dutton chapter04 the response of biological tissue to stress

8/18/2019 Dutton Chapter04 the Response of Biological Tissue to Stress

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Chapter 4Chapter 4

The Response of Biological The Response of Biological

Tissue to Stress Tissue to Stress


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OverviewOverview

A wide range of external and internalA wide range of external and internal

forces are either generated orforces are either generated or

resisted by the human body duringresisted by the human body duringthe course of daily activitiesthe course of daily activities

Biological tissues must demonstrateBiological tissues must demonstrate

the ability to withstand excessive orthe ability to withstand excessive orrepetitive stresses if musculoskeletalrepetitive stresses if musculoskeletal

health is to be maintainedhealth is to be maintained


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StressStress

The capacity of a tissue to withstand The capacity of a tissue to withstand

stress is dependent on a number ofstress is dependent on a number of

factors:factors:– AgeAge– The proteoglycan and collagen content of The proteoglycan and collagen content of

the tissuethe tissue

– The ability of the tissue to undergo adaptive The ability of the tissue to undergo adaptivechangechange

– The speed at which the adaptive change The speed at which the adaptive change

must occurmust occur


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TerminologyTerminology

inetics ! the study of forces that ariseinetics ! the study of forces that arise

as motions changeas motions change

"ass ! the #uantity of matter"ass ! the #uantity of mattercomposing a bodycomposing a body

$nertia ! the resistance to action or to$nertia ! the resistance to action or to

changechange

%orce ! a vector #uantity& with%orce ! a vector #uantity& with

magnitude& direction and point ofmagnitude& direction and point of

application to a bodyapplication to a body


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TerminologyTerminology

'oad ! the type of force applied'oad ! the type of force applied Stress ! the force per unit area thatStress ! the force per unit area that

develops on the cross section of adevelops on the cross section of astructure in response to an externallystructure in response to an externallyapplied loadapplied load

Strain ! the deformation that developsStrain ! the deformation that developswithin a structure in response towithin a structure in response to

externally applied loadsexternally applied loads (ysteresis ! the di)erence in the(ysteresis ! the di)erence in the

behavior of a tissue when it is beingbehavior of a tissue when it is beingloaded versus unloadedloaded versus unloaded


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Load-deformationLoad-deformation

curvecurve The load!deformation curve& or The load!deformation curve& or

stress!strain curve& of a structurestress!strain curve& of a structure

depicts the relationship betweendepicts the relationship betweenthe amount of force applied to athe amount of force applied to a

structure and the structure*sstructure and the structure*s

response in terms of deformationresponse in terms of deformationor accelerationor acceleration


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Load-deformationLoad-deformation

curvecurve The shape and position of the The shape and position of the

load!deformation curve dependsload!deformation curve depends

on a number of factors:on a number of factors:– Sti)nessSti)ness

– +iscoelasticity+iscoelasticity

– AgeAge– ,xercise,xercise


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Musculoskeletal stressMusculoskeletal stress

"acrotrauma ! an acute stress"acrotrauma ! an acute stress

0loading1 that occurs when a single0loading1 that occurs when a single

force is large enough to cause in2uryforce is large enough to cause in2uryof biological tissuesof biological tissues

"icrotrauma ! a repetitive stress that"icrotrauma ! a repetitive stress that

in of itself is insu3cient to damagein of itself is insu3cient to damage

the tissue& causes in2ury whenthe tissue& causes in2ury when

repeated over a period of timerepeated over a period of time


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CollagenCollagen

-ollagen 4bers have a wavy or folded-ollagen 4bers have a wavy or foldedappearance at rest 0slack1appearance at rest 0slack1

5hen a force lengthens the collagen5hen a force lengthens the collagen4bers this slack is taken up4bers this slack is taken up This slack is called the tissue*s This slack is called the tissue*s crimpcrimp -rimp is di)erent for each type of-rimp is di)erent for each type of

connective tissue and this providesconnective tissue and this provideseach of these tissues with di)erenteach of these tissues with di)erentviscoelastic propertiesviscoelastic properties


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Articular cartilageArticular cartilage

Articular cartilage is a viscoelasticArticular cartilage is a viscoelastic

structure with a very high tensilestructure with a very high tensile

strength and is resistant tostrength and is resistant tocompressive and shearing forcescompressive and shearing forces

Articular cartilage has the abilityArticular cartilage has the ability

to undergo large deformationsto undergo large deformationswhile still being able to return towhile still being able to return to

its original shape and dimensionits original shape and dimension


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Articular cartilageArticular cartilage

6amage to articular cartilage may6amage to articular cartilage may

result from microtraumaresult from microtrauma

0degeneration1& macrotrauma& or0degeneration1& macrotrauma& oran in/ammatory processan in/ammatory process

– 6egeneration: osteoarthritis6egeneration: osteoarthritis

7rimary and secondary7rimary and secondary– $n/ammation: Rheumatoid arthritis$n/ammation: Rheumatoid arthritis


