ANATOMY OF BONE AND CARTILAGE

ANATOMY OF BONE AND CARTILAGE Presenter - Dr. Vinay Jain K

CONTENTSFORMATION OF BONECLASSIFICATION OF BONESSTRUCTURE OF BONEBLOOD SUPPLYCOMPOSITION OF BONEFRACTURE HEALINGCARTILAGETYPES OF CARTILAGE

BONE (syn Os; Osteon)Osseous tissue, a specialised form of dense connective tissue consisting of bone cells (osteocytes)Embedded in a matrix of calcified intercelluar substanceBone matrix contains collagen fibres and the minerals calcium phosphate and calcium carbonate

FORMATION OF BONEThe process of bone formation - ossificatiomAll bone is of mesodermal originTwo types of ossificationIntramembranous ossificationEndochondral ossification

INTRAMEMBRANOUS OSSIFICATIONMesenchymal condensationHighly vascularLaying down of bundles of collagen fibres in the mesenchymal condensationOsteoblast formation OSTEOIDCalcium salts deposition lamellus of bone

BONE FORMATION- Intramembranous ossification

6

BONE FORMATION - Intramembranous ossification

7

BONE FORMATION - Intramembranous ossification

8

BONE FORMATION - Intramembranous ossification

9

ENCHONDRAL OSSIFICATIONOssifies bones that originate as hyaline cartilgeMost bones originate as hyaline cartilageGrowth and ossification of long bones occurs in 6 steps

STEP 1Chondrocytes in the center of hyaline cartilage:

enlarge

form struts and calcify

die, leaving cavities in cartilage

STEP 2Blood vessels grow around the edges of the cartilage

Cells in the perichondrium change to osteoblasts:

producing a layer of superficial bone around the shaft which will continue to grow and become compact bone (appositional growth)

STEP 3 Blood vessels enter the cartilage:

bringing fibroblasts that become osteoblasts

spongy bone develops at the primary ossification center

STEP 4Remodeling creates a marrow cavity:

bone replaces cartilage at the metaphyses

STEP 5Capillaries and osteoblasts enter the epiphyses:

creating secondary ossification centers

STEP 6Epiphyses fill with spongy bone:

cartilage within the joint cavity is articulation cartilage

cartilage at the metaphysis is epiphyseal cartilage

Endochondral ossificationStages 1-3 during fetal week 9 through 9th month Stage 4 is just before birthStage 5 is process of long bone growth during childhood & adolescence

SKELETAL ORGANIZATION The actual number of bones in the human skeleton varies from person to person

Typically there are about 206 bones

For convenience the skeleton is divided into the: Axial skeleton Appendicular skeleton

DIVISION OF SKELETON Axial Skeleton Skull Spine Rib cageAppendicular Skeleton Upper limbs Lower limbs Shoulder girdle Pelvic girdle

CLASSIFICATION OF BONES BY SHAPELong bonesShort bonesFlat bones Irregular bonesPneumatized bonesSesamoid bones

(Short bones include sesmoid bones)

LONG BONESDiaphysis shaftEpiphysis expanded endsShaft 3 surfaces, 3 borders, medullary cavity and a nutrient foramen directed away from the growing endEx humerus, radius, ulna, femur, etc

SHORT BONESAre small and thickTheir shape is usually cuboid, cuneifrom, trapezoid or scaphoidEx carpal and tarsal bones

FLAT BONESAre thin with parallel surfaces

Are found in the skull, sternum, ribs,and scapula Form boundaries of certain body cavities

Resembles a sandwich of spongy bone

Between 2 layers of compact bone

PNEUMATIC BONES (Gr. pert. to air)Certain irregular bones contain large air spaces lined by epitheliumMake the skull light in weight, help in resonance of voice, and act as air conditioning chambers for inspired airEx maxilla, sphenoid, ethmoid, etc

SESAMOID BONESResembling a grain of sesame in size or shapeBony nodules found embedded in the tendons or joint capsulesNo periosteum and ossify after birthRelated to an articular or nonarticular bony surfaceEx patella, pisiform, fabella, etcFunctions

