anatomy of bone
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Anatomy of bone
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The skeletal system is
divided into two
functional parts:-
Axial skeleton ---
head , neck & trunk
Appendicular---limbs( including
pectoral and pelvic
girdles)
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The skeleton is made of cartilage and bones. The
five major functions of the skeleton are:-
Support
Protection
Movement
Storage
Blood cell production
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Cartilage is a resilient, semirigid form of
connective tissue that forms parts of the
skeleton where more flexibility is recquired.
Bone is a living tissue which is a hard form ofhighly specialized connective tissue that
makes up most of the skeleton.
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Cartilage
Is an avascular form of connective tissue that
consists of extracellular matrix embedded in a
matrix that contains cells localized in small
cavities. The amount and kind of extracellular
fibers in the matrix varies depending on the
type of cartilage.
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The functions ofcartilage are:-
Support soft
tissues Provide a
smooth,gliding surface
for bonearticulationsat joints
Enable the
developmentand growth oflong bones
Macroscopical joint lesions in sows. a: Cartilage erosion (arrows)
on the medial humeral condyle. b: Cartilage ulceration (arrow)
on the medial femoral condyle. c: Cartilage repair (arrow) of the
medial femoral condyle d: Marginal osteophytes (arrows) on
processus anconeus of ulna.
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There are 3 types of cartilage:-
Hyaline-most common. Its matrix contains amoderate amount of collagen fibers( e,g.articular surfaces of bones)
Elastic-matrix contains collagen fibers along
with a large number of elastic fibers ( e.gexternal ear)
Fibrocartilage-matrix contains a limited
number of cells and ground substance amidsta substantial amount of collagen( e.g.intervertebral disc)
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BoneConsists of an intercellular calcified matrix,
which also contains collagen fibers, andseveral types of cells within the matrix.
Bone Maturity
woven ( immature bone)
Here collagen fibres are aligned randomly and
have no lamellae,making the bone weaker and
more flexible than lamellar bone.
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Lamellar ( mature) bone
Forms the structural component of cortical
and cancellous bone with stress-oriented
collagen fibres contributing to its anisotropic
characteristics.
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Histological cut showing details of lamellar bone concentricallyorganized and woven bone mixed with cartilage and calcifiedcartilage tissues (HE).
Matos et al.Journal of Orthopaedic Surgery and Research 2008
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Two types of bones;compact and spongy
bone( trabecular orcancellous). Compactbone is dense that formsthe outer shell of all
bones and surroundsspongy bone. Spongybone consists of spicules
of bone enclosing cavitiescontaining blood-formingcells( marrow).
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Cortical
(compact
bone)
Comprises of 80 % of adult skeleton forming thenevelope of cuboid bones and the diaphysis of
long bones. Contains lamellae that are laid down
as concentric rings forming trabecular lamellae
systems called osteons or haversian systems.
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Cancellous ( trabecular bone)
Found mainly in the metaphyses and epiphyses of long bones and centrallyin cuboid bones. Its has a 3D lattice of interconnecting trabeculae which arealigned along axes of mechanical stress, enclosing elements of bone marrow.Each of the trabeculae is made up of parallel sheets of lamellae.
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Classification of bones is by shape
Long bones are tubular e.g humerus, femur
Short bones are cuboidal e.g bones of wrist
and ankle
Flat bones consist of two compact bones
plated separated by spongy bone e.g skull
Irregular bones are bones with various shapes
e.g bones of the face
Sesamoid bones are round or oval bones that
develop in tendons
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Bone structure
All bones are derived from mesenchyme (embryonicconnective tissue) by two different processes:
Intramembranous ossification( directly frommesenchyme)-mesenchymal models of bones formduring the embryonic period and direct ossification ofthe mesenchyme begins in the fetal period.
Endochondral ossification( from cartilage derived frommesenchyme) cartilage models of the bones formfrom mesenchyme during the fetal period and bonesubsequently replaces most of the cartilage.
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Mesenchymal cells differentiate into
chondroblasts-forming a cartilaginous bonemodel- midregion of cartilage calcifies-
periosteal capillaries( from fibrous sheath
surrounding the model)- grow into thecalcified cartilage of the bone model and
supply its interior.
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Most secondary ossificationcentres appear in otherparts of the developing
bone after birth; the partsof a bone ossified fromthese centres are epiphyses.
Epiphyseal arteries grow intodeveloping cavities withassociated osteogenic cells.The flared part of thediaphysis nearest theepiphyses is the metaphysis.
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Gross Structures of Bone
The gross structure of a long bone can be
divided into several regions.
Epiphysis
In the long bones, the epiphysis is the regionbetween the growth plate or growth plate scarand the expanded end of bone, covered by
articular cartilage. An epiphysis in a skeletallymature person consists of abundanttrabecular bone and a thin shell of corticalbone.
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Cortical bone is
composed of
haversiansystems
(osteons). Each
osteon has acentral haversian
canal and
peripheral
concentric layers
of lamellae.
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Metaphysis
The metaphysis is thejunctional region
between the growthplate (see the imagebelow) and thediaphysis. Themetaphysis containsabundant trabecularbone, but the corticalbone thins hererelative to thediaphysis. This regionis a common site formany primary bonetumors and similarlesions.
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Growth
plate
The relative predilection of osteosarcoma for the metaphyseal region of long
bones in children has been attributed to the rapid bone turnover due to extensive
bone remodeling during growth spurts.
Di h i
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Diaphysis
The diaphysis is the shaft of long bones and is
located in the region between metaphyses,
composed mainly of compact cortical bone. Themedullary canal contains marrow and a small
amount of trabecular bone.
Physis (epiphyseal plate, growth plate)
The physis is the region that separates the
epiphysis from the metaphysis. It is the zone ofendochondral ossification in an actively growing
bone or the epiphyseal scar in a fully grown bone.
