articular cartilage present in joint surface of articulating bone .role of articular cartilage in load bearing is important its damage cause arthritis so should know about its biomechanics

1. BIOMECHANICS OF THE
ARTICULAR CARTILAGE
Dr Susanta kumar khuntiaDr Susanta kumar khuntia
MKCG medical collegeMKCG medical college
Berhampur,OdishaBerhampur,Odisha

3. COMPOSITION AND STRUCTURE OF
ARTICULAR CARTILAGE
2. COLLAGEN (fibrous ultrastructure, procollagen2. COLLAGEN (fibrous ultrastructure, procollagen
polypeptide), 10-30 %polypeptide), 10-30 %
3. PROTEOGLYCAN ( PG ) large protein3. PROTEOGLYCAN ( PG ) large protein
polysaccharide molecules ( in form of monomers andpolysaccharide molecules ( in form of monomers and
aggregates) 3-10 %aggregates) 3-10 %
4. WATER + inorganic salts, glycoprteins, lipids, 60-4. WATER + inorganic salts, glycoprteins, lipids, 60-
87 %87 %
1. CHONDROCYTES, 10 %

5. LOCATION OF THE COLLAGENE FIBERS

7. COMPRESSION

8. CARTILAGE AS VISCOELASTICCARTILAGE AS VISCOELASTIC
MATERIALMATERIAL
If a material is subjected to the action of aIf a material is subjected to the action of a
constant (time independent load or constantconstant (time independent load or constant
deformation and its response varies (timedeformation and its response varies (time
dependent) then the mechanical behavior ofdependent) then the mechanical behavior of
the material is said to be viscoelastic.the material is said to be viscoelastic.

9. PERMIABILITY OF ARTICULAR
CARTILAGE
Porosity ( β ): ratio of the fluid volume (m3
)to
the total amount (m) of the porous material
Permeability ( k ): a measure of the ease with
which fluid can flow through a porous
permeable material and it is inversely
proporsional to the frictional drag ( K )
k = β 2
/ K [(m
4
/Ns

10. Basic responses
1. BIPHASIC CREEP1. BIPHASIC CREEP
2. BIPHASIC STRESS RELAXATION2. BIPHASIC STRESS RELAXATION

11. 1. BIPHASIC CREEP1. BIPHASIC CREEP
The time taken to reach creepThe time taken to reach creep
equilibrium varies inversely with theequilibrium varies inversely with the
square of the thickness of the tissuesquare of the thickness of the tissue

12. CREEP PHENOMENON
CREEP EQUILIBRIUM
• 2-4 mm human and bovin articular
cartilage > 4 - 16 hours
• rabbit cartilage 1 mm > 1 hour
above 1 Mpa > 50 % of total fluid is squeezed
FIG.
2-9

14. The rate of fluid exudation governs the
creep rate, so it can be used to determine
the permeability coefficient
TISSUE PERMEABILITY COEFFICIENT(k)
HUMAN CARTILAGE: 4.7 +/- 0.04 x 10 -15
m4
/ N s
BOVIN CARTILAGE: 4.67 +/- 0.04 x 10 -15
m4
/ N s

15. INTRINSIC COMPRESSIVE MODULUS ( HINTRINSIC COMPRESSIVE MODULUS ( HAA ))
HUMAN CARTILAGE: 0.79 +/- 0.36 MPaHUMAN CARTILAGE: 0.79 +/- 0.36 MPa
BOVIN CARTILAGE: 0.85 +/- 0.21 MPaBOVIN CARTILAGE: 0.85 +/- 0.21 MPa
Equilibrium defomation can be usedEquilibrium defomation can be used
to measure the intrinsic compressiveto measure the intrinsic compressive
modulusmodulus

16. ““k” varies directly with waterk” varies directly with water
contentcontent
““HHAA” varies inversely with water” varies inversely with water
contentcontent

17. STRESS RELAXATION
TISSUE PERMEABILITY (k)
INTRINSIC COMPRESSIVE MODULUS ( HA )
similar to creep

19. UNIAXIAL TENSION

22. Tangent modulus, which denotes the
stiffness of the material
σ / ε
Maximum strain : 3 - 100 MPa,
Physiological strain: 15 % > 5 - 10 MPa
compliancecompliance = ε / σ
szigma, epszilon

23. PURE SHEAR FORCES
No interstitial fluid flow occures
No pressure gradiens or volumetric changes
Thus , a steady dynamic pure shear
experiment can be used to asses the
intrinsic viscoelastic properties of the
collagen - RG solid matrix.

