Amrita Knee Biomech

7/31/2019 Amrita Knee Biomech

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KNEE BIOMECHANICS

by

amrita..


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Objectives..

To discuss the following about THE KNEE JOINT

AnatomyOsteokinematicsArthrokinematicsStabilizers (static & dynamic)Pathomechanics


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Introduction

Most complex joint of the body

Designed for maximum mobility.. & Stability..

During swing- shortens functional length of l/l

During stance- remains slightly flexed allowing

shock absorption.., conservation of energy..,&

transmission of forces.. through lower limb


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Knee is composed of 2 joints


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Bony structure


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Attachments of menisci


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Clinical relevance

reduced mobility of MM

more incidence of injury

MM covers less surface area of medial condyle of

tibia increased compressive forces at medial

Tib-fimoral jt articular cartilage destruction


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Meniscal injury (at the periphery & horns)

Injury to mechanoceptors and nociceptors

pain & proprioceptive deficits

Thus, meniscectomy doubles articular cartilage

stresses at tibial & femoral art.surface

degenerative changes at Tib- fem jt


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Joint capsule

Enclose TF and PF joint

Lax and large

2 layers - exterior (sup) fibrous layer

- interior (thin) synovial memb.

Innervated by nociceptors and mechanoceptors

Synovial membrane secretes and absorbs synovial fluid

lubricates jt. & nourish avascular structures (menisci)


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Clinical relevance Incomplete resorption of synovial septa

appears as folds in synovial membrane

PLICA(Types superior, middle, inferior )

Plica moves back & forth over femoral

condyle

occasionaly, plica gets irritated and inflamed

pain & effusion( PATELLAR PLICA SYNDROME)


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FOR Knee jt swelling

Resting position of knee jt- 15-30 deg

reduces tension in capsule & increase pt comfort

Thus this position is indicated in knee jt. swelling


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LIGAMENTS


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lateral (fibular)

medial (tibial)

Collateral Ligaments

Prevents abductionand adductionmovement of the knee


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Cruciate ligament

Anterior Cruciate ligament Posterior Cruciate ligament


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ACL

Prevents anterior translation of tibia

Limits internal tibial rotation (at 10-15 deg. of flexion)

Acts as secondary restrain against varus and valgus motion atknee

ACL is lax at about 30 deg. of knee flexion

Divided in 2 bands AMB & PLB

PLB is taut in full extension

AMB becomes taut as flexion increases


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Anterior Cruciate (ACL)

ACL


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PCL

Restrains posterior displacement of tibia

Limits internal tibial rotation (at 90 deg. knee

flex.)

PCL cross sectional area > ACL

so less susceptible to injury


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PCL

shorter and stronger than ACL

PCL


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FE

MUR

TI

BI A

PATELLA

The ACL prevents thefemur from sliding

posteriorly on thetibia or the tibia fromsliding anteriorly onthe femur

The PCL prevents thefemur from sliding

anteriorly on the tibiaor the tibia fromsliding posteriorly onthe femur


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Clinical relevance

Anterior tibial translation caused by quads

and prevented by ACL

In ACL injury, Hams shares the role of ACL in

resisting Ant. Translation of tibia and prevents

strain on ACL -> thus ACL rehab should hams

dominant exercises


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Posterior tibial translation - caused by hams

and prevented by PCL

In PCL injury, popliteus muscle shares the role

of PCL in resisting Post. Tibial translation.


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Bursae of the Knee


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Clinical relevance

Trauma to front knee like prolonged kneeling

positions->

inflammation of infrapatellar and prepatellar

bursa ->

pain and effusion


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Osteokinematics

3 degrees of freedom

1. Flexion/ extension (medio lateral axis, sagital

plane)

2. Abduction / adduction (AP axis, frontal plane)

3. Medial rotation / lateral rotation (vertical

axis, horizontal plane)


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Degree of ROM

According to AAOS , chicago (1965), Flexion 135 o

Extension

5-10 o During 90 o knee flexion,

lat rotation 0-20 o

Med rotation 0-15 o


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NWB WB


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ArthokinematicsIn weight bearing


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Screw home mechanism

Automatic rotation of the tibia externally (approx. 10

degrees) during the last 20 degrees of knee extension.

Forms a close-packed position for the knee joint

During knee flexion, tibia rotates internally(unlocking of

knee) .

Driven by 3 factors


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Patellofemoral joint


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Normal length of patellar tendon =patellar height: 1:1 ratio

Patellar Contact Areas


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Motions of patella


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Rotation of patella follows rotation of tibia


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Frontal Plane Stability


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Q-angle

Knee in extension

Normal - males - 13 degrees

Normal - females - 18 degrees

Knee in 90 degrees flexion

Both genders - 8 degrees

At i l Q l


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Atypical Q-angles

Bow-leg knock-knees


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Posture & WB Forces

The mechanical axis of TF

joint is the weight bearing

line from the center of

femoral head to superior

talus center

Allows WB in stance of the

medial = lateral

Tibiofemoral compartments


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Increase in valgus results:

Compression overload to

the lateral Tibiofemoral

compartment

Distraction overload tomedial Tibiofemoral

compartment

Posture & WB Forces


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Decrease in valgus results

Compression overload to

the medial Tibiofemoral

compartment

Distraction overload to

lateral Tibiofemoral

compartment

Posture & WB Forces


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Movements of the knee

Flexion Hamstrings (SM,ST,BF)

assisted by: gracilis sartorius popliteus gastrocnemius


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Gracilis

Sartorious


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Popliteus


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Gastrocnemius


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Muscle Pull


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Movements of the knee

Extension quadriceps:

rectus femoris vastus lateralis vastus medialis vastus intermedius


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Rectus femoris


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Vastus lateralis

Vastus intermediate

Vastus medialis


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Muscle Pull


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Amrita Knee Biomech