Cartilage has three main types - hyaline, elastic, and fibrocartilage. Hyaline cartilage lines joints and provides a smooth gliding surface. Fibrocartilage is strong and resilient, found in intervertebral discs and menisci. Elastic cartilage is flexible, in the larynx and ear. Cartilage is composed of water, collagen fibers, and proteoglycans that give it strength and resilience. With aging, cartilage calcifies and stiffens. Immobilization and excessive/repetitive loads can damage cartilage over time by altering biomechanics and reducing nutrient flow. Regular exercise preserves cartilage by stimulating metabolism and matrix synthesis through mechanical loading.

1. Biomechanics of Cartilage
Sunil
MPT – 1 SEM

3. Fibrocartilage
White Fibrocartilage contains bundles of white fibrous tissue
which give it great tensile strength with some elasticity, so
that it is able to resist considerable pressure.
• Intervertebral discs
• Menisci of knee joint
• Labrum surrounding and deepening the glenoid fossa of
shoulder joint
• Articular discs of radiocarpal, strenoclavicular, AC and
temporomandibular joint.
• White fibrocartilage may calcify and ossify

4. • All three structures are composed of water, collagen,
and proteoglycans (PGs)
• Nucleus Pulposus: 70% to 90% water, depending on
age and time of day. Collagen fibers contribute 15%
to 20% of the dry weight and 65% is of PGs.
• Anulus Fibrosus: Collagen fibers make up 50% to 60%
of the dry weight. And 10% elastin.
• Vertebral End Plates: 0.6 to 1mm thick, both hyaline
cartilage and fibrocartilage present. But with
increasing age, no hyaline cartilage remaining

5. ELASTIC CARTILAGE
• Yellow Fibrocartilage contains bundles of elastic fibres with
little or no white fibrous tissue.
• It does calcify or ossify and is not found in musculoskeletal
system.
• Elastic cartilage is found in the epiglottis, larynx and the
pinnae.

6. HYALINE CARTILAGE
• Hyaline cartilage forms the temporary skeleton of the fetus
from which bones develop. Its remnants can be seen as the
articular cartilages of synovial joint, the epiphyseal growth
plates between parts of an ossifying bone during growth, and
the costal cartilages of the ribs.
• It has a white, lustrous and smooth appearance.
• It provide a smooth surface permitting free movement to
occur and resist the compressive forces encountered across
the joint under loading.
• With increasing age, hyaline cartilage tends to become
calcified and sometimes ossified.

7. Biomechanics of Articular Cartilage

8. Microstructure of cartilage
• The cells of cartilage are chondroblasts and chondrocytes.
• Chondrocytcs manufacture, secrete, organize and maintain
the organic component of the extracellular matrix.
• The organic matrix, is composed of dense network of fine
collagen fibrils.

9. WATER
• The fluid component of articular cartilage is also essential
to the health of this avascular tissue because it permits gas,
nutrient, and waste product movement back and forth
between chondrocytes and the surrounding nutrient-rich
synovial fluid
• Most of the water thus occupies the inter space of the ECM
and is free to move when a load or pressure gradient or
other electrochemical motive forces are applied to the
tissue.
60 to 85% is water

10. COLLAGEN
• Collagens consist of 3 polypeptide chains
that form a triple helix
• They can be divided into fibrillar
collagens(types I, II, III, V and XI), which
form the framework of the tissue
60 to 70% of the dry weight

11. • More than 20 different types collagen identified so far, the
functions of all of these types have not been determined.
• The fibril-forming collagens (types I, II, III, V, and XI) are the
most common.
• Type I collagen, comprising 90% of the total collagen in the
body, is found in almost all connective tissue, including
tendons, ligaments, menisci, fibrocartilage, joint capsules,
bones, labra, and skin.
• Type II collagen is found mainly in hyaline articular cartilage
and in the nucleus pulposus in the center of the intervertebral
disks.
• Type III collagen is found in the skin.

12. • Collagens—
structure,
function, and
biosynthesis
• K. Gelsea, E.
Po¨schlb, T.
Aignera,*

13. PROTEOGLYCAN
.
A large protein-polysaccharide molecule composed of a protein core
to which one or more glycosaminoglycans (GAGs) are attached.
30% of the dry weight

14. STRUCTURAL AND PHYSICAL INTERACTION
AMONG CARTILAGE COMPONENTS
• The closely spaced sulfate and carboxyl
charge dissociate in solution at
physiological pH leaving a high
concentration of fixed negative charges
that create strong intramolecular and
intermolecular repulsive forces.
When cartilage is compressed, the negatively charged sites on
aggrecan are pushed closer together, which increases their mutual
repulsive force and adds to the compressive stiffness of the
cartilage.

