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.