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Bone structure and clinical importance
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BONE STRUCTURE AND ITS CLINICAL IMPORTANCE
Dr GIRIDHAR BOYAPATI P.G
What is Bone? – Mineralized connective tissue
- constitute part of the endoskeleton of vertebrates
Classification
REGION- Axial, Appendicular
SHAPE - Long bones, short bones, irregular, pneumatic, sesamoid, accessory
STRUCTURE Macroscopic – Compact
Spongy
Microscopic – Lamellar (Secondary Bone) Woven/fibrous(Primary Bone)
DEVELOPMENT – Membranous Cartilaginous
Membrano-cartilaginous
ENDOCHONDRAL OSSIFICATION
MESENCHYMAL CELLS
CHONDROBLASTS
CHONDROCYTES
CARTILAGE MODEL OF FUTURE BONE
OSTEOBLASTS
Endochondral Ossification
Endochondral Ossification
Endochondral Ossification Defects – AD Inheritance
• Achondroplasia
• Thanatophoric Dysplasia
• Hypochondroplasia
Mutation in FGFR 3 gene
Intramembranous Ossification
EXAMPLES OF INTRAMEMBRANOUS OSSIFICATION
1. EMBRYONIC FLAT BONES : SKULL, PELVIS, MAXILLA, MANDIBLE, CLAVICLE
2. DISTRACTION OSTEOGENESIS
3. FRACTURE HEALING WITH RIGID FIXATION
4.BLASTEM BONE
PERIOSTEAL OSSIFICATION
OSTEOGENIC CELLS FROM PERIOSTEUM
LAY PARLLEL LAYERS OF COMPACT BONE
Bone cells
Osteo progenitors(Pleuripotent stem cells)
Osteoblasts ("bone makers")
Osteocytes ("bone cells")
Osteoclasts (“bone breakers”) remodeling
MATRIXGround substance
ProteoglycansGlycoproteinsMineralsWater
Fibers
Cells of Bone (Primary/Temporary)
Osteoprogenitor
Osteoclast
Osteoblast
Osteocyte
Osteoid
PERIOSTEUM
MEMBRANE COVERING OUTER SURFACE OF BONE
LAYERS: 1. FIBROUS LAYER 2. CAMBIUM LAYER
OSTEOGENIC CELLS
OSTEOBLAST
OSTEOCYTE
OSTEOCLAST
Osteoclast
CANALICULI
Bone cells -Function• Osteoblasts – Matrix synthesis – Osteoid,
Calcification
PTH receptors
• Osteocyte – Maintanace of Matrix by intercellular sickling systems
• Osteoclast – Digestion of collagen, dissolving hydroxyapatite
* Calcitonin receptors
Bone cells- Medical applicationRate of bone apposition – Bone growth
Osteomalacia – Impaired mineralization
Osteitis fibrosa cystica – osteoclast activityOsteopetrosis – “Marble bones” – Bone resorption
defect due to osteoclastic activityOsteitis deformans (Paget’s disease) –Uncontrolled
osteoclast activity followed by osteoblastic activity (incomplete)- Stops at osteoid level
BIOCHEMISTRY
1.INORGANIC 65 -70%2.ORGANIC 30-35%
ORGANIC: a. collagen 90-95% b. pps 4-5% c.Lipids 0.1% INORGANIC 90% Calcium and phosphate
BONE COLLAGEN
1.AXIAL PERIODICITY OF 640 TO 700A
2.PROTIEN COMPOSITION WITH ONE THIRD GLYCINE
3.LARGE NO. OF ALANINE RESIDUES
4.CYSTEINE IS COMPLETELY ABSENT
Matrix
• Fibers – Collagen Type I- Gene mutation in alfa 1or 2 OSTEOGENESIS IMPERFACTA
• Ground substance
Proteoglycans – Chondroitin Sulphate, Keratan Sulphate
Glycoproteins – Osteocalcin , Alkaline phosphatase
Structural regions of long bone
Gross structure of typical long bone Shaft – Thick compact bone+ medullary cavity Ends- Cancellous bone + thin compact layer Articular cartilage – No periosteum, avascular Periosteum – Fibrous + cellular
Shape, nutrition, attachment
fracture repair, sensitive Endosteum – Cellular -Repair
and remodelling Nutrient foramen – mid shaft Bone marrow – Red, Yellow
Parts of a growing bone
Epiphysis
(Secondary) Epiphyseal
plate Metaphysis Diaphysis
(Primary)
TYPES OF EPIPHYSIS
PRESSURE
region of the long bone that forms the joint is called Pressure Epiphysis
ARTICULAR....WT TRANSMISSON
EX: HEAD OF FEMUR AND HUMERUS
TRACTIONNon-articularMuscle pullOssifies later than Pressure
.EX HUMERUS G.T AND L.T FEMUR G.T AND LT
ATAVISTICCOROCOID PROCESS OF SCAPULAOS TRIGONUM
ABERRANTHEAD OF 1ST METACARPEL
Unusual
Epiphyseal plate
Growth Plate
ZONE 1INJURY CAUSES CESSATION OF GROWTH
ZONE 2BONE LENGTH IS ADDED
ZONE 3WEAKEST PORTION OF GROWTH PLATE
Metaphysis
Epiphyseal end of diaphysis
Active growth Before fusion
end arteries, hair pin bends
OSTEOMYELITIS
Blood supply of bones
Long Bone Nutrient artery Metaphyseal arteries Epiphyseal arteries Periosteal arteries
Short Bone - Nutrient artery; Periosteal arteries
Vertebra- Body, Processes
Rib - Nutrient artery; Periosteal arteries
Nutrient artery Mid shaft Tortuiosity 2/3rd inner compact bone Hair pin loops Direction – away from
growing end
.
