Biomechanics of Hip Joint

8/12/2019 Biomechanics of Hip Joint

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BIOMECHANICS OF HIP

Dr Siju K M


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Anatomy Ball and socket

synovial joint Head of the

femur articulateswith theacetabulum

Provides a high

degree ofSTABILITY &MOBILITY


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JOINT SURFACES HEAD : >1/2 of sphere Covered by hyaline articular cartilage

ACETABULUM : Lunate articularsurface covered by articular cartilagelatin : vinegar cup

SOURCIL :the area of bone above thesocket which bears the maximum load ofthe BW.. Entirely from the iliac bone


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STABILITY & MOBILITY Depth of acetabulum , narrowing of

mouth by acetabular labrum Tension & strength of ligaments Surrounding muscles Length and obliquity of neck of femur

MOBILITY DUE TO THE LONG NECKWHICH IS NARROWER THAN THEDIAMETER OF THE HEAD


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LIGAMENTS

FIBROUS CAPSULE ILIO FEMORAL LIGAMENT PUBOFEMORAL LIGAMENT ISCHIOFEMORAL LIGAMENT LIG OF HEAD OF FEMUR ACETABULAR LABRUM TRANSVERSE ACETABULAR

LIGAMENT


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CAPSULE PROX:acetabular labrum

including thetransverse acetabularlig

DIST :intertrochanteric line

anteriorly1 cm medial to

intertrochanteric crestposteriorlySynovial membrane

lines the capsule


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Iliofemoral lig (Bieglow) One of the strongest

ligaments of the body Prevents trunk from

falling backwards in

standing posture Inverted Y shaped APEX: lower part of

AIIS

BASE :Intertrochanteric lineas upper oblique andlower vertical bands


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Pubofemoral ligament Support

inferomedially Illiopubic

eminence,obturator crest&membrane toanteroinf part ofcapsule


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Ligament of head of femur

Flat &triangular Fovea capitis to

transverse acet lig &acetabular notch

Transmit arteries to

the head of thefemur


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Acetabular labrum Fibrocartilaginous rim

attached to themargins of the

acetabulum

Holds the head offemur in position

Narrows the mouth ofacetabulum


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Transverse ligament ofacetabulum

Part of theacetabular labrumwhich bridges theacetabular notchconverting it to aforamen which

transmits vesselsto the joint


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The neck of Femur Angulated in relation to the shaft in 2

planes : sagittal & coronal

Neck Shaft angle Anteversion


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Neck shaft angle Angle between the

neck and the shaftin sagittal plane

(viewed from thefront or back)

140 deg at birth 125-135 deg in

adult


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Anteversion Angle between the

neck and shaft inthe coronal plane

(viewed fromabove) Axis of the neck

and thetranscondylar axis


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Anteverted 40 deg at birth 20 deg in adults(15-25)

Ante version : ER of the head offemur in relation to the condyles

Retroversion : IR of the head of thefemur


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Acetabular Direction

Similar rotationaldifferences may alsobe found in theacetabulum

Usually long axis ofthe acetabulum pointsforwards :ANTEVERTED

The Acetabular axis ismore variable

ante version

retroversion


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Flexion 120 degree


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Extension 20 degree


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Abduction 50 degree


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Adduction 30 degree


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ER/IR 45 degree


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Chief muscle access ms

Flexion iliacus,psoas major pectenius,rectusfemoris,sartorius

Extension Gl maximus,hamstringsAdduction Add longus.magnus,brevis pectinius,gracilisAbduction Gl med,min TFL,sartoriusIR TFL,ant fibres of

gl med,min

ER 2 obturators,gamelli , piriformis,glmaximus,sartoriusquadratus femoris


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BIOMECHANICS

Center of mass The center of mass is the unique point at

the center of a distribution of mass inspace that has the property that theweighted position vectors relative to thispoint sum to zero.

Center of mass is the mean location of adistribution of mass in space .


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Center of gravity Center of gravity is the point in a body

around which the resultant torque due togravity forces vanish.
http://en.wikipedia.org/wiki/Resultant_forcehttp://en.wikipedia.org/wiki/Resultant_force


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Subject standing on bothlegs

Little or nomuscular forcesreq to maintain

equilibrium

If support issymmetrical eachhip carries abt31% of the BW


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Trunk+UL 4/6 bwt LL 2/6

Each hip 1/3 Single leg stance 5/6


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Subject standing on one

leg Loaded hip supports the

mass of the head , trunk ,

UL and the other leg CoG lies farther awayfrom the loaded hip

Lever arm of BW is 3times the abductor leverarm


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Centre of gravity S5

BW vector K :(BW-Wt of loading leg)

runs thru S5 ..

