Fractures and fracture healing

FRACTURES ANDFRACTURES AND
FRACTURE HEALINGFRACTURE HEALING
DR.JAYANT SHARMADR.JAYANT SHARMA
M.S., D.N.B., M.N.A.M.S.M.S., D.N.B., M.N.A.M.S.
CONSULTANT ORTHOPAEDICS AND SPORTSCONSULTANT ORTHOPAEDICS AND SPORTS
MEDICINEMEDICINE
ARIHANT HOSPITALARIHANT HOSPITAL
INDOREINDORE

BONESBONES
 Bones are surprisingly light, accounting forBones are surprisingly light, accounting for
only 14% of total body weight. Bones areonly 14% of total body weight. Bones are
a storehouse of minerals. They hold 99%a storehouse of minerals. They hold 99%
of the body’s calcium, 86% of itsof the body’s calcium, 86% of its
Phosphate, and 54% of Magnesium.Phosphate, and 54% of Magnesium.

PeriosteumPeriosteum
The Periosteum is composed of an innerThe Periosteum is composed of an inner
cambium layer that is immediately adjacent tocambium layer that is immediately adjacent to
the bone surface and an outer dense fibrousthe bone surface and an outer dense fibrous
layer.layer.
 Cambium layer consists of osteoprogenitor cells.consists of osteoprogenitor cells.
 These are flat and spindle shaped and areThese are flat and spindle shaped and are
capable of differentiating into osteoblasts andcapable of differentiating into osteoblasts and
forming bones in response to variousforming bones in response to various
stimulationsstimulations

 The periosteum is thick and looselyThe periosteum is thick and loosely
attached to the cortex in children, but it isattached to the cortex in children, but it is
thinner and more adherent in adults.thinner and more adherent in adults.
 The periosteum carries a dense networkThe periosteum carries a dense network
of blood, lymphatic vessels, andof blood, lymphatic vessels, and
predominantly sensory nerves forpredominantly sensory nerves for
maintenance of the bone structuremaintenance of the bone structure

 The periosteum completely covers a bone,The periosteum completely covers a bone,
except in the region of the articularexcept in the region of the articular
cartilage and at sites of musclecartilage and at sites of muscle
attachments. It is somewhat anchored toattachments. It is somewhat anchored to
the cortex by Sharpey fibers that penetratethe cortex by Sharpey fibers that penetrate
into the bone.into the bone.

Different patterns of periosteal stimulation result inDifferent patterns of periosteal stimulation result in
different patterns of periosteal bone formation.different patterns of periosteal bone formation.
 Continual insultContinual insult results in streams of periostealresults in streams of periosteal
bone that are perpendicular to the bone surface,bone that are perpendicular to the bone surface,
resulting in a hair-on-end appearance onresulting in a hair-on-end appearance on
radiographs.radiographs.
 Intermittent periosteal stimulationIntermittent periosteal stimulation results inresults in
multiple partially separated streams of periostealmultiple partially separated streams of periosteal
bone, parallel to the bone surface, giving anbone, parallel to the bone surface, giving an
onionskin appearance on radiographsonionskin appearance on radiographs

Periosteum
A very
important
source of
bone
forming
cells

EndosteumEndosteum
 The endosteum is composed ofThe endosteum is composed of
osteoprogenitor cells and only a smallosteoprogenitor cells and only a small
amount of connective tissue.amount of connective tissue.
 Covering the surface of bone trabeculaeCovering the surface of bone trabeculae
and the medullary surface of cortical boneand the medullary surface of cortical bone
and haversian canals. and haversian canals.
 The endosteum serves as one of theThe endosteum serves as one of the
functional surfaces for bone remodelingfunctional surfaces for bone remodeling

Periosteum
Endosteum
Bone marrow
Other sites

TYPES OF BONE TISSUETYPES OF BONE TISSUE
 Bone tissue can be classified in severalBone tissue can be classified in several
ways, includingways, including
 texture,texture,
 matrix arrangement,matrix arrangement,
 maturity, andmaturity, and
 developmental origin.developmental origin.

