IVD.pptx

INTERVERTEBRAL DISC (IVD) ANATOMY FUNCTION BIOMECHANICAL PROPERTIES ANATOMY • IVDS MAKE UP 20-33% OF THE ENTIRE HEIGHT OF THE SPINAL COLUMN • 3 DISTINCT PARTS • NUCLEUS PULPOSUS • ANNULUS FIBROSUS • CARTILAGINOUS ENDPLATE • MULTIPLE FUNCTIONS • ALLOWS FOR MOVEMENT BETWEEN VERTEBRAL BODIES • SHOCK-...

INTERVERTEBRAL DISC (IVD) ANATOMY FUNCTION BIOMECHANICAL PROPERTIES ANATOMY • IVDS MAKE UP 20-33% OF THE ENTIRE HEIGHT OF THE SPINAL COLUMN • 3 DISTINCT PARTS • NUCLEUS PULPOSUS • ANNULUS FIBROSUS • CARTILAGINOUS ENDPLATE • MULTIPLE FUNCTIONS • ALLOWS FOR MOVEMENT BETWEEN VERTEBRAL BODIES • SHOCK-ABSORBING CONCEPT • TRANSMITS LOADS FROM ONE VERTEBRAL BODY TO THE NEXT • NEUROLOGICAL INPUT – NOCICEPTION AND PROPRIOCEPTION MICROANATOMY • WEIGHT TRANSMISSION AND RESISTANCE TO VARIOUS TYPES OF LOADING DEPENDS UPON • WATER CONTENT OF NUCLEUS AND ANNULUS • FIBER ORIENTATION OF ANNULUS MICROANATOMY • CONSTITUENTS OF IVD • GLYCOSAMINOGLYCANS (GAGS) • PROTEOGLYCAN UNITS AND AGGREGATES • COLLAGEN • ELASTIN • CELLS • WATER! GLYCOSAMINOGLYCANS (GAGS) • LONG CHAINS OF POLYSACCHARIDES FOUND IN MOST FORMS OF CONNECTIVE TISSUE • IVD • CHONDROITIN SULFATE : GREATEST WATER-BINDING CAPACITY • 2X GREATER THAN KERATAN SULPHATE • LOSS OF CHONDROITIN SULPHATE REDUCES THE ABILITY OF THE DISC TO BIND WATER • KERATAN SULFATE: WATER-BINDING CAPACITY • HYALURONIC ACID: ACTS AS A CONNECTING MOLECULE PROTEOGLYCAN AGGREGATES • PROTEOGLYCAN UNITS • MANY GAGS LINKED TO A CORE PROTEIN • CHONDROITIN SULFATE AND KERATAN SULFATE LINK TO CORE PROTEIN • PROTEOGLYCAN AGGREGATES • SEVERAL PROTEOGLYCAN UNITS ARE LINKED TO A HYALURONIC ACID BACKBONE WATER-BINDING CAPACITY OF IVD • PROTEOGLYCAN UNITS AND AGGREGATES ATTRACT AND RETAINING WATER • WATER-BINDING CAPACITY DEPENDS ON THE CONCENTRATION OF CHONDROITIN SULFATE • THIS STRUCTURE AND ABILITY TO RETAIN WATER RESULTS IN THE COMPRESSION RESISTING FUNCTION OF THE IVD COLLAGEN • FUNDAMENTAL UNIT? • TYPE I • WITHSTANDS TENSILE STRESS • HIGHLY CONCENTRATED IN THE ANNULUS • TYPE II • RESISTS PRESSURE • PREDOMINATELY FOUND IN NUCLEUS, BLENDS INTO INNER ANNULUS • COLLAGEN FIBERS BIND PROTEOGLYCANS TO FORM NUCLEUS MATRIX ELASTIN • SMALL AMOUNTS PRESENT IN THE NUCLEUS • 10% OF THE ANNULUS IS MADE OF ELASTIC FIBERS • CONCENTRATED NEAR THE ATTACHMENTS OF THE ANNULUS AND THE ENDPLATE CELLS • FIBROBLASTS AND CHONDROCYTES • 1-5% OF TISSUE VOLUME • MAINTAIN AND REPAIR THE DISC MATRIX • CONCENTRATED NEAR THE END PLATES AND OUTER ANNULUS CLOSER TO BLOOD SUPPLY • SYNTHESIZE COLLAGEN AND PROTEOGLYCAN GEL BIOMECHANICS • IVD SUBJECTED TO CONSIDERABLE FORCES