biomechanics and moi of the ankle

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Biomechanics and MOI of the

AnkleImam Subadi,dr, SpRM

Department Physical Medicine and RehabilitationSchool of Medicine Airlangga University

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The primary function ofthe ankle and foot

• Shock absorber and impart thrust to thebody during walking and running

– the foot must be pliable enough to absorb theimpact of millions of contacts throughout alifetime

– the foot must be rigid to be able to withstand

large propulsive thrusts

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Anatomy

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Structural of the bone and joints

Ankle FootBones : tibia, fibula, talusJoints :

– talocrural – Proximal and distal

tibiofibular

Hind foot• bones : calcaneus and talus• joints : talocalcaneal

Midfoot• bones : naviculare, cuboid, cuneiforms• joints : transverse tarsal, calcaneocuboid,distal intertarsal, cuneonavicular,cuboideonavicular, intercuneiform andcuneocuboid complex

Forefoot• bones : metatarsal and phalanges• joints : tarsometatarsal, intermetatarsal,metatarsophalangeal, interphalangeal

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Ankle stability

• Mechanics of the joint• Ligaments• Muscles

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Mechanics of the joint

• The malleoli grip the talus tightly – The grip of the malleoli on trochlea is

strongest during dorsiflexion – The ankle is relatively unstable during plantar

flexion

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Talus• The talus is the

mechanical keystoneat the apex of the foot

• Talus is an extremelyimportant bone for

– Ankle and foot – For the entirely lower

extremity

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LIGAMENTS• Interosseous ligament and membrane• Lateral collateral ligament

– Anterior talofibular –

Calcaneofibular – Posterior talofibular

• Medial collateral ligament – Tibionaviculare – Anterior talotibial – Calcaneotibial – Posterior talotibial

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COLLATERAL LATERAL LIGAMENT

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COLLATERAL MEDIAL LIGAMENT

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LATERAL COLLATERAL LIGAMENTS :

Because of the relative inability ofthe medial malleolus to

adequately block the medial sideof the mortise the majority of anklesprains involve excessive

inversion and subsequent injury tothe lateral collateral ligaments

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THE PRIMARY FUNCTION OF DELTOIDLIGAMENT :

To limit eversion across the TALOCRURAL,SUBTALAR and TALONAVICULAR

SPRAINS are relatively uncommon due tothe ligament strength and the blocking of lateralmalleolus against excessive eversion

DELTOID LIGAMENT :

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Muscles

• The musculotendinous surrounding theankle joint on the medial and lateral sidesplays a small role in stabilizing the joint

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Muscles• Anterior : TA, EHL. EDC• Lateral : PL. PB•

Posterior : GN. SOL• Medial : TP, FHL, FDL

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Kinematics• Uniplanar• One degree freedom of motion•

Axis rotation : – 10 0 to ML axis on frontal plane – 60 to ML axis on horizontal

•

ROM : – Dorsifleksi : 20 degree – Plantar fleksi : 50 degree

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Axis rotation

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Axis rotation

• The axis rotation is inclined slightlysuperior and anterior, from lateral tomedial

– Dorsi flexion is associated with slightabduction and eversion

– Plantar flexion is associated with adductionand inversion

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Walking

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Walking

• Heel strike – foot flat : 0 – 10 0 plantar flexion• Foot flat – heel off : dorsiflexion 10 0

•

heel off –

toe off : 200

plantar flexion

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Kinetics ( static )

• Muscle forcetransmitted through

the Achilles• The line of gravity

pass through the ballof the foot

• The reaction force onthe ankle can becalculated

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KINETICS (dynamics)• The main compressive force across the

ankle during gait was produced bycontraction gastrocnemius and soleus atpush off, about five times body weight

• The contraction pretibial group duringearly stance phase was less than 20percent body weight

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Running cycle

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Running cycle

• Support phase• Flight / recovery phase

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Support phase• Foot strike:

– The foot initially contacts the ground and continuesuntil the plantar surface of the foot is fully plantigradeto the support surface

• Mid-support – The foot is in full contact with the ground and

continues until the heel starts to leave the ground• Takeoff

– The heel starts to leave the ground and continuesuntil the toes are completely free of the supportingsurface

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Flight phase• Follow-through

– The end of take-off until the foot stops any posterioror backward motion

•

Forward swing – The initiation of forward movement of the foot until the

foot reaches the most forward position• Foot descent

– The foot reaches the most forward position until footstrike

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Running phase Joint MotionFoot strike to mid-support

Mid support to take-off

HipKnee

Ankle

Hip

Knee Ankle

45 0 – 20 0 flexion20 0 – 40 0 flexion50 plantar flexion to10 0 dorsiflexion

20 0 flexion to 5 0 extension

40 0 – 15 0 flexion10 0 -20 0 dorsiflexion

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Running phase Joint Motion

Follow through

Forward swing

Foot descent

HipKnee Ankle

HipKnee

Ankle

HipKnee

Ankle

5 –

20 hyperextension15 – 5 flexion20 – 30 plantar flexion

20 – 65 flexion5 – 130 flexion30 plantar flexion – 0

65 – 40 flexion130 – 20 flexion0 – 5 dorsiflexion to 5plantar flexion

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Foot placement during running• The difference between walking and

running is a variation in the base of gait• In walking, the base of gait was

approximately 2 to 4 inches• In running, the base of gait approaches 0.• The reason is an increase in the functional

limb varus of the entire support leg

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FUNGSIONAL LIMB VARUS IN THE

RUNNERS CAN INCREASE VALGUS

STRESS AT THE KNEE AND FOOT

PRONATION

APROXIMATE 10 DEGREE INCREASE INFUNCTIONAL LIMB VARUS IN RUNNINGCOMPARED WITH WALKING

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Muscle activity during running• Ankle :

– The phasic muscle activity of muscles duringrunning is very similar to that during walking

except the magnitude of activity is increasedduring running

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Running Kinetics• The vertical component of the ground

reaction force throughout the stancephase is 125 percent of body weight

• The vertical component of the groundreaction force during running is150 – 200percent greater than during walking