Biomechanics and MOI of the Ankle

8/13/2019 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



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



Anatomy



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



Ankle stability

• Mechanics of the joint• Ligaments• Muscles



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



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



LIGAMENTS• Interosseous ligament and membrane• Lateral collateral ligament

– Anterior talofibular –

Calcaneofibular – Posterior talofibular

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



COLLATERAL LATERAL LIGAMENT



COLLATERAL MEDIAL LIGAMENT



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



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 :



Muscles

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



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

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



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



Axis rotation



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



Walking



Walking

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

•

heel off –

toe off : 200

plantar flexion



Kinetics ( static )

• Muscle forcetransmitted through

the Achilles• The line of gravity

pass through the ballof the foot

• The reaction force onthe ankle can becalculated



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



Running cycle



Running cycle

• Support phase• Flight / recovery phase



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



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



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



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



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



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



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



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

Biomechanics and MOI of the Ankle

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