Exam 1: Tissue Mechanics Flashcards by Marissa Kline

Primary tissue components

Collagen
Elastin
Ground substance
Water

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Collagen has continuous _____ through growth to maturity

Metabolic turnover

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At maturity the collagen fibers become more

Stable

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Collagen chains are synthesized ans secreted by

Fibroblasts

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Collagen molecules align in the ____ in a ____ arrangement

Extracellular matrix; parallel

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Collagen can stretch to ____ its original length

110%

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Ligaments change under tension

Inc ligament strength

Inc ligament size

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Increased lig size is accomplished by

Inc # of collagen fibrils
Inc collagen fibril diameter
Inc cross-linking
Inc collagen fibril packing density

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Immobilization causes these degenerative ligament (collagen) changes

Dec diameter
Dec density
Dec fibril #
Dec overall mass
Dec metabolism

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Immobilization at ligament-bone junction changes

Inc osteoclast activity
Bone resorption
Disruption of diffusion

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Immobilization increases the risk of ____ at the ligament-bone junction

Avulsion injuries

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Elastin can stretch to ____ its original length

150%

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Age-related changes to elastin

Lose resiliency
Fragmentation/fraying
Calcification
Inc cross-links

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Contents of Ground Substance

GAGs
Plasma proteins
Small proteins
Water

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GAGs, plasma proteins and small proteins all attract

Water

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Water = _____% of total CT content

60-70%

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4 major GAGs

Hyaluronic acid
Chondroitin-4-sulfate
Chondroitin-6-sulfate
Dermatan sulfate

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_____ is found in high concentration within GAGs

Glucosamine

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Hyaluronic acid + water is a powerful _____

Lubricant

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Water maintains _____ between collagen fibers which allows ____ and prevents _____

Critical distance

Allows free gliding; prevents excessive cross-linking

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Mechanical forces play an important role in ______ of tissue as well as ______

Development, maintenance, remodeling

Damage and disease

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Tissue biomechanics is study of how different parts of human body _____

React to external forces

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When a load produces forces that push material together

Compression

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When a structure is stretched longitudinally

Tension

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Forces acting parallel to each other in opposite directions

Shear

Forces twisting/rotating in opposite directions about long axis

Torsion

Combination of tensile and compressive loads

Bending

Behavior of compressed structures depends on

Its length; how far or long load is applied

Nearly constant compressive forces are transmitted to

Vertebral body and IVD

Examples of compression injuries

Bruises Crushing Compression fractures Pinching

Compression fractures happen a lot in _____ because there is _____

Older female patients Too much force/too little bone density

Tension is a _____ force

Stretching or pulling

Tension elements of the body are ___

Soft tissues

Tensile forces occur in the IVD during ____ movements

Rotational

Examples of tension injuries

Sprain/strain Avulsion fractures Nerve traction injuries

_____ bones are most at risk for fracture due to shear forces

Cancellous

In the spine ____ resist shear forces

Facet joints and annulus fibrosus fibers

Examples of shear injuries

Brain injuries ACL/PCL injuries Blisters Spine injuries

Excessive torsion can result in failure of:

Facet joint Part interarticularis Capsular tears Circumferential tear of annulus

____ fractures of long bones are another example of torsional load failure

Spiral

_____ is a combination of compression and tension

Bending

Tissue responses in response to force

1. Deformation 2. Growth/remodeling 3. Failure

Local shape change due to applied forces

Deformation

Extent of deformation depends on

1. Material properties 2. Size/shape 3. Environmental 4. Force (magnitude, direction, duration)

External force acting to deform a material

Stress

Stress measures the ___ of the force

Intensity

Magnitude of deformation as result of applied stress/loading

Strain

Strain is a measure of _____

Degree of deformation

Stress is _____, strain is _____

What is done to object; how object responds

Strain is ____ to stress

Proportional

In addition to strain in direction of applied stress, there is also strain ____ to direction of loading

Perpendicular (orthogonal)

Maximum stress a tissue can withstand without permanent deformation

Strength

Yield strength

Stress at yield point of a material beyond which permanent deformation will occur

Ultimate strength

Maximal stress a material can withstand prior to initiation of failure

Failure strength

Stress where material actually breaks/ruptures

Ductility represents how much ____ the structure can sustain _____

Force and deformation; before it fails

Ductile tissues fail at ____ but can withstand ____

Low stress; large strain

Brittle tissues can withstand ___ but fail with ___

High stress; low strain

Total energy required to cause material failure

Toughness

Toughness is estimated by observing

Total area under stress/strain curve

Bone = more ___, very ____

Brittle; strong

Overall toughness of bone =

Low

Tendon = moderate for both

Strength and ductility

Overall toughness of tendon =

High

Ligament = more ___ and lower ____

Pliant; strength

Overall toughness of a ligament =

Moderate

Ability to return to original shape when load is removed

Elasticity

Plastic region

Response of material after yield point Deformation persists after stress removal

Elastic stretch represents _____ behavior

Spring-like

Property of materials to resist loads that produce shear/tensile forces

Viscosity

Viscous stretch refers to

Putty-like behavior Deformation by tensile stress remains after stress is removed

When material shows both properties of viscosity and elasticity

Viscoelasticity

Viscoelasticity is affected by both ____ and ____ it is subjected to constant load

Rate of loading; length of time

Viscoelastic structures show time dependent loading characteristics:

Creep Relaxation Hysteresis

Continued deformation over time when constantly loaded

Creep

Creep in tissue occurs due to

Expulsion of water

Eventual decrease in stress that occurs as fluid is no longer exuded

Relaxation

Energy loss by viscoelastic materials when subjected to loading/unloading

Hysteresis

The larger the load the ___ the hysteresis

Greater

What does it mean when hysteresis decreases

Less capacity to absorb the shock energy

What can happen as a result of decreased hysteresis

Inc deformation | Molecular disruption

Compliant tendons can absorb elastic energy more easily they have ___ hysteresis which could be related to ___ injury risk

Dec; dec

In general, weight training will ____ stiffness, while flexibility exercises will ___ compliance

Increase; increase

_____ hysteresis is advantageous

Low

Hysteresis is dependent on

Rate of loading/unloading

Dynamic activities (plyo/ballistics) can increase pliability of MTC and thereby

Dec hysteresis (dec injury risk)

Toe region

Normal range of motion

Toe region is the little force required to remove the

Crimping/slack in the tissue

After toe region, tissue

Resists elongation much more strongly

Micro-failure occurs after

Taking out slack in soft tissue

During micro-failure the tissue is still _____

Elastic

Example of micro-failure

Grade 1 sprain (small amount of damage)

Yield stress is the stress when

Plastic deformation starts

In yield stress, when the force is taken off

It will stay deformed

Plastic deformation example

Grade 2 sprain

Example of tissue rupture

Grade 3 sprain