15. • Collagen fibrils and PGs, each being capable of
forming structural networks of significant
strength.
• These structural components support the
internal mechanical stresses that result from
loads being applied to the articular cartilage.

17. MATERIAL PROPERTIES
• A confined compression test commonly used methods for
determining material properties of cartilage.
• A “creep” mode : a constant load is applied to the cartilage
through a porous plate, and the displacement of the tissue is
measured as a function of time

18. • In relaxation mode : a constant displacement
is applied to the tissue, and the force needed
to maintain the displacement is measured.

19. Aggregate modulus and permeability
• The aggregate modulus is a measure of the stiffness of the
tissue at equilibrium when all fluid flow has ceased.
• The higher the aggregate modulus, the less the tissue deforms
under a given load.
• The average fluid velocity is proportional to the pressure
gradient
• The constant of proportionality is called the permeability.
• The aggregate modulus of cartilage is typically in the range of
0.5 to 0.9 Mpa.
• The Young’s modulus of cartilage is in the range of 0.45 to
0.80 MPa.

20. Stress and strain

21. Young’s modulus

22. • If the fluid flowed easily out of the tissue, then the solid
matrix would bear the full contact stress, and under this
increased stress, it might be more prone to failure.
• The lower modulus and increased permeability of
osteoarthrotic cartilage result in greater and more-rapid
deformation of the tissue than normal.

23. • Compression is minimized because of the high proteoglycan
concentration, and this serves to protect the chondrocytes from
adverse forces.
• This protection breaks down when the joint is subjected to
excessive loads or overuse, as the chondrocytes release
proteolytic enzymes which damage the proteoglycan and
collagen so causing tissue degeneration
In general, dynamic (cyclic) loading is beneficial to matrix
synthesis, whereas static loading is detrimental
• Abnormally high compression loads may lead to articular
cartilage changes and deterioration

24. MECHANICAL FAILURE OF CARTILAGE
• A characteristic feature of osteoarthrosis is cracking,
fibrillation, and wear of cartilage.
Studies of the tensile failure of cartilage are primarily
concerned with variations in properties among joints, the
effects of repeated load, and age.

25. • Repeated compressive loads applied to the
cartilage surface in situ also cause a decrease
in tensile strength, if a sufficient number of
load cycles are applied.
• Repeated tensile loading (fatigue) lowers the
tensile strength of cartilage as it does in many
other materials. As the peak tensile stress
increases, the number of cycles to failure
decreases

26. The effects of repeated tensile loading on the tensile strength of cartilage.
As the tensile loading stress increases, fewer cycles of loading are needed to
cause failure.
Age is also an important factor.Cartilage from older individuals fails at a lower
stress than that from younger people.

27. JOINT LUBRICATION
Lubrication of articulating cartilage surfaces by SF is mediated by
several lubricant macromolecules synthesized and secreted by
synovial cell populations and found in SF.
• Normal synovial joints operate with a relatively low coefficient
of friction, about 0.001
• Identifying the mechanisms responsible for the low friction in
synovial joints has been an area of ongoing research for
decades

28. • From an engineering perspective, there are two fundamental
types of lubrication.
• One is boundary lubrication, which involve as a single
monolayer of lubricant molecules adsorbed on each bearing
surface.
• The other is fluid-film lubrication, in which a thin fluid-film
provides greater surface-to-surface separation
• Combination of boundary lubrication (at low loads) and fluid
film lubrication (at high loads) is responsible for the low
friction in synovial joint

29. Hypotheses on the Biomechanics
of Cartilage Degeneration
ROLE OF BIOMECHANICAL FACTORS
• Magnitude of the imposed stresses.
• The total number of sustained stress peaks.
• The changes in the intrinsic molecular and microscopic
structure of the collagen-PG matrix.
• The changes in the intrinsic mechanical property of the
tissue.
• Loosening of the collagen network, that allow abnormal PG
expansion and thus tissue swelling.