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Blood Supply
Bones are richly supplied with
blood vessels. Most apparent arenutrient arteries that ariseindependent branches of adjacentarteries outside the periosteumand pass obliquely through thecompact bone of the shaft of a
long bone via nutrient foramina.
The nutrient artery divides inthe medullary cavity intolongitudinal branches thatproceed toward each endsupplying the bone marrow,spongy bone and deeper portionsof compact bone.
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The ends of bones are supplied by metaphysial and epiphysial arteries that
arise mainly from the arteries that supply the joints; in the limbs these
arteries are typically part of a periarticular arterial plexus, which
surrounds the joint ensuring blood flow distal to the joint regardless of theposition assumed by the joint.
The skeletal system receives 5-
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The skeletal system receives 510 % of cardiac output.Individual long bones have 3interactive circulatory
systems all of whichcommunicate in an adult.
In children the metaphyseal-epiphyseal system separates
when the ossific nucleus isformed.
1. Nutrient artery system2. Metaphyseal-epiphyseal
system
3. Periosteal system ( low
pressure system)
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Nutrient artery system-high pressure
system A major artery of the systemic
circulation enters the mid-diaphysis through a nutrientforamen. Once in the medullarycanal , it divides into ascendingand descending arteries whichanastomose with metaphysealvessels and directly penetratethe endosteal surface,supplyingthe inner 2/3 rds of the cortex.
In the child these vessels end onthe metaphyseal side of thephysis,contributing to theprocess of endochondralossification.
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Metaphyseal-epiphyseal system
The periarticular vascular complex penetratesthe thin cortex and supplies the metaphysis,physis and epiphysis. The metaphyseal vesselsanastomose with the medullary and
epiphyseal arteries after growth plate fusion.
In epiphyses with large articular surfaces, suchas radial and femoral heads, vessels enter the
bone between the articular cartilage and thephysis, making the blood supply relativelytenuous.
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Periosteal system(low pressure system)
Capillaries enter at the sites of major muscle
attachments, normally supplying the outer
third of the cortex. This is the dominant
system in the child and is responsible forcircumferential growth.
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these 3 systems are interconnected, and each is able to become dominantsupply if another is damaged. The normal direction of flow iscentrifugal ( inside to out) but if endosteal system is damaged theperiosteal system becomes dominant and the flow becomes centripetal( outside to in).
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Large irregular bones, short bones, and flat bones
These bones receive a superficial blood supplyfrom the periosteum, as well as frequently fromlarge nutrient arteries that penetrate directly intothe medullary bone. The 2 systems anastomosefreely.
Venous and Lymphatic Drainage of Bone
Blood is drained from bone through veins thataccompany the arteries and frequently leavesthrough foramina near the articular ends of thebones. Lymph vessels are abundant in theperiosteum.
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Veins accompany arteries through the nutrientforamina. Lymphatic vessels are abundant in theperiosteum.
Nerves accompany blood vessels supplying thebones. The periosteum is richly supplied withsensory nerves-periosteal nerves that carry painfibres. Within bones, vasomotor nerves cause
constriction or dilation of blood vessels,regulating blood flow through bone marrow.
Classification of joints
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Classification of joints
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Blood supply of joints
Joints receive blood from
articular arteries that arise
from the vessels around the
joint. The arteries often
anastomose to form networks( periarticular arterial
anastomoses) to ensure blood
supply to and across the jointin the various positions
assumed by the joints.
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Synovial joints include:-
Plane joints
Hinge joints
Saddle joints
Condyloid joints
Ball and socket joints
Pivot joints
Synovial joints are also associated
with bursae, which are flattenedfibrous sacs lined with synovial
membrane that develop in areas
of friction. Tendon sheaths are
special bursae that wrap around
tendons in areas of friction.
Synovial fluid
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All freely moveable joints have some synovial fluid in them. Synovial fluid originates
from plasma that is filtered by the capillary net and diffuses into the knee along with
hyaluronic acid, which is locally synthesized. Synovial fluid transports nutrients, assists
in the joint's defense, and lubricates the joint.
Blood supply to knee joint
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Blood supply to knee joint
Blood supply to skin around the knee
is random (as opposed to axial)
- intrinsic contributors to skin
overlying knee are perforating branches
of the superior and inferior genicular
systems;
- extrinsic supply: 3 sources;
Descending genicular
Recurrent branch of anterior tibial
artery
Descending branch of the lateralfemorartery;
Pediatric Bone Circulation:
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Pediatric Bone Circulation:
Circulation in pediatric bone:
- differs from adult circulation due torequirements of growth & presence of
epiphyseal plate
- terminal branches of nutrient artery, along
with metaphyseal vessels, approach growthplate in a parallel relationship
- branches are so numerous as they reach
growth plate that there is almost one vessel
for each column of cartilage cells
- in final few mm before terminal
arteriole reaches cartilage, it is encased in a
tube of enchondral bone
as vessel extends to end of cartilage
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as vessel extends to end of cartilagecolumn, it makes abrupt 180 deg turnto enter larger venule
- slowing of the circulation maypermit lodging & proliferation ofbacteria to produce focus ofhematogenous osteomyelitis
- function of metaphyseal blood
supply(metaphyseal side of growthplate) is to provide nutrition for activecells involved in endochondralossification
- epiphyseal vessels are essential for
they supply dividing cells of growthplate & hence are responsible formaintaining longitudinal bone growth
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References
Basic Orthopaedic Sciences ( The Stanmore
guide) by Manoj Ramachandran
Apleys System of orthopaedics and fractures
Clinically oriented anatomy
Grays anatomy for students
Wheeless textbook oforthopaedics www.emedicine.medscape.com