Types of bone tissueTypes of bone tissue
Based on texture of cross sections,
bone tissue can be classified as
follows::
 Compact boneCompact bone (dense bone, cortical bone): Compact(dense bone, cortical bone): Compact
bone is ivorylike and dense in texture without cavities.bone is ivorylike and dense in texture without cavities.
It is the shell of many bones and surrounds theIt is the shell of many bones and surrounds the
trabecular bone in the center. Compact bone consiststrabecular bone in the center. Compact bone consists
mainly of haversian systems ormainly of haversian systems or secondary osteons..
 Sponge boneSponge bone (trabecular bone, cancellous bone):(trabecular bone, cancellous bone):
Sponge bone is so named because it is spongelikeSponge bone is so named because it is spongelike
with numerous cavities. It is located within thewith numerous cavities. It is located within the
medullary cavity and consists of extensively connectedmedullary cavity and consists of extensively connected
bony trabeculae that are oriented along the lines ofbony trabeculae that are oriented along the lines of
stressstress..

 In contrast to compact bone, completeIn contrast to compact bone, complete
osteons are usually absent in sponge boneosteons are usually absent in sponge bone
due to the thinness of the trabeculae. Spongedue to the thinness of the trabeculae. Sponge
bone is also more metabolically active thanbone is also more metabolically active than
compact bone because of its much largercompact bone because of its much larger
surface area for remodelingsurface area for remodeling

Based on MaturityBased on Maturity
 Immature boneImmature bone (primary bone tissue):(primary bone tissue):
Immature bone is woven bone.Immature bone is woven bone.
 Mature boneMature bone (secondary bone tissue) :(secondary bone tissue) :
Mature bone is characteristically lamellarMature bone is characteristically lamellar
bone. Almost all bones in adults arebone. Almost all bones in adults are
lamellar bones.lamellar bones.

WOVEN BONEWOVEN BONE
The earliest bone to be laid
Down
. Its histological structure
shows the fibrils to be
randomly
Distributed
it is also known
as immature bone.
A feature of
immature bone is that it
contains a relatively higher
proportion of osteocytes.

Woven bone (primary bone tissue)Woven bone (primary bone tissue)
 It has the collagen fibers are arranged inIt has the collagen fibers are arranged in
irregular random arrays.irregular random arrays.
 contain smaller amounts of mineral substancecontain smaller amounts of mineral substance
and a higher proportion of osteocytes thanand a higher proportion of osteocytes than
lamellar bone.lamellar bone.
 It is temporary, eventually converted to lamellarIt is temporary, eventually converted to lamellar
bone;bone;
 This type of bone is also pathologic tissue inThis type of bone is also pathologic tissue in
adults.adults.
 Except in a few places, such as areas nearExcept in a few places, such as areas near
the sutures of the flat bones of the skull, tooththe sutures of the flat bones of the skull, tooth
sockets , and the insertion site of some tendonssockets , and the insertion site of some tendons

Lamellar bone (secondary boneLamellar bone (secondary bone
tissue):tissue):
 It is a mature bone with collagen fibersIt is a mature bone with collagen fibers
that are arranged in lamellae.that are arranged in lamellae.
 In contrast to sponge bone, in compactIn contrast to sponge bone, in compact
bone, the lamellae are concentricallybone, the lamellae are concentrically
organized around a vascular canal,organized around a vascular canal,
termed a haversian canal.termed a haversian canal.

Lamellar Bone
Mature bone, alternatively
described as lamellar bone,
is
characterized by the
comparatively regular
arrangement of its lamellae
and the presence of fewer
osteocytes which are more
evenly arranged and are
present in flat lacunae.

