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Vertebral Column > Biomechanics Of The Vertebral Body > Flashcards

Biomechanics Of The Vertebral Body Flashcards

1
Q

What regions of the vertebral body are stressed and unstressed in vertebral Flexion?

A

Large compressive stresses in posterior parts

Centre is pretty unstressed

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2
Q

What stresses are present during vertebral axial loading?

A

Large stresses all over vertebral body:

  • Load is divided
  • Allows vertebra to transmit applied force
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3
Q

What is a shear force?

A

A force acting parallel to a material so as to tend to deform it

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4
Q

What is the shear angle?

A

Angle between deformed body and original position

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5
Q

What stresses result from anterior shear forces on the vertebrae?

A

Large anterior compressive stresses at pedicel bases

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6
Q

What is the reference for basic loads and the resultant vertebral stresses?

A

Smit et al., 1997

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7
Q

What is the typical shape of the cervical vertebral body?

A

Small

Kidney shaped

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8
Q

How does the superior surface of the cervical vertebral bodies appear? (Reference?)

A

Raised laterally
Flat posteriorly
(Palastanga and Soames, 2012)

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9
Q

What is the typical shape of a thoracic vertebral body when viewed superiorly? (Reference?)

A

Heart shaped
Larger than cervical vertebrae
(Palastanga and Soames, 2012)

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10
Q

Why are the superior and inferior surfaces of the lumbar vertebral bodies parallel? (Reference?)

A

The flat surfaces:
- Help withstand longitudinal loading
- Give stability to the intervertebral joints
(Bogduk, 2005)

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11
Q

How does Bogduk (2005) describe the vertebral bodies of the sacrum?

A

Rectangular areas, resembling bodies, embedded in sacrum

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12
Q

Where does the apex of the sacrum lie? (Reference?)

A

Inferiorly

Strandring et al., 2008

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13
Q

What is the internal structure of the vertebral body? (Reference?)

A

Not completely solid
A ‘box’ filled with transverse and oblique ‘struts’
- Struts = Trabeculae

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14
Q

What influences the structure of the trabeculae within vertebral bodies?

A

Basivertebral vein

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15
Q

What fills the spaces between trabeculae within vertebral bodies?

A 
Bone marrow
Blood vessels (arterial and venous)
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16
Q

How do trabeculae affect the structure of the vertebral bodies?

A

Make it lightweight but strong

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17
Q

What is the reference for the trabecular structure of vertebral bodies?

A

Bogduk, 2005

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18
Q

What is the structure of a vertebral endplate? (References?)

A 
Hyaline cartilage:
- Immediately adjacent to IV disc
- Strandring et al., 2008
Osseous component:
- Surrounding hyaline component
- Moore, 2000 and 2006
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19
Q

Why does the endplate calcify as we age?

A

Blood vessels obliterate

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20
Q

What is the sequelae for the IV disc due to endplate calcification? (Reference?)

A

Less nutrients to IV disc via diffusion/osmosis

Palastanga and Soames, 2012

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21
Q

What is the thickness of a vertebral endplate and where are they thinnest?

A

1mm

Thinner in centre

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22
Q

What are the functions of vertebral endplates?

A

Prevent nucleus pulposus bulging into vertebral body
Absorb forces from mechanical loading of spine
Play a role in fluid/nutrient exchange between:
- Vertebral bodies
- Rest of IV disc

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23
Q

Grant et al., (2001) did a study on endplate strength. What were some of the findings?

A

Centre is weakest
Areas in posterior endplate are strongest:
- Lumbar around pedicels
- Sacral (unspecified)
Inferior endplate stronger than superior endplate of each IV disc

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24
Q

What are the limitations of the Grant et al., (2001) study on endplate strength?

A

Focused on lumbar and sacral vertebrae only (L3-S1)

Mean specimen age around 75 years

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25
Q

What are the implications of endplate strengths?

A

Surgical implications:

  • Fixations
  • Implants
26
Q

The trabeculae bone of vertebral bodies is highly porous and anisotropic. What does this mean?

A

It’s physical property has different values when measured, via micro-CT on cross-sections, in different directions

27
Q

Where else is trabecular bone found? (Reference?)

A

Epiphyses of long bones

Oftadeh et al., 2015

28
Q

What do the trabecular systems of vertebral bodies reflect? (Reference?)

A

The stresses they are subject to

Palastanga and Soames, 2012

29
Q

How is the central zone of trabecular bone described?

A 
Large cylinders (walls of lamellar bone)
Vertical in arrangement (around basivertebral veins)
30
Q

How are the trabecular zones lying laterally to the central zone described?

A

Consist of longitudinal and transverse trabeculae
Spaced regularly:
- Directly beneath endplate

31
Q

Why are the superoanterior and inferoanterior zones of trabecular bone the reasons for compression vertebral fractures?