“To the elbow I go. From the knee I flee.”
Nutrient Artery
1.Enters into the diaphysis of long bones through an oblique canal
2.direction of canal is determined by relative amount of growth that has occurred at proximal and distal ends of the bone;
3.does not branch within the cortex, divides after reaching the medullary cavity,
4. direction of blood flow is centrifugal;
Disruption of Nutrient Artery causes
1. In growing bone can result in necrosis of large portion of marrow & of inner two thirds of cortex
2. This cortical death does not occur in adult bone because combined epiphyseal-metaphyseal collateral circulation is developed enough to maintain these areas;
3.loss of circulation in terminal vessels of nutrient artery of growing bone will interfere with enchondral ossification;
Epiphyseal arteries
In femoral and radial heads, which are almost entirely covered by cartilage vessels enter in region between articular cartilage & growth-plate cartilage
In other regions, the epiphysis has openings that permit passage of large number of vessels into and out of the ossification centers
Obliteration of epiphyseal blood supplycauses
1.necrosis of epiphysis
2. longitudinal growth ceases
3. permanent closure of epiphyseal plate
METAPHYSIAL ARTERIES
BRANCHES OF SYSTEMIC VESSELS
Epiphyseal vessels are responsible for permitting longitudinal growth to occur, whereas metaphyseal vessels nourish
osteoprogenitor cells, which lay down bone on cartilage matrix;
PERIOSTEAL ARTERIES
Periosteal vessels send small branches thru minute channels in cortex to supply about outer 1/3 of cortex
Extensive network of vessels covers entire length of the bone shaft
Anastomoses with adjacent skeletal muscles so in cases in which the nutrient artery of muscle has been damaged, then periosteal vessels may temporarily serve as the primary blood supply;
BLOOD SUPPLY OF GROWTH PLATE
growth plate itself is avascular & receives nutrition from 2 sources
1.epiphyseal vessels that supply germinal, proliferating, and upper hypertrophic cell layers by diffusion
2 .metaphyseal vessels that supply zone of provisional calcification
In a young child, epiphyseal vessels are separated from metaphyseal vessels, but
following growth arrest of the cartilage plate, there is
an extensive anastomoses between epiphyseal vessels, metaphyseal vessels, &
terminal branches of Nutrient Artery;
VENOUS DRAINAGE
TRANSVERSE VENOUS CHANNELS
CENTRAL VENOUS SINUS
NUTRIENT VEIN
-ONLY 5-10% OF VENOUS DRINAGE IS THROUGH NUTRIENT VEIN
-REMAINING IS THROUGH PERIOSTEAL VENOUS DRINAGE
Circulatory disturbances
PHYSIS AND EPIPHYSIS1.Legg–Calve–Perthes Disease: Circulatory disturbance to the capital
femoral epiphysis 2.Physeal TraumaMETAPHYSIS1.Haematogenous Osteomyelitis2.Metastasis.DIAPHYSIS1.Intramedullary Reaming2.Fracture HealingPERIOSTEAL BLOOD SUPPLY1.Paralytic conditions
Spongy bone
1. loose network of bone trabecule
2. interconnected
3. arranged along lines of maximum stress
Spongy Bone
Superimposed lamllaeNo Haversian systemLamellated trabeculae Red marrow
Spongy Bone- No HS
Osteon (Haversian system) Central canal (Haversian
or osteonal canal) Transverse (Volkmann)
canals Lacuna Canaliculi ("tiny canals") Lamellae
Concentric,Intersititial,
Circumferential
Compact bone
COMPACT BONE
Sharpey’s fibers
Connective tissue matrix
Bundles of collagen fibers Connect Perisoteum to Bone
Fibrous layer of Periosteum to outer circumferential and interstitial lamellae
Growing Bone
BONE GROWTH1. Appositional
2. Endochondral
Factors affecting growth of a bone
Nutritional Vit. A - Co-ordination of osteoblastic and
osteoclastic activity
Vit.C – Synthesis of organic matrix
Vit.D – Absorption of Ca, P
Rickets, Osteomalacia (Calcification deficiency)
Calcium – Decalcification of bone
Factors affecting growth of a bone
Hormonal – • Pituitary - GH- Dwarfism; Gigantism,
Acromegaly• Thyroid - Calcitonin
Parathyroid – PTH Decalcification
Sex Hormones - Androgens, estrogens - Stimulators Mechanical factors
Tensile forces – Bone formation
Compressive forces – Bone resorption
Ossification Centre
Rules of Ossification Primary centers - before birth
except carpal and tarsal (except calcaneus, talus, cuboid)
Secondary centers - after birth
except lower end of femur, upper end of tibia, humerus
Center which appears first unites last
except lower end of FIBULA
Rules of Ossification Center which appears later unites first
except upper end of fibula Direction of nutrient artery - away from
growing end
except fibula Growing end is one where center
appears first and unites last
except fibula
Fracture Healing1. Hematoma
formation Macrophages
Osteoclasts2. Fibrocartilaginous
callus formation Periosteum Endosteum 3. Bony callus
formation Ossification (EC & IM)4. Remodeling Sec.bone formation
Bone remodeling cycle