AND MOMENTS • WITHSTANDS LOADS • COMPRESSION STRESS OF BODY WEIGHT • TENSILE, TORSIONAL, BENDING AND SHEER STRESSES DURING PHYSIOLOGICAL MOTION BIOMECHANICS • LOAD CATEGORIES • SHORT DURATION – HIGH AMPLITUDE LOADS • JUMPING, OLYMPIC LIFTS • IRREPARABLE STRUCTURAL DAMAGE WHEN STRESS EXCEEDS ULTIMATE FAILURE STRESS • LONG DURATION – LOW MAGNITUDE LOADS • NORMAL PHYSICAL ACTIVITY • REPETITIVE LOADING LEADS TO FATIGUE FAILURE BIOMECHANICAL BEHAVIOR • BIOMECHANICAL BEHAVIOR IS DEPENDENT UPON: • STRUCTURAL MAKE UP • STATE OF DEGENERATION • AGE DEPENDENT NUCLEUS PULPOSUS • MOSTLY WATER • 70-90% • DECREASES WITH AGE AND TRAUMA • SEMI-FLUID MUCOID MATERIAL WITH CONSISTENCY OF TOOTHPASTE • PROTEOGLYCAN MEDIUM WITH INTERSPERSED FIBRILS OF TYPE II COLLAGEN CREATE THE MATRIX • CHONDROCYTES LOCATED NEAR END PLATES, SYNTHESIZE PROTEOGLYCANS AND COLLAGEN FIBERS • COLLAGEN FIBERS ARE ARRANGED IN LOOSE IRREGULAR MESHWORK NUCLEUS PULPOSUS • BIOMECHANICALLY, THE FLUID NATURE OF THE NUCLEUS ALLOWS FOR DEFORMATION UNDER PRESSURE • THE SHAPE IS ALTERED, BUT THE VOLUME IS UNCHANGED • WHEN THE NUCLEUS IS LOADED IN COMPRESSION, IT TRANSMITS THE APPLIED PRESSURE IN ALL DIRECTIONS ANNULUS FIBROSIS • WATER CONTENT – 60-70% • FORMS THE OUTER BOUNDARY OF THE DISC AND IS GRADUALLY DIFFERENTIATED FROM THE NUCLEUS • COLLAGEN FIBERS ARRANGED IN CONCENTRIC BANDS CALLED LAMELLAE • FIBERS RUN PARALLEL IN EACH BAND, BUT IN OPPOSITE DIRECTIONS BETWEEN TWO ADJACENT BANDS ANNULUS FIBROSIS • THE FIBERS OF THE INNER ANNULUS ARE IMBEDDED IN AND ATTACHED TO THE CARTILAGINOUS END PLATE • THE OUTER (LIGAMENTOUS-TYPE) FIBERS ARE ATTACHED DIRECTLY TO THE BONY VERTEBRAL BODY • SHARPEY’S FIBERS • THE ATTACHMENT OF THE DISC PERIPHERALLY IS STRONGER THAN INTERNALLY ANNULUS FIBROSIS • LAMELLAE ARE THICKER ANTERIORLY AND LATERALLY • POSTERIOR PORTION THINNER • LAMELLAE ARE LOOSELY CONNECTED GIVING THEM CONSIDERABLE DISTENSIBILITY • ANNULUS CAN EXTEND AND BULGE OUTWARD WITH APPLIED LOADS CARTILAGINOUS ENDPLATE • COMPOSED OF BOTH FIBROCARTILAGE AND HYALINE CARTILAGE AND SEPARATES THE NUCLEUS AND ANNULUS FROM THE VERTEBRAL BODY • CONTINUOUS WITH THE INNER ANNULAR FIBERS AND ENCLOSES THE NUCLEUS • APPROXIMATELY 1 MM THICK AND 7080% WATER CARTILAGINOUS ENDPLATE • TISSUE ADJACENT TO BONE CONTAINS MORE COLLAGEN • TISSUE ADJACENT TO NUCLEUS CONTAINS MORE PROTEOGLYCANS AND WATER • POROUS – ALLOWS SMALL MOLECULES TO PASS THROUGH FROM THE VERTEBRAL BODY TO THE CENTER OF THE DISC • IMBIBITION MECHANISM OF WEIGHT TRANSMISSION • NUCLEUS AND ANNULUS BOTH PLAY A ROLE • ANNULUS IN COMPRESSION • DENSELY PACKED LAMELLAE