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1、Chapter391SonographicandpowerDopplernormalanatomy3.1CartilageCartilageisagreatlyspecializedtypeofconnectivetissue,mainlycomposedofwater(70-80%bywetweight).Itisavascularandaneural.Thesolidcomponentofcartilageisformedofcells(chondro-cytes)thatarescatteredinafirmgel-like
2、substance(extracellularmatrix)consistingofcollagenandproteoglycans.Collagenformsanetworkoffibrils,whichresiststheswellingpressuregeneratedbytheproteoglycans.Inthemusculoskeletalsystemtherearetwotypesofcartilage:hyalineandfibro-cartilage.Comparedtohyaline,fibrocartilag
3、econtainsmorecollagenandismoreresistantattensilestrength.Fibrocartilageisfoundinintervertebraldisks,symphyses,glenoidlabra,menisci,theroundligamentofthefemur,andatsitesconnectingtendonsorligamentstobones.Hyalinecartilageisthemostcommonvarietyofcartilage.Itisfoundincos
4、talcartilage,epiphysealplatesandcoveringbonesinjoints(articularcartilage).Thefreesurfacesofmosthyalinecartilage(butnotarticularcartilage)arecoveredbyalayeroffibrousconnectivetissue(perichondrium).Hyalinecartilagestructureisnotuniform(Fig.3.1).Instead,itisstratifiedand
5、dividedintofourzones:superficial,middle,deep,andcalcified.Thesuperficialzone,alsocalledtangentialzone,isconsideredthearticularsurfaceandischaracterizedbyflattenedchondrocytes,relativelylowquantitiesofproteoglycan,andnumerousthickerfibrilsarrangedparalleltothearticular
6、surfaceinordertoresisttension.Inarticularcartilagethislayeractsasabarrierbecausethereisnoperichondrium.Themiddlezone,ortransitionalzone,incontrast,hasroundchondrocytes,thehighestlevelofproteoglycanamongthefourzones,andaran-domarrangementofcollagen.Thedeep(radiatezone)
7、isthethickestzone,characterizedbycollagenfibrilsthatareperpendiculartotheunderlyingbone,actingasananchortoprohibitseparationofzonesandinordertoresistattorsionalandcompressivemechanicalstrength.Columnsofchondrocytesarearrayedalongtheaxisoffib-rilorientation.Thezoneofca
8、lcifiedcartilageispartlymineralized,andactsasthetransitionbetweencartilageandtheunderlyingsub-chondralbone.Aboundarypoint(ti