24. PURE SHEAR
storage modulus ( G` ), loss modulus ( G`` )
dynamic shear modulus ( G* )2
= ( G`)2
+ ( G``)2
phase shift angle (phase shift angle ( δ ) =δ ) = tantan −1 (−1 (G``/ G`)G``/ G`)
FIG.
2-15
The magnitude of the dynamic shearThe magnitude of the dynamic shear
modulus is a measure of the total resistancemodulus is a measure of the total resistance
of the viscoelastic materialsof the viscoelastic materials
G* = ( G`)2
+ ( G``)2

25. The magnitude of the dynamic shear
modulus is a measure of the total resistance
of the viscoelastic materials
δ value is a measure of the total frictional
energy dissipation within the material.
In pure elastic material is no internal
frictional dissipation: δ is zero
for pure viscous fluidfor pure viscous fluid δδ is 90 degreeis 90 degree
FIG.
2-15,
16

26. Bovin articalar cartilage
G* = 1 -3 Mpa
δ = 9 - 20 degrees

27. LUBRICATION

28. BOUNDARY
LUBRICATION
FLUID FILM
LUBRICATION
TYPES OF LUBRICATION

29. Absorbed
boundary
lubricant

30. BOUNDARY LUBRICATION
FIG.
2-18
independent of the physical properties
of either lubricant (eg. its viscosity) or
the bearing material (eg. its stiffness),
but instead depends almost entirely on
the chemical properties of the lubricant.
glycoprotein, lubricin
lubricin is adsorbed as a macromolecule monolayerlubricin is adsorbed as a macromolecule monolayer

31. FLUID FILM LUBRICATION
SQUEEZE FILM
LUBRICATION
HYDRODYNAMIC
LUBRICATION

32. FLUID FILM LUBRICATION
Utilizes a thin film of lubricant that causes greater
bearing surface separation
> 20 um

33. HYDRODYNAMIC LUBRICATION
Occurs when nonparallel rigid bearing surfaces
lubricated by a fluid film move tangentially with respect
to each other (i.e. slide on each other), forming a
covering wedge of fluid.
A lifting pressure is generated in this wedge by
the fluid viscosity as the bearing motion drags
the fluid into the gap between the surfaces.

34. SQUEEZE FILM LUBRICATION
Occurs when the rigid bearing surfaces move
perpendicularly towards each other. In the gap between
the two surfaces, the fluid viscosity generates pressure,
which is required to force the fluid lubricant out.
The squeeze film mechanizm is sufficient to carry high
loads for short duration

36. In the hydrodynamic and squeeze film
lubrication, the thickness and extent of fluid
film, as well as its load-bearing capacity, are
characteristics independent of rigid bearing
material properties.
Determined by
• reologic properties (viscosity)
• the film geometry ( the shape of the gap)
• speed of the relative surface motion

37. Elastodynamic lubrication

38. (surface of the bearing material is not smooth)

39. Self-lubrication

40. The effective mode of lubrication depends on the
applied loads and on the velocity (speed and
direction) of the bearing surfaces.
Boundary lubrication: high loads, low speed, long periods
Fluid film lubrication: low loads, high speed
combinations
Elastohydrodynamic lubrication: the pressure
generated in the fluid film substantially deforms
the surface

41. Summary
1. Elastohydrodynamic fluid film of both sliding
(hydrodynamic)and the squeeze type probably play an
important role in lubricating the joints
2. With high load and low speed of relative motion,
such as during standing, the fluid film will decrease in
thickness as the fluid is squeezed out from between the
surface.
3. Under extreme loading conditions, such as during
extended period of standing following impact, the fluid
film may be eliminated, allowing surface-to- surfabe
contact.

42. WEAR OF ARTICULAR CARTILAGE
1. INTERFACIAL (ABRESIVE) WEAR
interaction of bearing surfaces
2. FATIGUE WEAR
accumulation of microscopic damage
(disruption of the collagen-PG matrix)
within the bearing materials under
repetitive stressing
erosion

43. BIOMECHANICS OF CARTILAGE
DEGENERATION
Failure progression relates
• magnitude of the imposed stresses
• total number of sustained stress peaks
• changes in the intrinsic molecular and
microscopic structure of the collagen-PG
matrix
• changes in the intrinsic mechanical property
of the tissue