MAKE A RELATIVELY STIFF STRUCTURE AND CREATE BULK • RESISTS BUCKLING AND WITHSTANDS BRIEFLY APPLIED LOADS • ROLLED UP MAGAZINE • DENUCLEATED DISC EXHIBITS THE SAME WEIGHT BEARING CAPACITY AS AN INTACT DISC WITH BRIEF LOADING • SUSTAINED PRESSURE WILL BUCKLE THE COLLAGEN AND WATER WILL BE SQUEEZED OUT OF THE ANNULUS MECHANISM OF WEIGHT TRANSMISSION • NUCLEUS AND ANNULUS BOTH PLAY A ROLE • NUCLEUS IN COMPRESSION • BRACING MECHANISM • HEIGHT DECREASES SLIGHTLY AND NUCLEUS EXPANDS RADIALLY • PUSHES AGAINST ANNULUS • ANNULUS RESISTS RADIAL EXPANSION • EQUILIBRIUM ESTABLISHED • HEALTHY LUMBAR DISC: 88 LB LOAD CAUSES ONLY 1 MM COMPRESSION STRAIN AND .5 MM RADIAL EXPANSION SHOCK ABSORBING PROPERTIES OF IVD • UNDER COMPRESSIVE LOAD COLLAGEN FIBERS OF THE ANNULUS ARE STRETCHED (DEFORMATION) AND ENERGY IS ABSORBED AND STORED • WHEN THE LOAD IS RELEASED, THE ELASTIC RECOIL EXERTS ENERGY BACK ONTO NUCLEUS • DEFORMATION IS REVERSED • RESILIENCY OR SPRINGINESS (THINK MOTION PALPATION – JOINT PLAY) SHOCK ABSORBING PROPERTIES OF IVD • WHEN FORCE IS RAPIDLY APPLIED TO AN IVD IT IS MOMENTARILY DIVERTED INTO STRETCHING THE ANNULUS • THE DIVERSION ATTENUATES THE SPEED OF THE FORCE WHILE THE MAGNITUDE OF THE FORCE REMAINS THE SAME • EVENTUALLY THE FULL FORCE IS TRANSMITTED TO THE NEXT VERTEBRA • SHOCK ABSORPTION PROTECTS THE VERTEBRAL BODY BELOW BY SLOWING DOWN THE TRANSMISSION OF THE APPLIED FORCE CHANGES IN WATER CONTENT OF THE IVD • WATER CONCENTRATION OF THE NUCLEUS IS CRITICALLY IMPORTANT • HYDROSTATIC PRESSURE ALLOWS THE DISC TO RESIST COMPRESSION • ANY CHANGE IN WATER CONTENT OF THE NUCLEUS WILL ALTER MECHANICAL PROPERTIES OF THE IVD CHANGES IN WATER CONTENT OF THE IVD • IF THE DISC CAN’T ATTRACT AND RETAIN WATER THE DISC CAN’T BUILD SUFFICIENT FLUID PRESSURE • LOAD-TRANSFERRING MECHANISM IS ALTERED • END PLATES ARE SUBJECTED TO LESS PRESSURE AT THE CENTER • LOADS ARE DISTRIBUTED TO THE PERIPHERY OF THE ANNULUS WHICH MAY RESULT IN BUCKLING OF THE ANNULUS • RESULTS IN DAMAGE TO ANNULUS ANNULAR FISSURES AKA TEARS • RESULT FROM ALTERED BIOMECHANICAL PROPERTIES (CAUSED BY WATER LOSS) AND REPETITIVE MOVEMENTS OVER TIME • TYPES • CONCENTRIC FISSURES • BETWEEN LAMELLAE • RADIAL FISSURES • ACROSS LAMELLAE • WEAKEN THE ANNULUS AND CAN ULTIMATELY LEAD TO NUCLEUS HERNIATION THROUGH ANNULUS FIBROSUS MOVEMEN TS OF THE INTERBOD Y JOINT (IBJ) • WHEN UNRESTRICTED BY THE POSTERIOR ELEMENTS TWO VERTEBRAL BODIES UNITED BY THE IVD CAN MOVE IN ANY DIRECTION • IVD ACTS AS A SPACER KEEPING VERTEBRAL BODIES SEPARATED • IVD IS CAPABLE OF DEFORMATION IN ALL PLANES OF MOTION MOVEMENTS OF