31. IMPLICATIONS ON CHONDROCYTE
FUNCTION
• In healthy articular cartilage, loads from
normal joint function motion result in the
generation of mechano-ectrochemical stimuli
that promote normal cartilage maintenance.
• trauma or disease leads to abnormal
mechano-ectrochemical stimuli,

32. MODELS OF OSTEOARTHROSIS
• Animal models are used to provide a controlled environment
for studying the progression of osteoarthrosis.
• various mechanical alterations of a joint lead to the
development of osteoarthrosis.
• Surgical alterations may be small, suggesting that altered
forces are primarily responsible for the developing
osteoarthrosis.
• Impulsively applied loads were found to produce
osteoarthrosis, while higher loads applied at a lower rate do
not

33. Effects of aging on articular cartilage
Changes in cells
• Reduced cell density,
• Reduced responsiveness to growth factors.
Changes in extracellular matrix
• Increase Advanced glycation end-product (AGEs)
• The cumulative effect of mechanical load over the
years may cause “wear and tear”
Effects of aging on articular cartilage homeostasis by Martin Lotz a,, Richard F. Loeser b

34. • There is evidence showing that HMGB2, a high-mobility group
box (HMGB) protein that may be important for chondrocyte
survival, Decline in HMGB2 levels was associated with
increased chondrocyte death.
• Levels of Reactive oxygen species (ROS) are increased in
cartilage during aging, and chondrocytes from older adults are
more susceptible to ROS mediated cell death.
• Mechanical injury to cartilage, such as articular cartilage
crushing, shearing force injury, would result in elevated ROS
generation in mitochondria and promotes chondrocyte death.
• Evidence has been shown that mitochondrial DNA damage in
OA is promoted by inflammatory cytokines such as IL-1𝛽 and
tumor necrosis factor- 𝛼 (TNF-𝛼 ) and contributes to
chondrocyte death
The Age-Related Changes in Cartilage and Osteoarthritis
YongPing Li,1 XiaoChun Wei,1 JingMing Zhou,2 and Lei Wei1,2

35. • During aging, chondrocytes exhibit reduced responsiveness to
growth factors, such as insulin-like growth factor-1 (IGF-1) ,
osteogenic protein-1 (OP-1) or bone morphogenic protein-7, and
transforming growth factor-𝛽 (TGF-𝛽)
• For example, TGF-𝛽 stimulates proteoglycan synthesis in young
animals, but this ability is impaired in old mice
• In chondrocytes, AGEs can increase the production of
inflammatory cytokine (TNF-𝛼), inflammatory mediators
prostaglandin E2, and nitric oxide. It can also suppress the
production of type II collagen.

36. ECM
• Advanced glycation end-product (AGEs) increase collagen
cross-linking, which enhances tissue stiffness, making
cartilage more brittle and susceptible to mechanical failure.
• AGEs are produced through a non enzymatic reaction
between reducing sugars and free amino groups of proteins
• Age-related changes in size, structure, and sulfation of
aggrecan affect cartilage resiliency and hydration.
Safranin O stained sections of human femoral condyles. Images show young normal (left, age 40), old normal (center,
age 76) and OA donors (right, age 88).

37. The effects of immobilization on the characteristics of
articular cartilage
• With immobilization, there is connective tissue weakening,
articular cartilage degeneration so it not able to withstand large
compressive forces.
• Rapid destruction of articular cartilage occurs with
immobilization because the cartilage is not being bathed by
moving synovial fluid and is thus deprived of its nutritional
supply.
• Vanwanseele et al. showed that cartilage thickness decreases
after spinal cord injury .
• Knee joint immobilization leads to reduced GAG content,
especially from the SZ, with unchanged collagen content.
J. Funct. Morphol. Kinesiol. 2016, ; doi:10.3390/jfmk1020154

38. • Mechanical loading of AC stimulates the metabolism of
chondrocytes and induces the biosynthesis of molecules to
preserve the integrity of the tissue.
• Mechanoreceptors initiates intracellular signaling cascades,
leading to the tissue remodeling process.

39. The effects of exercise on human
articular cartilage
• Enhance synovial movement for cartilage nutrition
• Dynamic (cyclic) loading is beneficial to matrix synthesis.

40. Resistive Exercise for Arthritic Cartilage Health (REACH): A randomized double-blind, sham-exercise controlled
trial
Angela K Lange*1, Benedicte Vanwanseele1, Nasim Foroughi1, Michael K Baker1, Ronald Shnier2, Richard M Smith1 and

41. Special thanks to Dr. Saurabh Sharma sir
for his guidance and assistance