Joints, articular cartilage and synovial fluid L1: Biomechanics of cartilage and synovial fluid Flashcards
What is kinematics?
Describes the motion of objects
- No reference to mass of object or force which causes motion
In most synovial joints, there is a comination of ____ and ____. Example: abduction of GHJ and tibiofemoral joint
Rotation and translation
- Eg. Abduction of GHJ
- Superior translation
- Rotation
- Eg. tibiofemoral joint
- Rot and trans. Discrepancy in articular surfaces
Whaat is the instaneous centre of rotation (ICR)?
- “the theoretical axis (centre) of rotation at a specific joint position”
- At a specific moment in time
- Rotation &; translation occur stimultaneously –> Axis (CoR) is moving
What are 2 examples of external force?
- Gravity
- ground reaction force
What are 2 examples of internal force?
- Active contractions from muscles
- passive resistance
Is force linear or angular?
Linear
Is moment linear or angular? What is the moment?
Angular
Force x distance (moment arm- perpendicular distance from CoR to line of action)
What is friction?
Frictional forces resist the movement of an object
What are the 4 features of synovial joints?
- Graduated flexibility
- Variable bearing area
- Articular cartilage
- Synovial fluid
How is graduated flexibility related to synovial joints?
- Articular cartilage –> spongy bone –> compact bone (stiffness)
- Diaphysis = compact bone
- Epiphysis = spongy bone
How is variable bearing area related to synovial joints?
- When jts move, muscles apply compression
- Contact area, where force is going across, affects stress
- Stress = force/area o EG. habitual postures
How is articular cartilage related to synovial joints?
- Hyaline cartilage (most jts)
- Fibrocartilage (ACJ and pubic symphysis)
How is synovial fluid related to synovial joints?
Nutrition
(Increased/decreased) co-efficient due to jt surface (smooth, quality of surface shape, amount of co-contraction) = (Increased/decreased) frictional force
Increased
Increased
Hyaline cartilage cells (chondrocytes) are in ______. (Sparse/dense)
Lacune sparse
Hyaline cartilage has _______ (highest/lowest) cell density.
Lowest
Poor ability to repair
Hyaline cartilage is ______ (vascular/avascular)
Avascular
Poor ability to repair
Dense regular connective tissue proper (DRCTP) is ______ (dense/sparse).
Dense
Dense regular connective tissue proper (DRCTP) is ________ aligned.
Regularly
Dense regular connective tissue proper (DRCTP) are made up of ___blasts and ____cytes.
fibroblasts
fibrocytes
Fibrocartilage is a combination of _________ and _________.
Connective tissue proper
Hyaline
What is an example of fibrocartilage
- Meniscus
- Pubic symphysis
Comparison between hyaline cartilage and fibrocartilage: Type of cell
H: Chondrocytes
F: Chondrocytes and fibrocytes
Comparison between hyaline cartilage and fibrocartilage H20
H>F
70-85% : 60-70%
Comparison between hyaline cartilage and fibrocartilage: Collagen
H: Type II
F: Type I
Both 15-20% by mass
75% dry weight
Comparison between hyaline cartilage and fibrocartilage: Fibre orientation
H
Superficial: parallel
Middle: random
Deep: perpendicular
F
AF: circumferential
Meniscus: circumferential and radial
Comparison between hyaline cartilage and fibrocartilage: Proteogylcan
H> F
<10% : 1-2%
Collagen structure resists ____ forces.
Tensile
The collagen structure depends on ____ they are made of and ________.
Substance
cross-sectional area
The shape of cross-section of collagen is ____ and _____.
Immaterial
Simple
Collagen structure is 4-10 times stronger than it needs to be. This is called ______.
Safety factor
- What it needs to withstand vs what it can withstand
- Subdivision- failure in one area doesn’t mean failure in all
Collagen structure is hellical. True or false?
True
Bundle together fibrils
Collagen structure has a staggered offset. True or false?
True
What is a proeogylcan?
A protein core wth side chains of chondroitin sulfate ad keratin sulfate
What is a proteoglycan aggregate?
- Proteoglycans (green) bound to a hyaluronic acid backbone
- Increased compression = increased resistance (-ve) = bottle brush shape (puff)
How is the cartilage ECM created?
- Repulsion of proteoglycan contained by collagen mesh-net
- Pre-stressed
- -ve charged ions attach ions (from synovial fluid) –> move into cartilage –> water flows in as well
What is the tide mark?
Between calcified & non-calcified cartilage
What is the fibre orientation of cartilage ECM?
- Superficial = parallel (more collagen than proteoglycan)
- Middle = random (more proteoglycan)
- Deep = vertical (collagen)- anchor into calcified cartilage
What are the 2 phases of the biphasic model of cartilage?
- Fluid phase
- Solid phase
What is the fluid phase of the biphasic model of cartilage?
- Fluid depends on rate of application of force
- Eg. smack water vs slowly dip water
What is the solid phase of the biphasic model of cartilage?
- Cells
- Collagen types I & II
- Proteoglycans
Solids that have ______ mechanical behaviour, because of a fluid-like component are ______.
time-dependent viscoelastic
- Creep (constant load)
- Stress relaxation (constant strain = stress)
What are the 3 components that compression of the solid phase is resisted by?
- Viscous drag
- Electrostatic repulsion
- Osmotic swelling
What is viscous drag and how does it resist compression of solid phase?
- Resistance to flow
- Water, synovial fluid = visocity
What is electrostatic repulsion and how does it resist compression of solid phase?
- Resist compression of cartilage
- Maintain area = resolve deformation
What is osmotic swelling and how does it resist compression of solid phase?
- –ve proteoglycans –> attack +ve –> Water flows in
What fibre type is best at withstanding force?
Type I
Cartilage is _____ compliant than bone.
More
What is permeability?
how easily fluid can move out
Both hyaline and fibrocartilage have _____ permeability.
Low
Hyaline cartilage can withstand _____ compressive forces than fibrocartilage.
More
Twice as much
What is bearing?
A part of a machine that allows one part to rotate or move in contact with another part with as little friction as possible
What is binding?
The action of fastening or holding together
What are the 2 types of mixed lubrication?
- Fluid-film lubrication
- Boundary layer lubrication
What is fluid-film lubrication?
- Thin film of lubricant btn articular surfaces in contact
- Load is supported by pressure developed in fluid
- Fluid film needs to be >3x surface roughness
- Viscosity is important (hyalonurate)
- Pressurised fluid o Separates articular surfaces
- Decreased co-effiecient of friction
What is boundary layer lubrication?
• Surfaces are protected by a boundary lubricant (lubricin) • Prevent contact of articular surfaces