Based on developmental origin,Based on developmental origin,
 Intramembranous bone (mesenchymal bone):Intramembranous bone (mesenchymal bone):
Intramembranous bone develops from directIntramembranous bone develops from direct
transformation of condensed mesenchyme. Flattransformation of condensed mesenchyme. Flat
bones are formed in this way.bones are formed in this way.
 Intracartilaginous bone (cartilage bone,Intracartilaginous bone (cartilage bone,
endochondral bone):endochondral bone): Intracartilaginous boneIntracartilaginous bone
forms by replacing a reformed cartilage model.forms by replacing a reformed cartilage model.
Long bones are formed in this wayLong bones are formed in this way

Microscopic architecture of boneMicroscopic architecture of bone
 Haversian systemHaversian system (secondary osteon)(secondary osteon)
 The primary structural unit of compact bone.The primary structural unit of compact bone.
 Each is a long, often bifurcated, cylinder that isEach is a long, often bifurcated, cylinder that is
parallel to the long axis of bone, formed byparallel to the long axis of bone, formed by
successive deposition of 4-20 (average 6) concentricsuccessive deposition of 4-20 (average 6) concentric
layers of lamellae.layers of lamellae.
 Collagen fibers are parallel to each other within eachCollagen fibers are parallel to each other within each
lamella,and they are oriented perpendicularly to thelamella,and they are oriented perpendicularly to the
fibers in the neighboring lamellae.fibers in the neighboring lamellae.

 The haversian canals connect with each otherThe haversian canals connect with each other
by transverse or oblique Volkmann canals.by transverse or oblique Volkmann canals.
 These communicate with the marrow cavity andThese communicate with the marrow cavity and
the periosteum to provide channels for thethe periosteum to provide channels for the
neurovascular system.neurovascular system.
 Volkmann canals are not surrounded byVolkmann canals are not surrounded by
concentric lamellae; rather, they perforate theconcentric lamellae; rather, they perforate the
lamellae.lamellae.

Interstitial lamellaeInterstitial lamellae
 Interstitial lamellaeInterstitial lamellae are incomplete or fragmentedare incomplete or fragmented
osteons that are located between the secondaryosteons that are located between the secondary
osteons.osteons.
 They represent the remnant osteons left from partialThey represent the remnant osteons left from partial
resorption of old osteons during bone remodeling.resorption of old osteons during bone remodeling.
 The mixture of interstitial lamellae and complete osteonsThe mixture of interstitial lamellae and complete osteons
produces aproduces a mosaic patternmosaic pattern..
 Thus, the age of the bone can be deduced from theThus, the age of the bone can be deduced from the
proportion of interstitial lamellae and intact osteons.proportion of interstitial lamellae and intact osteons.
 Younger bone has more complete osteons and lessYounger bone has more complete osteons and less
interstitial lamellae in between the osteons.interstitial lamellae in between the osteons.

 Lamellar deposition starts from the periphery,Lamellar deposition starts from the periphery,
so that younger lamellae are closer to theso that younger lamellae are closer to the
center of the system, and the youngercenter of the system, and the younger
systems have larger canals.systems have larger canals.
 Between the lamellae are lacunae that containBetween the lamellae are lacunae that contain
the cell bodies and canaliculi that hold thethe cell bodies and canaliculi that hold the
cytoplasmic processes of osteocytes.cytoplasmic processes of osteocytes.

 The age of bone also affects osteoclastThe age of bone also affects osteoclast
activity in bone resorption.activity in bone resorption.
 Osteoclasts preferentially differentiate andOsteoclasts preferentially differentiate and
resorb bone on aged bone than they do onresorb bone on aged bone than they do on
young boneyoung bone
Henriksen et alHenriksen et al,,

Circumferential lamellaeCircumferential lamellae
 Circumferential lamellaeCircumferential lamellae are circularare circular
lamellae that line the external surface oflamellae that line the external surface of
the cortex adjacent to the periosteum andthe cortex adjacent to the periosteum and
line the inner surface of the cortex next toline the inner surface of the cortex next to
the endosteum.the endosteum.
 There are more outer than innerThere are more outer than inner
circumferential lamellae.circumferential lamellae.

ENDOTHELIALENDOTHELIAL
CELLSCELLS
Cells on the surfaces of
blood
vessels
Synthesize Type IV
collagen and
VEGF
has much more active
roles in
events such as
angiogenesis,
wound repair and bone
formaton.

