Cartilage

Question 1

Cartilage-Function

Answer 1

increases area of load distribution for joints; attenuates joint contact stress; provides a smooth, wear resistant bearing surface

Question 2

Cartilagen-composition

Answer 2

chondrocytes (maintain organic component),

matrix (collagen type II with GAG; provide structural framework); the scaffolding

collagen fibrils and GAG provide tensile stiffness and strength and resists load

water/salts/glycoproteins; fluid dictates the biomechanical behavior

nearly frictionless b/wjoint surfaces and very limited capacity to repair

Question 3

Cartilage-Mechanical Properties

Answer 3

high tensile stiffness/strength; cannot resist compression well; anisotropic and biphasic

Question 4

Anisotropic

Answer 4

strong in one direction, but not in others; collagen fiber arrangements vary; densities vary throughout tissue; mechanical properties varying between directions/modes of loading

Question 5

Bi-Phasic Material

Answer 5

composed of fluid that is incompressible and a solid is porous and permeable

Question 6

Cartilage-Biomechanical Behavior

Answer 6

contact forces between joint surfaces is huge! this is because of the very small cross sectional area

Question 7

Cartilage-Fluid Components

Answer 7

resists compression; centered toward the near articular surface;

permits exchange between chondrocytes and synovial fluid (gases, nutrients, waste products)

Question 8

Water in Cartilage

Answer 8

fluid leaves and comes back into the capsule and is driven by an electrochemical gradient;

mechanical load creates pressure gradients;ex: sponge that is saturated but leaks when you apply pressure;

Question 9

Creep in Cartilage

Answer 9

applied load balanced by resistive stress within the tissue; creep is caused by fluid leaking out under the load;

an equilibrium occurs when fluid and collagen are balanced

throughout the day, 50% of fluid may be lost until you shift/lay down to allow fluid to fill back up (take off the load)

Question 10

Stress Relaxation in Articular Cartilage

Answer 10

initial increase in stress due to fluid exudation, then stress/relaxation during the displacement maintenance phase as fluid is redistributed

attenuates stress developed within the tissue;

the cartilage compresses, then redistributes the force

Question 11

Proposed mechanisms for Failure of Articular Cartilage

Answer 11

tensile failure (solid gets damaged);

washout of PGs from extracellular matrix from constant inflow and outflow of fluid (causes PGs to disappear, decreasing stiffness)

rapid applications of high loads which don’t allow time for stress-relaxation

Question 12

Fibrillation

Answer 12

splitting of cartilage surface; can extend through the full depth to the subchondralbone

Question 13

Degeneration of Articular Cartilage

Answer 13

progressive deterioration of the tensile properties of solid matrix (cartilage then has too much water because there is more permeability; thus it can’t resist compression as well because there is more outflow of water under load)

as water content increases there is a decreased compressive stiffness

Question 14

Osteoarthritis

Answer 14

increased fluid flow can lead to increased deformation and an increase in the ability to resist loading;

biomechanical changes at muscle/skeletal level may change loading profiles

Question 15

Effects of Aging

Answer 15

progressive deterioration of the tensile properties of solid matrix; structural collagen matrix loosens

increased water content leading to decreased compression stiffness

may be influenced by content stresses magnitudes

accumulation of microtrauma, smaller and fewer GAG molecules, decreased tendon stiffness

Can be mitigated through physical activity and exercise

Question 16

Process of Healing

Answer 16

inflammatory phase (1-10 days)

proliferation phase (3-30 days)

Maturation (remodeling) phase (3-360 days)