IRREGULAR BONESHave complex shapes Examples: spinal vertebrae pelvic bones

DEVELOPEMENTAL CLASSIFICATIONMembrane (dermal) bonesCartilaginous bonesMembrano-cartilagenous bones

Membrane (dermal) bonesOssify in membrane (intramembranous of mesenchymal)Derived from mesenchymal condensationsEx bones of the vault of skull and facial bonesDefect cleidocranial dysostosis

Cartilaginous bonesOssify in cartilage (intracartilagenous or endochondral)Derived from preformed cartilaginous modelsEx bones of limbs, vertebral column and thoracic cageDefect common type of dwarfism called achondroplasia

Membrano-cartilaginous bonesOssify partly in cartilage and partly in membraneEx clavicle, mandible, occipital, etc

STRUCTURE OF BONE

BONE CELLSELEMENTS COMPRISING BONE TISSUEIt consists of bone cells or osteocytes separated by intercellular substanceOsteoblasts bone producing cellsOsteoclasts bone removing cellsOsteoproginator cells from which osteoblasts and osteoclasts derived

CELLS OF BONE TISSUE

OSTEOPROGENITOR CELLSMesenchymal stem cells that divide to produce osteoblasts

Are located in inner, cellular layer of periosteum (endosteum)

Assist in fracture repair

OSTEOBLASTS (Gr.- osteon-bone, blastos germ)Immature bone cells that secrete matrix compounds (osteogenesis)Osteoid Matrix produced by osteoblasts, but not yet calcified to form bone

Osteoblasts surrounded by bone become osteocytes

OSTEOCYTEMature bone cells that maintain the bone matrix

Live in lacunae

Are between layers (lamellae) of matrix

Connect by cytoplasmic extensions through canaliculi in lamellae

Do not divide

OSTEOCLAST (Gr.- osteonbone, +klan-to break) Secrete acids and protein digesting enzymes

Giant, mutlinucleate cells Dissolve bone matrix and release stored minerals (osteolysis)

Are derived from stem cells that produce macrophages

STRUCTURAL CLASSIFICATIONMacroscopicallyCompact boneCancellous bone

COMPACT BONEStrong dense 80% of the skeletonConsists of multiple osteons (haversian systems) with intervening interstitial lamellaeBest developed in the cortex of long bonesOsteons are made up of concentric bone lamellae with a central canal (haversian canal) containing osteoblasts and an arteriole supplying the osteon

Contd.Lamellae are connected by canaliculi Cement lines mark outer limit of osteon (bone resorption ended)Volkmanns canals: radially oriented, have arteriole, and connect adjacent osteonsThis is an adaptation to bending and twisting forces (compression, tension and shear)

OSTEONThe basic unit of mature compact bone Osteocytes are arranged in concentric lamellae

Around a central canal containing blood vessels

CANCELLOUS BONE (SPONGY OR TRABECULAR)Open in texture meshwork of trabeculae (rods and plates)Crossed lattice structure, makes up 20% of the skeletonHigh bone turnover rateBone is resorbed by osteoclasts in Howships lacunae and formed on the opposite side of the trabeculae by osteoblastsOsteoporosis is common in cancellous bone, making it susceptible to fracturesCommonly found in the metaphysis and epiphysis of long bonesAdaptation to compressive forces

Contd.Does not have osteons

The matrix forms an open network of trabeculae

Trabeculae have no blood vessels

Cancellous Bone

MicroscopicallyLamellar bone Woven bone

LAMELLAR BONEBone is made up of layers or lamellaeLamellae is a thin plate of bone consisting of collagen fibres and mineral salts, deposited in gelatinous ground substanceBetween adjoining lamellae we see small flattened spaces lacunae

LAMELLAR BONE

Contd.Lacunae Contains one osteocyteHave fine canals or canaliculi that communicate with those from other lacunae

Fibers of one lamellus run parallel to each other, but those of adjoining lamellae run at varying angles to each other.