OsteocytesOsteocytes
 An osteoblast becomes an osteocyte when theAn osteoblast becomes an osteocyte when the
cell is encased by osteoid matrix.cell is encased by osteoid matrix.
 It synthesizes itself. Lacunae and canaliculiIt synthesizes itself. Lacunae and canaliculi
form around the osteocyte and its cytoplasmicform around the osteocyte and its cytoplasmic
processes, respectively.processes, respectively.
 An osteocyte lies in its own lacuna and contactsAn osteocyte lies in its own lacuna and contacts
its neighboring osteocytes cytoplasmicallyits neighboring osteocytes cytoplasmically
through canaliculithrough canaliculi

 The processes of adjacent cells makeThe processes of adjacent cells make
contact via gap junctions, maintaining thecontact via gap junctions, maintaining the
vitality of osteocytes by passing nutrientsvitality of osteocytes by passing nutrients
and metabolites between blood vesselsand metabolites between blood vessels
and distant osteocytes, regulating ionand distant osteocytes, regulating ion
homeostasis, and transmitting electricalhomeostasis, and transmitting electrical
signals in bone.signals in bone.

 Osteocytes have reduced synthetic activity andOsteocytes have reduced synthetic activity and
are not capable of mitotic division.are not capable of mitotic division.
 They are actively involved with the maintenanceThey are actively involved with the maintenance
of the bony matrix.of the bony matrix.
 Some of the osteocytes die during remodeling,Some of the osteocytes die during remodeling,
 but most, return to the state of osteoprogenitorbut most, return to the state of osteoprogenitor
cells or persist as osteocytes for a long timecells or persist as osteocytes for a long time

OSTEOBLAS
T
Each active osteoblast has eccentrically
located nuclei with a conspicuous nucleus
and a perinuclear halo, resembling a
plasma cell. However, the osteoblast does
not exhibit the clock-face or wheel-like
chromatin pattern that is seen in a plasma
cell.

 Active osteoblasts depositing osteoid onActive osteoblasts depositing osteoid on
the surface of a woven bone trabecula.the surface of a woven bone trabecula.
 Osteoblasts are columnar or cuboidalOsteoblasts are columnar or cuboidal
shaped, with eccentric nuclei andshaped, with eccentric nuclei and
perinuclear halo.perinuclear halo.
 These cells also have polarity, with theThese cells also have polarity, with the
cytoplasm toward the bone but the nucleicytoplasm toward the bone but the nuclei
at the end away from the bone.at the end away from the bone.

 multinucleated
cells
 largely
responsible for
bone resorption
 Positive for
Tartrate resistant
acid phosphatase
OSTEOCLAST

OsteoclastsOsteoclasts
 They are probably derived from a monocytic-macrophage systemThey are probably derived from a monocytic-macrophage system
and are responsible for bone resorption.and are responsible for bone resorption.
 They are multinucleated cells with fine, fingerlike cytoplasmicThey are multinucleated cells with fine, fingerlike cytoplasmic
processes and are rich in lysosomes that contain tartrate-resistantprocesses and are rich in lysosomes that contain tartrate-resistant
acid phosphatase (TRAP).acid phosphatase (TRAP).
 lie in resorption craters known aslie in resorption craters known as Howship lacunaeHowship lacunae on boneon bone
surfaces or in deep resorption cavities calledsurfaces or in deep resorption cavities called Cutting conesCutting cones..
 These bone cells can only resorb mineralized bone matrix.These bone cells can only resorb mineralized bone matrix.
 Cells that express the full morphologic and functional properties ofCells that express the full morphologic and functional properties of
mature osteoclasts are known to be restricted to the surfaces ofmature osteoclasts are known to be restricted to the surfaces of
bones.(transmigration)bones.(transmigration)

 These transmigration on the bone surfaceThese transmigration on the bone surface
has been assumed to be for the purposehas been assumed to be for the purpose
of bone resorption.of bone resorption.
 Transmigration through bone tissues ofTransmigration through bone tissues of
various cell types results in bone diseasesvarious cell types results in bone diseases
with an imbalance in bone remodeling thatwith an imbalance in bone remodeling that
is caused by excessive osteoclastis caused by excessive osteoclast
resorption.resorption.

