TISSUE MECHANICS Collagen - PowerPoint Presentation

Slide1

TISSUE MECHANICS

Slide2

Collagen

Collagen based structures are made up of the following building blocks:water, collagen fibers, ground substance and fibroblasts.It is the main structural

fibrous component of ligaments, tendons, joint capsules and

fascia

All collagen is designed to resist tensile loads

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Collagen

Plays a major supportive role in structures that are exposed to tension and compressionBuilt into a matrix-like structure that allows the collagen fibers to be under tension while the tissue itself is under

compression

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Collagen Fibers

Form bundles of various sizesIn

unstretched

tissue they have a waveform that straightens out under

stressThe fibers run

in a crossing, spiraling and intertwining

pattern vs. running parallel to each

other

M

akes

relative big changes in shape possible, without causing undue stress on the collagen fibers

itself

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Collagen Fibers

The collagen fibers are made up of collagen fibrils and these in turn consist of fine micro fibrils, which are aggregates of tropocollagen molecules. At every level of organization within collagen assemblies there are cross-links between adjacent longitudinal elements.

The elements of the ground substance are responsible for these cross-links.

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Fibroblasts

Fibroblasts synthesize most of the extra cellular matrix of connective tissue and accordingly have all the features typical of cells engaged in the synthesis of protein. They

are usually adherent to the fibers that they lay down.

They are also very active during wound repair, laying down granulation tissue.

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Ground Substance

The ground substance is made up of 2 macro-molecular complexes:Glycoproteins and Proteoglycans

Proteoglycans

are stretched out protein parts with polysaccharide links, called glycosaminoglycans (GAGs).

Proteoglycans

are connected with each other by

hyaluronic

acid molecules, and are stabilized into a super molecular complex by the

glycoproteins

.

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Ground Substance

The ground substance functions as a lubricant between the collagen fibers, but it also functions as the initial groundwork upon which new collagen fibers are laid out in the proper direction.

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GAGs

Holds water, acts as a lubricant and a buffer for the fibrous elementsT

he primary component of connective tissue that resists compression

.

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Metabolic Turn Over Rate

The mobility of the ground substance decreases with age, immobility, atrophy of muscles, or trauma, which is related to dehydration.The metabolic turn over rate of the ground substance is 2-10 days. The metabolic turn over time for collagen fibers is approximately 300 days.

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Stress/Strain Curve

Diagrams the process of connective tissue extensibility. C

ollagen

based extensibility is due

to:Stretching of the collagen fibers (6-8% before failure

)

Uncrimping

of collagen

fibers

Glide

between fibers and fibrils

Water content redistribution

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Toe Region

“A”: structure settles, slack is being picked up.

“

Uncrimping” of the collagen fibers occursMost functional

activities of

connective

tissue take place in this region.

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Elastic Region

“B”: the stress in the tissue is directly proportional to the

strain.

Deformation in

this region is completely reversible.

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Elastic Limit

“C”: the end of the elastic region

Critical

junction, as the tissue starts to become damaged as the result of being

loaded.

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Plastic Region

“D”: the tissue begins to lengthen at a rate disproportionate to the stress.

This

is usually a permanent deformation

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Failure Point

“G”: a sudden decrease in the stress occurs while the strain continues to

rise

T

he substance of the material has started to fail.A force

of 5-15 kg/mm2

is required to

tear a collagen fiber.

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Effects of Immobilization on Connective Tissue

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Collagen Fibers

The amount of collagen fibers does not increase as a result of immobilizationHowever, new collagen fibers are not laid down along the lines of stress, which can contribute to the restricted ROM.

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Ground Substance

The amount of water, hyaluronic acid and GAG’s decreases

significantly: decreased lubrication between collagen fibers

The

collagen fiber interspace also decreases, which can lead to cross linking of fiber

intersections.

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Intermolecular Cross Linking

Research has shown that during periods of immobilization that there is up to a 30% - 40% reduction in the level of GAGs within the ground substance, precipitating a loss of 4% - 5% of the water content causing ground substance dehydration. (Akeson, Woo, & Amiel

)

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Rate of Tissue Healing

50% of healing is in the first 2 weeks80% of healing is in the first 6 weeks100% of healing has occurred by the 12th week

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Stage of The Condition

Immediate: few minutes immediately following the injury. First aid by the patient is most effective.Acute: condition

is worsening. Goal of treatment is to limit worsening.

Sub

acute: commencing to improve. Status is fragile.

Settled

: stabilized

. Corrective treatments are well tolerated.

Chronic

: primary

healing has finished. Behaviors and adaptation.

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Reactivity (irritability) of condition

High reactivitypain

before restriction

Moderate

reactivitypain with restriction

Low

reactivity

no

pain at restriction

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Factors to Consider with Soft Tissue Injury

Extent of trauma

Degree

of

inflammationDegree of muscle guarding

Amount

of collagen laid

down

Direction

of collagen laid

down

Extent of collagen remodeling

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Factors that Influence Remodeling

MotionBlood supply and oxygen supply to the injured tissueVitamin CAdequate protein intake

Anti inflammatory drugs

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Effects of Therapeutic Exercise

New collagen and proteoglycans synthesizedRealignment and lengthening of old fibersIncreased

inter-fiber

distance

Increased lubricationAlignment of new collagen fibers in relation to the lines of stressCellular modulation (release of enzymes causing breakdown of old connective

tissue

Results in INCREASED TISSUE ELASTICITY

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Scar Tissue Formation

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Scar Tissue

Remains adaptable up to 8-10 weeks post trauma. Maximum strength will be reached at 1 year post injury