WOVEN BONEFound in all newly formed bone later replaced by lamellar boneCollagen fibres are present in bundles - run randomly interlacing with each otherAbnormal persistence pagets disease

PrimaryImmatureWovenSecondaryMatureLamellar

MICROSCOPIC MACROSCOPIC

56

GROSS STRUCTURE OF AN ADULT LONG BONEShaft Two ends

SHAFTComposed of periosteum,cortex and medullary cavity

PERIOSTEUMExternal surface of any bone covered by a membrane periosteumTwo layerOuter fibrous membrane, inner cellularIn young bones inner layer numerous osteoblasts osteogenitic layerIn adults osteoblasts are not conspicuous, but osteoprogeniter cells present here can form osteoblasts when need arises

PERIOSTEUM

PERIOSTEUM

FUNCTIONSMedium through which mucles, tendons and ligaments are attachedForms a nutritive functionCan form bone when requiredForms a limiting membrane that prevents bone tissue from spilling out into neighbouring tissues

CORTEX

Is made up of a compact bone which gives the desired strengthCan withstand all possible mechanical strains

ENDOSTEUM An incomplete cellular layer: lines the marrow cavity covers trabeculae of spongy bone lines central canals

Contains osteoblasts, osteoprogenitor cells, and osteoclasts

Is active in bone growth and repair

MEDULLARY CAVITY Filled with red or yellow bone marrowRed at birth haemopoiesisYellow as age advance atrophies fattyRed marrow persists in the cancellous ends of long bones

PARTS OF YOUNG BONE

It ossifies in 3 partsThe two ends from the secondary centersIntervening shaft from a primary center

EPIPHYSIS (Gr., a growing upon)The ends of a bone which ossify from secondary centersTypes Pressure epiphysis transmission of the weight . Ex- head of femur, etcTraction epiphysis provides attachment to one or more tendons which exerts a traction on the epiphysis. Ex- trochanters of femur,et

Atavistic epiphysis phylogenitically an independent bone , which fuses to another bone. Ex- coracoid process of scapula,etcAberrant epiphysis not always present. Ex- head of the 1st metacarpal and base of other metcarpal

DIAPHYSIS(Gr., a growing through)It is the elongated shaft of a long bone which ossifies from a primary centerMade of thick cortical boneFilled with bone marrow

METAPHYSIS(Gr. meta, after, beyond, + phyein, to grow)Epiphysial ends of a diaphysisZone of active growthTypically made of cancellous boneHair pin bends of end arteries

EPIPHYSIAL PLATE OF CARTILAGEIt separates epiphysis from the metaphysis.Proliferation responsible for lengthwise growth of the long boneEpiphysial fusion can no longer growNourished by both epiphysial and metaphysial arteries

BLOOD SUPPLY OF BONESLONG BONES derived fromNutrient arteryPeriosteal arteryEpiphysial arteryMetaphysial artery

Nutrient artery

Enters through the nutrient foramenDivides into ascending and descending branches in the medullary cavityBranch divides small parallel channels terminate in adult metaphysis

Anastomosing with the epiphysial, metaphysial and periosteal arteriesSupplies the medullary cavity , inner 2/3 of the cortex and metaphysisNutrient foramen is directed away from the growing end of the bone

Periosteal arteries

Numerous beneath the muscular and ligamentous attachments

Ramify beneath the periosteum and enter the volkmanns canals to supply the outer 1/3 of the cortex

Epiphysial arteriesDerieved from periarticular vascular arcades (circulus vasculosus)Out of the numerus vascular foramina in this region few admit arteries and rest venous exitsNumber size idea of the relative vascularity of the two ends of long bone

Metaphysial arteriesDerived from the neighbouring systemic vesselsPass directly into the metphysis and reinforce the metaphysial branches from the primary nutrient artery

HOMEOSTASIS OF BONE TISSUE Bone Resorption action of osteoclasts and parathyroid hormone aka parathormone aka PTH