 Research is also under way to investigateResearch is also under way to investigate
whether "components of the bone matrixwhether "components of the bone matrix
and specific cell surface receptors onand specific cell surface receptors on
osteoclasts and their precursors play anosteoclasts and their precursors play an
essential role in determining the geneticessential role in determining the genetic
profile and functional properties of fullyprofile and functional properties of fully
differentiated resorbing osteoclastsdifferentiated resorbing osteoclasts

 Osteoclasts or their committed precursors do not haveOsteoclasts or their committed precursors do not have
receptors for parathyroid hormone.receptors for parathyroid hormone.
 The hormonal signal is mediated by osteoblasts.The hormonal signal is mediated by osteoblasts.
 However, osteoclasts do have receptors for calcitonin.However, osteoclasts do have receptors for calcitonin.
 When in an active state, osteoclasts create an effect thatWhen in an active state, osteoclasts create an effect that
always predominates over that of osteoblasts becausealways predominates over that of osteoblasts because
osteoclasts are three times more efficient at boneosteoclasts are three times more efficient at bone
resorption than osteoblasts are at bone deposition.resorption than osteoblasts are at bone deposition.
 In balance, osteoclasts have a much shorter life spanIn balance, osteoclasts have a much shorter life span
than osteoblasts.than osteoblasts.
 Osteoclasts are rarely seen in routine histologic sectionsOsteoclasts are rarely seen in routine histologic sections
of normal bone.of normal bone.
 An increased number of osteoclasts is characteristic ofAn increased number of osteoclasts is characteristic of
diseases with increased bone turnover.diseases with increased bone turnover.

Bone matrixBone matrix
 Bone matrix consists of organic andBone matrix consists of organic and
inorganic components.inorganic components.
 Gives bone its hardness and resistance.Gives bone its hardness and resistance.
 The organic component is composed ofThe organic component is composed of
collagen fibers with predominately type Icollagen fibers with predominately type I
collagen (95%) and amorphous material,collagen (95%) and amorphous material,
including glycosaminoglycansincluding glycosaminoglycans
 Osteoid is uncalcified organic matrix.Osteoid is uncalcified organic matrix.

 Inorganic matter represents about 50% ofInorganic matter represents about 50% of
the dry weight of bone matrix,the dry weight of bone matrix,
 composed of abundant calcium andcomposed of abundant calcium and
phosphorusphosphorus
 as well as smaller amounts ofas well as smaller amounts of
bicarbonate, citrate, magnesium,bicarbonate, citrate, magnesium,
potassium, and sodium.potassium, and sodium.
 Calcium forms hydroxyapatite crystals withCalcium forms hydroxyapatite crystals with
phosphorus but is also present in anphosphorus but is also present in an
amorphous form.amorphous form.

 During bone remodeling,During bone remodeling,
osteoblasts deposit a layer ofosteoblasts deposit a layer of
osteoid seam (approximately 10osteoid seam (approximately 10
µm thick) on the surface ofµm thick) on the surface of
preexisting bone, which thenpreexisting bone, which then
begins to mineralize inbegins to mineralize in
approximately 20 days. Thisapproximately 20 days. This
interval is known as theinterval is known as the
mineralization lag timemineralization lag time

 In the histology of normal bone, as aIn the histology of normal bone, as a
result of the normal remodelingresult of the normal remodeling
process, up to 20% of the boneprocess, up to 20% of the bone
surface may be covered by osteoidsurface may be covered by osteoid
(usually 10 µm thick).(usually 10 µm thick).

