Basic Science Flashcards
Strain and stress definitions and units
Strain = percentage change in length (given as %)
Stress = force per unit area (N/mm2 or Pa)
Hooke’s Law
Stress = Young’s modulus (E / Elastic modulus) x strain
i.e. E is slope of the line
Poisson’s ratio
Range
- cork
- rubber
Ratio of transverse strain an object undergoes to the axial strain that is applied
Higher ratio = more “squash able”
Must be -1 to 0.5 Most between 0 - 0.5. Cork 0 (compressible), rubber 0.5 (incompressible)
Isotropic
Anisotropic
Orthotropic
How many constants to define their elastic modulus
How many constants to define deformation
Isotropic - same properties each direction - 2 constants
Anisotropic - different properties in each direction - 5 constants
Orthotropic - three perpendicular planes of symmetry - 9 constants
6
Draw stress strain curve
Definition and example:
- Creep + e.g.
- Stress relation + e.g.
- Endurance limit
- Stress shielding
Stress remains constant and strain increases - ACL graft
Constant strain and a reduction in stress - Ponsetti casting
Highest stress to withstand >10 million cycles
Bone protected from stress so less load so loss of bone mass
3x types of wear and definition
Abrasive - friction between hard and soft material
Adhesive - molecular affinity between two surfaces
Fatigue - delamination / microscopic wears
Mechanism of osteolysis around biomaterials
Macrophages ingest particles, release TNF-alpha and IL-1 - osteoclastic resorption
Definition
- casting
- machining
- forging
- cold working
- annealing
- sintering
casting - melted, moulded and cooled
machining - removing small imperfections
forging - compressed between moulds into final shape
cold working - shaped below its recrystallisation temperature
annealing - heated to just above recrystallisation temperature
sintering - compressing by heat and/or pressure without melting it
Effects of cold working and of annealing
Cold working - harder, stiffer, stronger, but less plastic so cracks easier. Decreases grain size
Annealing - more ductile, less hard
Cold working effect on
- toughness
- hardness
- tensile strength
- yield stress
- ultimate stress
- brittleness
- ductility
- toughness - ↑
- hardness - ↑
- tensile strength - ↑
- yield stress - ↑
- ultimate stress - ↑
- brittleness - ↑
- ductility - ↓
Stainless steel
- composition
- carbon content and why
- corrosion
- one good specific property
Iron > chromium > nickel > carbon
Carbon <0.03% - reduces corrosion
Resists corrosion well, but susceptible to crevice corrosion and to galvanic corrosion at boundaries (e.g. with CoCr head)
Ductile (ultimate stress»_space;> yield stress)
Cobalt chrome
- composition
- what type of alloy
- ductility and wear
60% cobalt / 28 % chromium
Biphasic alloy
very low ductility, very good wear properties
Titanium
- grade 5 alloy
- good and bad property for arthroplasty
- compared with pure titanium, the alloy is__
- resistance to corrosion
- Ti6Al4V
- rough finish allows for interlocking
poor wear properties - stronger
- better than steel and cobalt alloys
Standard THR composition
Titanium cup
Titanium uncemented stem
Stainless steel cemented stem
Co-Cr or ceramic head
Young’s modulus of:
stainless steel
Co-Cr
titanium
cortical bone
190 GPa
230 GPa
110 GPa
17 GPa
Polyethylene
- type of bonds
- strength depends on
- stability depends on
covalent and van der Waals
strength - molecular weight
stability - temperature
Bone cement
- name
- powder consists of:
- liquid consists of:
- viscosity is:
- Young’s modulus is
polymethylmethacrylate
powder - PMMA beads, radio pacifier (barium), initiator (dibenzyl peroxide), dye
liquid - activator (methacrylate monomer), accelerator (toluidine), hydroquinone (stabiliser)
viscosity is low
between cortical and cancellous bone
Density of UHMWPE is close to:
Method of irradiation
How does irradiation change UHMWPE
Closer to low than high density PE
Gamma irradiation with Co60 source
improves wear characteristics but decreases fatigue and fracture resistance
Ceramics
- Friction coefficienty
- Hardness
- Brittleness
- Biocompatibility
- Strength is inversely proportional to:
Aluminia -
Zirconia -
very low
high
high
high
grain size and porosity
very low coefficient of friction, high wettability, fractures
stronger and denser but rougher
Metallic bonds
- structure
- charge
crystalline array - positive nuclei with loose valence electrons