Bone Deposition action of osteoblasts and calcitonin

Occurs by direction of the thyroid and parathyroid glands

MCOC

FACTORS AFFECTING BONE TISSUEDeficiency of Vitamin A retards bone development Deficiency of Vitamin C results in fragile bones Deficiency of Vitamin D rickets, osteomalacia Insufficient Growth Hormone dwarfism Excessive Growth Hormone gigantism, acromegaly Insufficient Thyroid Hormone delays bone growth Sex Hormones promote bone formation; stimulate ossification of epiphyseal plates Physical Stress stimulates bone growth

CHEMICAL ANALYSIS OF BONE

APPLIED ANATOMYPeriosteum is particularly sensitive to tearing or tension Drilling into the compact bone without anaesthesia causes only dull pain Drilling into spongy bone is much more painfulFractures, tumours and infections of the bone are very painful

Blood supply of bone is so rich that it is very difficult to sufficiently to kill the bone

Contd.In rickets calcification of cartilage fails and ossification of the growth zone is disturbed Osteoid tissue is formed normally and the cartilage cells proliferate freely ,Mineralization does not takes place

Scurvy formation of collagenous fibres and matrix is impairedOsteoporosis - Bone resorption proceeds faster than deposition

FRACTURE HEALINGSTAGES OF FRACTURE HEALINGStage of inflammationStage of soft callous formationStage of hard callous formationStage of remodelling

STAGE OF INFLAMMATION

STAGE OF SOFT CALLUS FORMATION

STAGE OF HARD CALLUS FORMATION

STAGE OF REMODELLING

MECHANISM OF BONE HEALING

Direct (primary) bone healingIndirect (secondary) bone healing

DIRECT BONE HEALINGMechanism of bone healing seen when there is no motion at the fracture site (i.e. absolute stability)Does not involve formation of fracture callusOsteoblasts originate from endothelial and perivascular cells

A cutting cone is formed that crosses the fracture site Osteoblasts lay down lamellar bone behind the osteoclasts forming a secondary osteonGradually the fracture is healed by the formation of numerous secondary osteonsA slow process months to years

INDIRECT BONE HEALINGMechanism for healing in fractures that have some motion, but not enough to disrupt the healing process

Bridging periosteal (soft) callus and medullary (hard) callus re-establish structural continuity

Callus subsequently undergoes endochondral ossification

Process fairly rapid - weeks

BONE REMODELLINGWOLFFs LAW remodeling occurs in response to mechanical stress

Increasing mechanical stress increases bone gainRemoving external mechanical stress increases bone loss which is reversible on (to varying degrees) on remobilzation

Contd.PIEZOELECTERIC REMODELING occurs in response to electric chargeThe compression side of bone is electronegative stimulating osteoblastsTension side of the bone is electropositive, stimulating osteoclasts

CARTILAGE

CARTILAGE (L.-cartilago gristle)It is a connective tissue composed of cells (chondrocytes) and fibres (collagen) in matrix, rich in mucopolysaccaridesGroung substance chemically GAGCore protein aggrecanCollagen type 2Fibrocartilage and perichondrium type 1

General featuresHas no blood vessels or lymphaticsNutrition is by diffusion through matrixNo nerves insensitiveSurrounded by a fibrous membrane perichondriumArticular cartilage has no perichondrium regeneration after injury inadequateWhen calcifies chondrocytes die replaced by bone

TYPESHYALINE CARTILAGEFIBROCARTILAGEELASTIC CARTILAGE

HYALINE CARTILAGE(G. hyalos - transparent stone)Bluish white and transparent due to very fine collagen fibresAbundantly distributed tendency to calcify after 40yrs of ageAll cartilage bones are preformed in hyaline cartilageEx articular cartilage, costal cartilage

FIBROCARTILAGEWhite and opaque due to abundance of dense collagen fibresWhenever fibres tissue is subjected to great pressure replaced by fibrocartilageTough, strong and resilientEx intervertebral disc, intraarticular disc

Fibrocartilage

ELASTIC CARTILAGEMade of numerous cells and Rich network of yellow elastic fibres pervading the matrix so that it is more pliableCartilage in the external ear, auditory tube

Elastic cartilage

THANK YOU