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LigamentLigament

%ibrous bands of dense%ibrous bands of dense

connective tissue that connectconnective tissue that connect

bone to bone and which behavebone to bone and which behaveas a viscoelastic structures whenas a viscoelastic structures when

exposed to stressexposed to stress

'igament in2uries are called'igament in2uries are calledsprainssprains


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TendonTendon

-onnects muscle to bone-onnects muscle to bone

The causes of a tendon in2ury The causes of a tendon in2ury

center around microtrauma to thecenter around microtrauma to thetendon tissue due to repetitivetendon tissue due to repetitive

mechanical loading from externalmechanical loading from external

factors& or macrotraumafactors& or macrotrauma


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TendinitisTendinitis

The term The term tendinitistendinitis implies animplies an

in/ammatory reaction to a tendonin/ammatory reaction to a tendon

in2ury ! a microscopic tearing andin2ury ! a microscopic tearing andin/ammation of the tendonin/ammation of the tendon

tissue& commonly resulting fromtissue& commonly resulting from

tissue fatigue rather than directtissue fatigue rather than directtraumatrauma


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TenosynovitisTenosynovitis

Tenosynovitis/tenovaginitis, peritendinitis,Tenosynovitis/tenovaginitis, peritendinitis,

and paratenonitis, indicate anand paratenonitis, indicate an

inflammatory disorder of tissuesinflammatory disorder of tissuessurrounding the tendon such as the tendonsurrounding the tendon such as the tendon

sheath – usually the result of a repetitivesheath – usually the result of a repetitive

friction of the tendon and its sheathfriction of the tendon and its sheath


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TendinosisTendinosis

The term The term tendinosistendinosis refers to arefers to a

degenerative process of thedegenerative process of the

tendon.tendon. -haracteri8ed by the presence of-haracteri8ed by the presence of

dense populations of 4broblasts&dense populations of 4broblasts&

vascular hyperplasia& andvascular hyperplasia& anddisorgani8ed collagendisorgani8ed collagen


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oneone

Wolf’s lawWolf’s law ! forces applied to! forces applied to

bone& including musclebone& including muscle

contractions and weight bearingcontractions and weight bearingcan alter bone the internal andcan alter bone the internal and

external con4guration of boneexternal con4guration of bone

through adaptation to thesethrough adaptation to thesestressesstresses


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oneone

$f the adaptations of bone to stress do$f the adaptations of bone to stress do

not occur fast enough& the bone isnot occur fast enough& the bone is

resorbed faster than it is replaced& andresorbed faster than it is replaced& and

bone strength is compromisedbone strength is compromised

-auses of decreased adaptation include:-auses of decreased adaptation include:

– An increase in the applied loadAn increase in the applied load

– An increase in the number of applied stressesAn increase in the number of applied stresses– A decrease in the si8e of the surface areaA decrease in the si8e of the surface area

over which the load is appliedover which the load is applied


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Muscle tissueMuscle tissue

"uscle in2ury can result from:"uscle in2ury can result from:

– ,xcessive strain,xcessive strain

– ,xcessive tension,xcessive tension– -ontusions-ontusions

– 'acerations'acerations

– Thermal stress Thermal stress

– "yotoxic agents 0local anesthetics&"yotoxic agents 0local anesthetics&excessive use of corticosteroids& snake andexcessive use of corticosteroids& snake and

bee venoms1bee venoms1


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!ematoma!ematoma

-ontusion to a muscle belly-ontusion to a muscle belly Two types: Two types:

– $ntramuscular: associated with a muscle$ntramuscular: associated with a musclestrain or bruise. The si8e of thestrain or bruise. The si8e of thehematoma is limited by the musclehematoma is limited by the musclefasciafascia

– $ntermuscular. This type of hematoma$ntermuscular. This type of hematomadevelops if the muscle fascia is ruptureddevelops if the muscle fascia is rupturedand the extravasated blood spreads intoand the extravasated blood spreads intothe interfascial and interstitial spacesthe interfascial and interstitial spaces


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"mmo#ili$ation"mmo#ili$ation

-ontinuous immobili8ation of-ontinuous immobili8ation of

connective and skeletal muscleconnective and skeletal muscle

tissues can cause sometissues can cause someundesirable conse#uences to theundesirable conse#uences to the

tissues of the musculoskeletaltissues of the musculoskeletal

systemsystem


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"mmo#ili$ation"mmo#ili$ation

The undesirable conse#uences The undesirable conse#uences

include:include:

– -artilage degeneration-artilage degeneration– A decrease in the mechanical andA decrease in the mechanical and

structural properties of ligamentsstructural properties of ligaments

– A decrease in bone densityA decrease in bone density– 5eakness or atrophy of muscles5eakness or atrophy of muscles

dutton chapter04 the response of biological tissue to stress

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