Neutral
Synovial fluid
- Components missing from plasma
- viscosity
- Newtonian? and why
- effect on coefficient of friction of the joint
- change in septic arthritis
- change in rheumatoid arthritis
- hyaluronate is a ___ and not a ___
no clotting factors / erythrocytes
high viscocitiy
NOT newtonian because of hyaluronate
lowers coefficient of friction, at low loads
higher glucose, but not as high as plasma
less viscous due to degraded hyaluronate
GAG, not a PG
Newtonian fluid definition
Viscosity remains at a constant no matter the shear forces applied. And energy is not stored
Draw the growth plates
Growth plates:
Reserve zone
- oxygen tension
- collagen
- chondrocytes
- calcium
Proliferative zone
- cell shape
- oxygen tension
- specific disease affects here
- calcium
- fails here in ___
Hypertrophic zone
- responsible for ___
- vascularity
- strength
- low oxygen, disorderly collagen, single layer chondrocytes, high calcium
- flattened cells, highest oxygen, achondroplasia, high calcium but more ionised, tension
- mineralisation, avascular, weakest point
Draw the growth plates
Where is fibrocartilage and elastic cartilage
- transitionally in fractures. Menisci, TMJ and IV discs
- Eustachian tube, epiglottis
Cartilage ECM
- what are the regions
- what is it made up of
pericellular - thinnest, no collagen, high PG
territorial - protects chondrocytes
interterritorial - largest, packed collagen
- water, aggrecan, type II collagen, lubricant
What is the tidemark and where is it
junction between calcified and uncalcified cartilage - lacerations that don’t cross it don’t heal - it is beneath the deep zone
Zones of cartilage cartilage
- thickness, collagen, chondrocytes, aggrecan, water
Collagen
- isotropic / orthotropic / anisotrophic
- tensile strength compared with meniscus
- type in cartilage
orthotropic
less
type II (except type 5 around chondrocytes)
Collagen
Type 1 found in
Type 2 found in
Type 2 cross linked by
Type 3 found in
Type 5 found in
1- bone, outer meniscus, ligaments, tendons, scar in articular cartilage
2 - articular cartilage, inner meniscus, woven bone
cross linked by type IX
3 - sites of healing and repair
5 - peri-cellular matrix of cartilage
What are the proteoglycans in articular cartilage
What is their function
What properties do they provide
What increases proteoglycan release/breakdown from cartilage
aggrecan
dermatan
chondroitin
keratan
- to attract water
- compressive stiffness and durability
- IL-1 and immobilisation
Percentage dry weight that is collagen in
- fibrocartilage
- hyaline cartilage
- tendons
- ligaments
70
50-80
86
70
Menisci
- composition
- types of collagen
- percentage load of knee taken
- when does collagen decrease
- ligaments from lateral meniscus
- structure of layers (which one responsible for load transmission)
- cells in layers
70% water, most of rest collagen
outer type 1, inner 60/40 2/1
50% ext, 85% flex
collagen decreases after 80
to MFC with Wisberg and Humphrey
random superficially, middle parallel (load transmission), deep circumferential
fusiform in superficial, ovoid in deep
Composition of bone
60% inorganic
- hydroxyapatite - calcium and phosphate
30% organic
- type 1 collagen 90%
- proteoglycans
10% water
Haversian systems and Volkmann’s canals
Haversian systems - tubes that run within axis of bone
Volkmann’s canals - perforating channels that run transversely
Bone
- tropic?
- compression modulus ___x higher than tension
- tension modulus ___x higher than shear
transversely isotropic
1.5x higher
5x higher
Osteoblasts
- function
- at end of life span the:
- surface receptors for:
Osteoclasts
- surface receptors for:
- how to distinguish from macrophages
- how are they made
- lie within:
Osteocytes
- connected by:
OB
- synthesise the extra-cellular matrix
- 10-20% become osteocytes, 10-20% bone lining cells, 60-80%apoptose
- PTH and 1.25 vit D
OCL
- calcitonin only
- secrete enzymes including TRAP
- fusion of monocytes
- Howships lacunae
OCY
- canaliculi
Difference in bone loss in osteoporosis between males and females
Males lose more cortical
Females lose more cancellous
Woven bone
- collagen is:
- cells are:
- where is it seen
randomly aligned type II
ovoid cells
neonates, metaphysis of growing bones, callus, tumours, Paget’s, OI
Primary bone healing:
- how much strain is acceptable
- what initiates remodelling
- gap must be:
2%
cutting cones
<500 microns