KneeJointAnatomy101
BoneBasics
Therearethreebonesatthekneejoint–femur,tibiaandpatella–commonlyreferredtoasthe
thighbone,shinboneandkneecap.Thefibulaisnottypicallyassociatedwiththekneebecauseitliesoutsidethecapsuleandasassociatedwithanklefunction.
Weneedtoconsidertheosteologicalfeatures(studyofbones)ofthisjointtofullyappreciatethenumerouscomplexmovementsnecessarytoaccomplishflexionandextension.
Thefemoralheadsitsinsidetheacetabulumattheballandsockethipjointwiththeneckconnectinglaterallytothegreatertrochanter.
Distalfeaturesincludetheconvexmedial/lateralcondyles,Intercondylarnotchorpatellargrooveand
adductortubercle.
Thefemurarticulatesatthetibialplateau.Thesecondylesareconcavemedially,convexlaterally,and
dividedbythetibialtubercles,whichfitsnuglyintotheIntercondylarnotchinextension.
Theanatomicalaxisofthefemurboneisdivergentfromthemechanicalaxis,descendingmediallyfromthecenterofthegreatertrochantertotheIntercondylarnotch;conversely,theanatomicaland
mechanicaltibialaxisarenearlyidentical.
Closeexaminationofthetibialandfemoralmedialcondylesofbothfemurandtibiaextendfurtherthantheirrespectivecounterparts,whichcreatesaphysiologicvalgusangleofthekneeapproximating180-
185-degrees.
Diagnosticcriteriaforabnormalfrontalplaneadductionis>185-degrees(GenuValgum)or</=175-degreesabduction(GenuVarum),measuredatthemedial-tibiofemoraljointinextension.
Theanteriororientationofbothlateralcondylesanda25-30-degreecurveonthemedialfemoralcondyleareprobablythemostdistinctfeaturesofthetibiofemoralarticulatingsurfacestructure.
Themedialfemoralcondylearticulatingsurfaceareaislargerandcurvedrelativetothelateralcondyle,
whichisflatter,smallerandmorecircular.Bothstructuresareconvex.
Atthetibialplateau,themedialcondyleisconcaveand50%largerthanthepartiallyconvexlateralcondyle.Thedegreeofposteriorslopevariesbetweencondyles,asdoestheamountofcartilage.
Thepatellaisembeddedwithintheretinaculalayerbetweenthefemurandtibia,attachedsuperiorlytothequadricepstendonandinferiorlytothepatellartendon.Exposedposteriorlytoarticulatewiththe
femoralsulcus,thesurfacecontainsacentralverticalridgeandfacets.
CartilageBasics
Hyalinecartilagecoversalargeportionofthefemoralcondylesandposteriorpatellatoreducepatellofemoralarticularfriction.
Fibrocartilagenousmenisciatthetibialplateaucreateasemi-flexiblehousingthatcompensatetibiofemoralobliquity.
Menisciattachedtothesurfaceofthetibialplateauimprovecongruence,pressuredistributionandarticulationatthetibiofemoraljoint.
Fixedtothetibiaatthehornsandcoronaryligamentstheyarejoinedanteriorlybythetransverse
ligament.
Thelateralmeniscusformsanearlycompletecircleandcoversamajorityofthetibialcondyle’ssurface,withanteriorandposteriorhorns(typically)blendingintotheattachmentoftheACL.Thereisno
attachmentbetweenthelateralmeniscusandthelateralcollateralligament,providingincreasedmobilityincomparisontothemedialmeniscus.
Thec-shapedmedialmeniscusislarger,butcoverssignificantlylesssurfaceareathenthelateral
meniscus.AnteriorfibersoftheACLblendwiththetransverseligamentandanteriorhornofthemedialmeniscus.Andcapsularattachmentsjointothedeepmedialcollateralligamentdirectlyandpatellavia
thepatellomeniscalligaments.
LigamentBasics
Ligamentscreatepassiveresistancetofacilitateoptimalkneefunctionandstability.
TibiofemoralLigaments:
ThedeepanteriorandposteriorcruciateareconsideredIntracapsularandextrasynovialbecausetheyexistinsidethejointcapsulebutoutsidethesynovialmembrane,crossinganterior/posterior&
posterior/anteriorbetweenfemurandtibia.
Themedial(tibial)collateralligamentcontainssuperficial(extracapsular)anddeep(capsular)components,betweenfemurandtibia,andthelateral(fibular)ligamentispurelyextracapsular,
connectingfemurtofibula.
PatellofemoralLigaments
Patellarmovementisinitiatedbythequadricepsandguidedbythemedial/lateraltibialandfemoralligaments.
KneeJointCapsule
Consistentwithothersynovialjoints,thekneeexistswithinacapsulemadeofconnectivetissueandbone.
Theouterlayerconsistsofafibrousmembranewithopeningsatthepatellaforthesuprapatellarbursaandlateraltibialcondyleforpoplitealmuscle,inseparablewithnumeroussupportingcapsularligaments.
Theinner-membranesecretessynovialfluid(andnutrients)toreducefrictionbetweenjointsurfaces
Bursaandfat-padsareinterspersedbetweenmuscles,tendonsandbonesasbuffersforfrictionandpressure.
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MuscleBasics
Anteriormusclesofkneejointaremonoarticulating(articulate/crossone-joint)orbiarticulating(articulate/crosstwo-joints).
Musclesindirectlyinfluencingthekneeareindicatedwithbluearrows.
Posteriormusclesofthekneejointarealsomono-andbiarticulating.
Musclesindirectlyimpactingthekneeareindicatedwithbluearrows.