IBJ TENSION • DISTRACTION OF THE IBJ • RESULTS IN SEPARATION OF THE VERTEBRAL BODIES AND INCREASED HEIGHT OF IVD • ALL COLLAGEN FIBERS UNDERGO TENSION STRESSES AND TENSILE STRAIN REGARDLESS OF THEIR ORIENTATION • NOT A COMMON ACTIVITY OF DAILY LIVING MOVEMENTS OF IBJ SHEAR • SHEAR STRESSES CAUSES TRANSLATION OF ONE VERTEBRAL BODY UPON THE OTHER • SLIDING MOVEMENTS PRODUCED BY SHEAR FORCES CAUSE COLLAGEN FIBERS TO BEHAVE DIFFERENTLY DEPENDING ON THEIR LOCATION WITHIN THE ANNULUS • FIBERS ORIENTED IN THE DIRECTION OF MOVEMENT UNDERGO TENSION • FIBERS IN EVERY SECOND LAMELLA WILL BE RELAXED • DISC IS SUBJECTED TO SHEAR STRESSES DURING BENDING AND TORSIONAL LOADING • DISC RESISTS HORIZONTAL SHEAR FORCES, INJURY DUE TO PURE SHEAR LOADING IS RARE MOVEMENTS OF IBJ BENDING • BENDING OR ROCKING LOWERS ONE END AND RAISES THE OPPOSITE END • DISTORTION OF ANNULUS AND NUCLEUS • COMPRESSION OF ANNULUS IN THE DIRECTION OF MOVEMENT • TENSION OF ANNULUS ON THE SIDE OPPOSITE OF MOVEMENT MOVEMENTS OF IBJ TORSION • AXIAL ROTATION • FIBERS ORIENTED IN DIRECTION OF TWISTING UNDERGO TENSION • FIBERS IN EVERY SECOND LAYER ARE RELAXED • TWISTING MOVEMENTS ARE ASSOCIATED WITH ANNULUS INJURY COMPRESSIVE LOADS ON IVD • DISC AND FACET JOINTS CARRY COMPRESSIVE LOADS THAT THE TRUNK IS SUBJECTED TO • IN ERECT STANDING POSTURE, FORCES ON THE DISC ARE GREATER THAN THE WEIGHT OF THE TRUNK DUE TO SPINAL CURVES AND MUSCLE CONTRACTION • IN SITTING POSITION, FORCES ON THE DISC ARE MORE THAN 3X THE WEIGHT OF THE TRUNK • DURING FORWARD BENDING, TRUNK MUSCLES CONTRACT TO CONTROL BENDING RESULTING IN AN OVERALL INCREASE OF COMPRESSIVE FORCES • DYNAMIC MOVEMENTS CREATE THE HIGHEST COMPRESSION LOADS COMPRESSION TESTS • LOAD DEFORMATION CURVE IS SIGMOIDSHAPED • LITTLE RESISTANCE AT LOW LOADS • MORE FLEXIBLE • HIGHER RESISTANCE WITH INCREASED LOADS • MORE STABLE COMPRESSION TESTS • HIGH COMPRESSIVE LOADS • HERNIATIONS THROUGH ANNULUS FIBROSIS DUE TO COMPRESSIVE LOADS IS RARE! • FAILURE OF VERTEBRAL BODY AND END PLATE IS MUCH MORE COMMON • COMPRESSION FRACTURE OF VERTEBRAL BODY OR END PLATE FRACTURE • MIGRATION OF NUCLEUS INTO THE VERTEBRAL BODY (SCHMORL’S NODE) COMPRESSION TESTS • WITH CENTRAL COMPRESSIVE LOADING, THE DISC BULGES IN HORIZONTAL PLANE EQUALLY IN ALL DIRECTIONS • TENDENCY FOR THE DISC TO HERNIATE THROUGH POSTERO-LATERAL PORTION OF ANNULUS IS RESULT OF REPETATIVE LOADING SITUATION • FLEXION AND LATERAL BENDING TENSILE LOADS • TENSILE STRESSES ARE PRODUCED IN PARTS OF THE ANNULUS DURING NORMAL PHYSIOLOGIC MOTIONS • FLEXION • EXTENSION • LATERAL FLEXION • AXIAL ROTATION • COMPRESSION