medial to the non wtbearing hip


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Muscle balancevector M : Muscleforce to prevent

the left side of thepelvis from fallingdownward

Provided by theabductors actinglaterally to the hip

jt


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Compressive force R

Force acting on the hip Jt

Body Wt lever arm h

Muscular lever arm h

h=3h


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in equilibrium

Kh=Mh M=K (h/h)

Since h/h =3 M=3K

=3 times the body wt

Total force acting on theJoint R = K + M

= K+3K= 4K

4 times the body Wt

Total force acting on the joint when theSubject stands on one leg is almost

Equal to 4 times the body Wt

Coxa vara


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Coxa vara GT is higher than

normal Lenghtens the

abductor lever arm Changes the

direction of theforce M

Decrease in forceM Larger wt bearing

surface

Resultant force R is less thana normal hip


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Coxa valga GT is lower

Shortens theabductor lever arm

Changes thedirection of theforce M

Increase in force M

Resultant force R is more thana normal hip


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Biomechanics in limping PAIN MUSCLE WEAKNESS

Pelvis tilts to the AFFECTED side The body wt lever arm h is shorterin a limping patient.

The abductor lever arm is unaltered


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During the singlesupport phase ofgait the patientdisplaces the trunkto the affected sidebringing the CoGnearer the affected

joint whichrequires lessmuscle force to

balance the BW

Body wt K can be counterbalanced by a smallermuscular force and the resultant R is less


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Biomechanics in limping Limp is defined as any deviation from

the normal effortless gait Clinically we come across 3 types of

limp ANTALGIC SHORT LIMB TRENDELENBERG May be present as single or in

combination


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ANTALGIC GAIT DECREASED STANCE PHASE Bears wt on the affected side for as

short a period as possible Allows the load to remain the normal

hip for a longer time Attempts to protect the hip by tilting

towards the AFFECTED SIDE


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SHORT LIMB GAIT Equal amt of load bearing on either

side NORMAL STANCE PHASE Lurches towards the AFFECTED

SIDE


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TRENDELENBERG GAIT

NORMAL HIPDEPENDS ON

FULCRUM : hip jt LEVER : Neck of

femur

POWER : abductors


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TRENDELENBERG GAIT STANDING ON NORMAL

LEGThe CoG falls towards the

opp hip.The pt tries tomaintain the equilibriumby the power of theabductors which pull theorigin to their insertionthereby raising the opppelvis


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TRENDELENBERG GAIT STANDING ON

AFFECTED LIMB

Opposite pelvisDIPS DOWN due tothe abnormalabductormechanism of thewt bearing hip


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normal

affected


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TRENDELENBERG GAIT disorders causing the pelvis to sag onthe unsupported (opposite) side. This creates an uncompensated

Trendelenberg gait and a positiveTrendelenberg sign. If the upper body leans over the

affected (weak) hip, the pelvic sag iscompensated for and this is a so calledcompensated Trendelenberg gait orsign.


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Causes 1) Suprapelvic.

Costopelvic impingement as in scoliosis 2) Pelvic.

This is due to loss of the fulcrum asin developmental dysplasia of the hip; orof the lever mechanism as in nonunion ofthe femoral neck; or of power as inpoliomyelitis or muscular dystrophy.


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3) Infrapelvic. This is caused by medialdeviation of the mechanical axis of thelower limb .


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GAIT CAUSES STANCEPHASE

PELVICDIP

ANTALGIC Painanywherein the limb

DECREASED AFFECTEDSIDE

SHORTLIMB

Shorteningof anycause

NORMAL AFFECTEDSIDE

TRENDEL-ENBERG

Abn infulcrum ,lever,power

NORMAL NORMALSIDE


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Walking stick Use of a walking stick in the opposite

hand can reduce limping

It lessens the displacement of thetrunk to the affected side during thesingle support period

Exert force C on the stick with a lever arm f


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Exert force on the stick with a lever armForces C & K are vertical & opposite

The moment Cf tends toRotate the pelvis upwardWhile the moment Kh tends To rotate the pelvis down


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The resultant force F = K-C : F acts with a lever arm s which is

smaller than h The force K which normally rotates

the pelvis clockwise with a momentKh is replaced by F

Moment FS is smaller asF


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Stick and Limp Both decrease the moment of force

exerted by the body wt on theloaded hip

Stick :transmit part of the force tothe ground thereby decreasing themuscular force req for balancing

Limping shortens the lever arm byshifting the centre of gravity to theloaded hip


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p

Thank you

Biomechanics of Hip Joint

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