to fragments floating around

74
Q

What are two things disc herniation are associated with?

A
  1. extreme deviated posture; full flexion or lateral bending

2. repeated loading (hysteresis)–> 20-30 thousand times, fatigue

75
Q

How can sudden disc prolapse occur?

A

sudden compressive loading and lateral bending

76
Q

What are three common characteristics of those who had sudden disc prolapse with sudden compressive loading and lateral bending?

A
  1. 40-49 years old
  2. DDD
  3. lumbar levels of L4/L5 or L5/S1
77
Q

What are some postural habits that increase lumbar spine flexion?

A
  1. crossing legs while sitting (53% flexion)
  2. Squatting down on heels (70-75%)
  3. Lifting light weights from ground (70-100%)
  4. Rapid lunging (100-110%)
78
Q

Can we and should we adjust a patient that has a herniated disc?

A

YES!

  • only a contraindication if patient can’t tolerate it/ Cauda Equina Syndrome
  • safe if we are aware of position putting patient in
79
Q

What are two other options for a patient that has a herniated disc, besides adjusting?

A
  • Axial Traction
    (Traction = takes compressive forces off spine and allows disc to re-fill with water)
  • McKenzie Extension Exercises

Biomechanics (6 decks)

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