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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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