Tissue Mechanics

decreased shear stress =

decreased friction

what is defined as an average force per unit area = pascals P = N/m2

stress

what is defined as deformation from resting length

Strain

which region is when Tissue is at rest & begins to take load, Collagen is uncrimping

toe region

what region is the linear portion, retracts back to original length if removed load (normal)?

elastic region

point at which the tissue yields to the force, change of property (plastic region)

yield point

which region is it when tissue loses its original length, far too stretched due to forces (grade 1 and 2 ligament sprains)

plastic region (microfailure region)

irreversible tissue damage, overloaded (can lead to tearing)

ultimate failure point (macrofailure point)

Size of toe region depends on

collagen arrangement & percentage

During normal activity tendons experience less than

25% of their ultimate stress

Ligaments during normal activity produce about

4% (definitive strain)

what is defined as the tendency of tissue to return to their original shape after being deformed

Elasticity

what is defined as a material’s resistance to flow or ability of a material to dampen forces

Viscosity

Deform under compressive force, capable of returning to original state after removal of force

properties of Viscoelastic Materials

what is defined by constant load, Subject tissue to a constant compressive force over time the tissue will deform and continue to deform over finite length of time. Deformation increases until equilibrium state is reached

creep

what is defined as Constant Deformation, At a fixed length the force required to maintain the length will decrease, Length constant, ↓Force

Stress-Relaxation

Rate-dependent property, Sensitive to speed of loads applied

Strain-Rate Sensitivity

what is defined as Energy Loss during deformation, loading and unloading of a tissue does not result in the same stress-strain curve

Hysteresis

scar tissue is comprised of

Type II & Type III Collagen

■ Decreased strength

■ Random orientation

what is the response to loading (Stretching and lengthening must occur early to generate change)

Fiber orientation becomes more parallel

Decrease tensile strength of ligaments

● Cause disorganization of collagen fibers

○ Fewer cross links

○ More immature collagen

detriments of IMMOBILIZATION

8 weeks of immobilization can cause up to

50% loss of collagen

○ Most critical at bone attachment site