A

Less trabecular bone present = Areas of weakness

Due to oblique systems not reaching the anterior margin of the vertebral body

32
Q

Where is the principal vertical trabecular system found?

A

In all vertebral bodies

33
Q

What are the functions of the principal vertical trabecular system?

A

Sustains body weight

Sustains all shocks perpendicular to vertebral column

34
Q

What is the course of the superior oblique trabecular systems?

A

Run from superior articulate process through pedicle to the lower surface of the vertebral body on the contralateral side

35
Q

What is the course of the inferior oblique trabecular systems?

A

Run from inferior articulate process through pedicle to upper surface of the vertebral body on the contralateral side

36
Q

How many oblique systems are there per vertebral body?

A 
2 superior (one on each side)
2 inferior
37
Q

What are the functions of the oblique trabecular systems?

A

Resist torsion

Resist bending and shear (with vertical system)

38
Q

What trabecular system at the oblique systems continuous with?

A

Continuous posteriorly with trabeculae in spinous process

39
Q

What is the course of the horizontal trabecular systems?

A

Begin in each transverse process

Pass into vertebral body and interest in midline

40
Q

What is the function of the horizontal trabecular system?

A

Resist tension along with accessory systems of transverse and spinous processes:
- Resist muscle pull

41
Q

What is the reference for the trabecular systems of vertebral bodies?

A

Palastanga and Soames, 2012

42
Q

What did Ebraheim et al., (2000) discover when they investigated the trabecular architecture in the sacrum?

A

Sacrum does not bear weight

Trabeculae mostly concentrated in S1 and S2

43
Q

What did Bogduk, (2005) find in regards to Sacral trabeculae?

A

Sacrum and L5 bear similar load

Implies sacrum is large because of its pelvic function and not due to weight bearing

44
Q

What trabecular systems exist in the sacrum?

A

Vertical

Transverse

45
Q

What is the new name for Wolff’s law?

A

Bone functional adaptation

46
Q

How is trabecular bone strength defined? (Reference?)

A

The maximum stress a structure can withstand before failing

Oftadeh et al., 2015

47
Q

What is Wolff’s law?

A

Structural adaptations of bones due to mechanical usage:

- Result in vertebral body architecture optimally suiting site individual needs

48
Q

What stresses contribute to bone functional adaptation? (Reference?)

A 
Compressive
Tensile:
- Lateral shear
- Flexion
- Lateral Flexion
(Smit et al., 1997)
49
Q

What does a lateral x-ray through a pedicle of a lumbar vertebra show?

A

Pedicle are a bony cylinder:

  • Trabeculae run in a fan-shape to each endplate
  • Density of trabecular bone higher here than elsewhere
50
Q

What does the trabecular architecture and vertical orientation of facet joints suggest?

A

Walking determines architecture of lumbar vertebrae

51
Q

What did Smit et al., (1997) find regarding the loading of lumbar vertebrae and the relationship of this to trabecular architecture?

A

They are loaded by:

  • Axial compression (gravity and muscular forces)
  • Compression within facet joints during:
    1. Anterior and lateral shear
    2. Axial torsion (walking)
52
Q

Why do vertebrae need loaded regularly?

A

To prevent bone resorption (bending may not be sufficient)

53
Q

What does Smit et al., (1997) suggest is the order of events that results in the trabecular architecture of lumbar vertebrae?

A
  1. Walking
  2. Rotation of body segments
  3. Axial torsion
  4. Transformed to horizontal shear
  5. Facet joint loading
  6. Trabecular architecture
54
Q

What are the components of both trabecular and cortical bone?

A

Hydroxyapatite
Collagen
Water

55
Q

What component of bone is reduced in trabecular bone and what effects does this have on density and ash fraction?

A

Hydroxyapatite
Reduced density (1.874g/mm3)
Reduced ash fraction (33.9%)

56
Q

What component of bone is increased in trabecular bone and what effect does this have?

A

Water

Results in lower mineralisation of trabecular and new bone

57
Q

How does the surface area to volume ratio of cortical bone compare to trabecular bone?

A

Lower in cortical bone

58
Q

What are the turnover rates for cortical and trabecular bones?

A 
Cortical = 3%
Trabecular = 26%
59
Q

What are the functional units of cortical and trabecular bones?

A 
Cortical = Osteon (Haversian systems)
Trabecular = Trabeculae
60
Q

Which part of the vertebral cortical bone is thicker? Why is the other part thinner?

A

Ventral shell

Dorsal shell thinner perhaps due to posterior cortex being disrupted by veins and different loading

61
Q

Where is cortical thickness greatest in the vertebral column and why? (Reference?)

A

Greatest in cervical and lumbar regions

Due to Spinal curvatures

62
Q

What is the reference for cortical thickness?

A

Ritzel et al., 1997

Vertebral Column (14 decks)

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