Week 2 - Bone Biomechanics

Question 1

Inorganic component of bone and purpose

Answer 1

Provides brittleness and compressive strength

Question 2

Organic component of bone and purpose

Answer 2

Provides flexibility, ductility, tensile strength

Question 3

Purpose of secondary osteons

Answer 3

Create layered structurees within bone for calcium to be stored (Haversian systems)

Question 4

Cortical vs Trabecular bone on stress/strain graph

Answer 4

Cortical bone is much stiffer > therefore less susceptible to deformation

Trabecular bone is much tougher but elastic > deforms more easily

Question 5

Purpose of cortical and trabecular bone structure

Answer 5

Cortical - provides lever
Trabecular - weight bearing

Question 6

How is bone susceptible to fatigue

Answer 6

As you increase the loading cycle, permanent micro-strain and increased deformation occurs

Question 7

Bones are able to resist different amts of force in different directions - what is the order

Answer 7

• most resistance in compression
• slightly less tension
• a lot less in transverse tension

Question 8

Bone adjusts depending on the load - what is the relationship

Answer 8

As rate of loading increases
- bone becomes more brittle & strong
- has a higher ultimate stress BUT
- a lower maxmium strain

Question 9

What does bone failure depend on

Answer 9

Direction and rate of loading

Question 10

What are the 3 types of bone cells, their purpose & location

Answer 10

Osteoblasts - create - surface
Ostecytes - maintain - lacunae
Osteoclasts - break down - howships lacunae

Question 11

How is bone maintained

Answer 11

Maintained through constant state of apposition and resorption
via hormones and external stimuli (mechanotransduction)

Question 12

Type of ossification

Answer 12

Endochondral - long bones
Intramembranous - flat/irregular

Question 13

Purpose of mesenchymal stem cells

Answer 13

Differentiate into periosteal and endosteal surfaces to help thicken cortical bone

Question 14

Osteoprogenitor cell purpose

Answer 14

help form osteoblasts

Question 15

Bone lining cell purpose

Answer 15

Regulate mvt of calcium in and out of matrix and helps osteocytes maintain health

Question 16

Two types of osteocytes and purpose

Answer 16

Quiet/inactive
Formative - making some matrix or resorptive

Question 17

Osteoclast purpose

Answer 17

Eating cells of bone, resorb bone matrix

Question 18

Aging process of bone: newborn-adult

Answer 18

• bone number increases
• mineralisation increases
• bone size increases
• bone proportions change

Question 19

How does bone modelling happen in length growth vs bent growth

Answer 19

Length
- diameter increases in response to length increase
- cross-section increases
- reabsorption occurs to increase medullary cavity

Bent
- One side of periosteal layer has osteoblasts to deposit bone
- other side has osteclasts resorbing
- results in original bone gone and new bone forming new shape

Question 20

Process of Haversian system formation

Answer 20

• osteoclasts form ditch
• osteoblasts fill in perimeter of ditch
• lamellae bone forms ring structure
• blasts become cytes and complete a new osteon

Question 21

Trabecular bone remodelling

Answer 21

• surface is dug up
• filled again with new layer

Question 22

Conditions that are result of imbalance of resorption and formation

Answer 22

• osteoporosis
• osteopenia

Question 23

Why does remodelling of bone occur

Answer 23

Calcium - body pulls calcium from bone, needs to replace it
Microdamage - happens daily, needs to be replaced to stop further damage

Question 24

What is osteopetrosis

Answer 24

• remodels too much, with resorption not occuring, but NOT strong

Question 25

What is Wolffs Law

Answer 25

bone will change in mass and geometry to meet physical demands placed upon it

Question 26

What is the mechanostat theory

Answer 26

bone adapts to function mechanically as required by detecting and responding to loads

Question 27

Mechanostat concept graph sections

Answer 27

Trivial - not much force, would rather absorb Physiological - amt of load is adequate to current bone structure Overload - current structure can't cater to strain and prompted to remodel Pathological - bone cannot keep up and will be damaged

Question 28

Mechanotransduction phases

Answer 28

1. mechanocoupling 2. biochemical coupling 3. transmission 4. effector cell response

Question 29

Mechanocoupling

Answer 29

force applied to bone generates strain > affects cells within > couples mechanical force

Question 30

Biochemical coupling

Answer 30

induce biochemical response in cells

Question 31

Transmission (mechanotransduction)

Answer 31

signal of sensor cell to effector cell cells that experience strain > cells that can do something about it

Question 32

Direction and adaptation of mechanotransduction

Answer 32

- starts within centre and works out towards surface - osteocytes help deposit bone matrix to surface (stiffens)

Question 33

What is microgravity

Answer 33

- decrease in stress on bones e.g. bedrest or astronauts - 4-6 month exposure - decrease in cortical thickness - increase in porosity

Question 34

How do we get bone back after bedrest

Answer 34

increased frequency of loading with spaced breaks

Question 35

Bone failure in acute loading

Answer 35

- fractures - safety factor - how much bone is available and needed to prevent fracture

Question 36

When is safety factor reached

Answer 36

force greater than bone can withstand - can be due to acute MOI - or fatigue loading (progressive degradation in stiffness under repetitive load)

Question 37

How does our body protect us from fatigue fracture

Answer 37

intracortical remodelling - secondary osteon of new bone to replace damaged resists propagation of damage - structures within bone

Question 38

Difference between trabecular and cortical bone in deformation

Answer 38

trabecular - 15% strain not even reaching plastic region cortical - 2% strain it does

Question 39

How does a collapsed vertebrae occur

Answer 39

loss or weakness of horizontal trabeculae with allows vertical struts to buckle

Question 40

Transverse fracture

Answer 40

- force from side - requires less force - breaks at 90 angle to long axis of bone

Question 41

Comminuted fracture

Answer 41

- more than two bone components created - high rate of loading

Question 42

Stress fractures

Answer 42

- occurs over time - mismatch of bone strength and stress it gets - repetitive forces

Question 43

greenstick fracture

Answer 43

- partial - only cortex and periosteum interrupted - common in children (have more collagen)

Question 44

Osteopenia v osteoporosis

Answer 44

Penia - low bone mass Porosis - low bone mineral density

Question 45

How does trabecular remodelling change with age

Answer 45

1. Adaptive - preferential remodelling of unloaded bone and maintenance of loaded 2. metabolic - uniform thinning 3. microdamage - preferential remodelling of damaged struts