Week 2

Question 1

What type of nodes are there in imaging methods for bone?

Answer 1

2D projection: x-ray, DEXA.

2D cross-sectional: invasive (microtome) & non-invasive ( CT, MRI)

3D: invasive (microtome) & non-invasive ((whole body) CT, MRI) –> combination of multiple cross-sections.

Question 2

Characterisations of

1. X-ray/ CT
2. DEXA
3. MRI
4. Sectioning (histology)

Answer 2

Characterisations of
1. X-ray/ CT: differences in X-ray attenuate of tissues. Surrounding tissues also absorb radiation (not quantitative for bone).

2. DEXA: differences in absorptiometry of bone only.
3. MRI: differences in water concentration.
4. Sectioning (histology): differences in color after staining.

Question 3

How can you quantify cancellous bone microstructure?

Answer 3

1. Amount of bone tissue
2. Directionality trabeculae
3. Geometry & connectivity trabeculae

Question 4

What are the parameters & equations to determine the amount of bone?
Amount of bone: 
Volume fraction:
Porosity:
Volumetric bone density:

Answer 4

Amount of bone:
areal bone mineral density (aBMD) [g/cm2] / bone mineral content (BMC) [g]

Volume fraction: bone volume (BV) / total volume (TV)

Porosity: 1- BV/TV

Volumetric bone density (BMD)= total mass [kg/m3] / total volume [g/cm3].

Question 5

What are the parameters & equations to determine the directionality of bone?

Answer 5

Directionality:

Mean intercept length (MIL) = total length (L) / #transitions to bone (I(w)).

Question 6

What are the parameters & equations to determine the geometry & connectivity trabeculae bone:

Tb.N, Tb.Th, Tb. Sp, Conn.D =

Structure Model Index (SMI)=

Answer 6

Geometry constrituive elements: 
Trabecular number: Tb.N
Trabecular thickness: Tb.Th
Trabecular separation: Tb. Sp
Connectivity density: Conn.D

Other 3D parameters:
Structure Model Index (SMI)= equation with tissue volume and tissue surface. The number/gain (-3 till 3) determines the shape.

Question 7

Mechanobiology=

Mechanotransduction=

Answer 7

Mechanobiology= focuses on the way that physical forces and changes in cell or tissue mechanics contribute to development, physiology or disease.

Mechanotransduction= any of various mechanisms by which cells convert mechanical stimuli into electrochemical activity.

Question 8

Bone modeling=

Remodeling=

Answer 8

Bone modeling= bone resorption and formation occur independently at different sites to sculpt one (i.e. during growth and/or response to mechanical loading).

Remodeling= process of bone renewal throughout life during which small packets of bone are removed and subsequently replaced within the basic multi-cellular unit (BMU).

Question 9

How does bone responds to mechanical load?

Answer 9

Steps: mechanical load > fluid flow in canaliculi > mechanosensing by osteocytes > bone remodeling by osteoclasts & osteoblasts.

Force transmission on tissue level: Physical forces acts on bone on the tissue level.
Force transmission on cell level: (static) mechanical properties of the matrix surrounding the cells & mechanical forces acting on the cell.

Reaction on tissue level: bone mass + alignment –> structural change.
Reaction on cell level: electrochemical and biological responses –> change in cellular acitivity.

Question 10

What is the difference between bone remodeling on trabecular bone and cortical bone?

Answer 10

Trabecular bone remodeling: osteoclasts create Howship’s lacunae that are refilled by osteoblasts.

Corticol bone remodelling: the osteoclasts erode bone tissue and are followed by osteoclasts that repopulate/refill the gap with new bone. So a tunnel in the bone is made for a bloodvessel and cells/ nutrients work from within.

Question 11

Low/high strain results in formation/ resorption of bone.

Answer 11

Low strain: resorption.

High strain: formation.

Question 12

Why is it necessary to have osteocyte viability & osteocyte apoptosis?

Answer 12

Osteocyte viability: maintenance of bone homeostasis/ integrity.

Osteocyte apoptosis: essential for damage repair and normal skeletal replacement. Apoptotic osteocytes are often in contact with osteoclasts. These osteoclasts resorb apoptotic osteocytes. Osteoblasts misses a signal from osteocytes and start making bone.

Question 13

How does wall shear stress influence osteogenesis?

Answer 13

<0.11 mPa: too low stimuli
0.11-0.55 mPa: osteogenesis (no mineralization)
0.55-10 mPa: osteogenesis (mineralization)
>10 mPa: too high stimuli