Bio Mechanics of Knee2

8/14/2019 Bio Mechanics of Knee2

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BIOMECHANICS OF KNEE JOINT

, , ,IRTA Z A K A Z M I D ep artm en t of Ph ysioth erap y H FHR a w a lp in d i


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TIBIOFEMORAL Joint

Double Condyloid jointThree degrees of freedom of angular

motion


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FLEXION EXTENSION

Occur inSAGITTALPLANE

Around acorornalAxis

Trough theepicondylesof the distalfemur


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MEDIAL LATERALROTATION

Occur inTRANSVERSE PLANE

About aLongitudinalAxis

Trough theLateral sideof themedial tibialcondye


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ABDUCTION &ADDUCTION

Occur inFRONTALPLANE

Aroundanteroposterior axis

Trough theepicondylesof the distalfemur


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Anatomic axis of femur

-obliqueDirected inferiorly & medially from

its distal end.


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Anatomic axis of tibia

Directed almost vertically


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The femoral and tibiallongitudinal axes

The femoral and tibial longitudinalaxes normally form an angle

medially at knee joint of 180 to185; that femur is angled upto 5 offvertical, creating slight physiologic(normal) valgus angle at the knee.


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If the medialtibiofemoralangle is greater

than 185, anabnormalcondition called

Genu valgumexists.


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If medial tibiofemoralangle is less than175 or less, the

resulting abnormalityis called genu varum.

Each condition altersthe compressive andtensile stresses onthe medial andlateral

compartments of the


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Each condition alters thecompressive and tensile stresses

on the medial and lateralcompartments of the knee


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Method to measure thetibiofemoral alignment

By drawing a line from thecenter of the femoralhead to the center ofthe head of the talus

This line represents themechanical axis , orweight bearing line , ofthe lower extremity.

IN NORMALLY align knee ,

it will pass through thecenter of the jointbetween theintercondylar tubercles.


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Weight Line

Can be used as a simplification ofthe ground reaction force as it

travels up the lower extremity.


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IN CASE OF UNILATERALSTANCE

Once unilateral stance is adopted ordynamic forces are applied or

dynamic forces are applied to thejoint, compartmental loading isaltered.


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IN CASE OF UNILATERALSTANCE

The weight bearingline must shiftmedially accross theknee to account for

the now smallerborder of supportbelow the center ofmass

This shift increased

the compressiveforces on the medialcompartment.

ABNORMALcompartmental

loading may also becaused b frontal


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GENU VALGUM.

Shifts the weightbearing line onto thelateral comparmtent

Increasing the lateralcompressive force

While increasing thetensile forces on the

medial structure


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GENU VARUM

Shifts the weightbearing line ontothe medial

comparmtent Increasing the

medial

compressive force While increasing the

tensile forces onthe lateral

structure


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RESULT

Presence of Genu varum or valgumcreates a constant overload of the

lateral or medial articularcartilage , respectively, which mayresult in damage to the cartilageand the development of frontal

plane laxity.GENU VARUM......m y

ontr ut to tb

pro r ss on o

m l omp rtm nt

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Bio Mechanics of Knee2