 An increased amount of osteoid isAn increased amount of osteoid is
seen in pathologic conditions inseen in pathologic conditions in
which the remodeling rate iswhich the remodeling rate is
accelerated or in which theaccelerated or in which the
mineralization lag time is increasedmineralization lag time is increased

Blood supply to bone
Bone cells is less
than
20 um away from a
blood vessel
70% of the blood
supply to cortex are
from nutrient arteries
Compensate from the
periosteal arteries in

Blood supply of boneBlood supply of bone
 Long bones
 Diaphyseal nutrient artery::

This is the most important supply of arterialThis is the most important supply of arterial
blood to a long bone.blood to a long bone.
 One or 2 principal diaphyseal nutrient arteriesOne or 2 principal diaphyseal nutrient arteries
first pass obliquely through the cortical bone.first pass obliquely through the cortical bone.
 These arteries then divide into ascending andThese arteries then divide into ascending and
descending branches and supply the inner twodescending branches and supply the inner two
thirds of the cortex and medullary cavity.thirds of the cortex and medullary cavity.

 Metaphyseal and epiphyseal arteries : Numerous: Numerous
metaphyseal and epiphyseal arteries supply themetaphyseal and epiphyseal arteries supply the
ends of bones.ends of bones.
 These blood vessels mainly arise from theThese blood vessels mainly arise from the
arteries that supply the adjacent joint,arteries that supply the adjacent joint,
anastomose with the diaphyseal capillaries, andanastomose with the diaphyseal capillaries, and
terminate interminate in bone marrowbone marrow, cortical bone,, cortical bone,
trabecular bone, and articular cartilage.trabecular bone, and articular cartilage.
 In growing bones, these arteries are separatedIn growing bones, these arteries are separated
by the epiphyseal cartilaginous plates.by the epiphyseal cartilaginous plates.
 Periosteal arterioles : Several of these vessels: Several of these vessels
supply the outer layers of corticalsupply the outer layers of cortical bonebone

 Large irregular bones, short bones, and flatLarge irregular bones, short bones, and flat
bonesbones
 These bones receive a superficial blood supply from theThese bones receive a superficial blood supply from the
periosteum, as well as frequently from large nutrientperiosteum, as well as frequently from large nutrient
arteries that penetrate directly into the medullary bone.arteries that penetrate directly into the medullary bone.
The 2 systems anastomose freely.The 2 systems anastomose freely.
 Venous and lymphatic drainage of boneVenous and lymphatic drainage of bone
 Blood is drained from bone through veins thatBlood is drained from bone through veins that
accompany the arteries and frequently leaves throughaccompany the arteries and frequently leaves through
foramina near the articular ends of the bones. Lymphforamina near the articular ends of the bones. Lymph
vessels are abundant in the periosteum.vessels are abundant in the periosteum.

Nerve supply of boneNerve supply of bone
 Nerves are most rich in the articular extremities of theNerves are most rich in the articular extremities of the
long bones, vertebrae, and larger flat bones.long bones, vertebrae, and larger flat bones.
 Many nerve fibers accompany the blood vessels to theMany nerve fibers accompany the blood vessels to the
interior of the bones and to the perivascular spaces ofinterior of the bones and to the perivascular spaces of
the haversian canals.the haversian canals.
 The periosteal nerves are sensory nerves, some ofThe periosteal nerves are sensory nerves, some of
which arewhich are painpain fibers.fibers.
 Therefore, the periosteum is especially sensitive toTherefore, the periosteum is especially sensitive to
tearingtearing or tension.or tension.
 Accompanying the arteries inside the bones areAccompanying the arteries inside the bones are
vasomotor nerves, which control vascular constrictionvasomotor nerves, which control vascular constriction
and dilationand dilation

EpiphysisEpiphysis
 In the long bones, the epiphysis is theIn the long bones, the epiphysis is the
region between the growth plate or growthregion between the growth plate or growth
plate scar and the expanded end of bone,plate scar and the expanded end of bone,
covered by articular cartilage.covered by articular cartilage.
 An epiphysis in a skeletally matureAn epiphysis in a skeletally mature
person consists of abundant trabecularperson consists of abundant trabecular
bone and a thin shell of cortical bone . bone and a thin shell of cortical bone .

 Although an epiphysis is present at eachAlthough an epiphysis is present at each
end of the long limb bones,end of the long limb bones,
 it is found at only one end of theit is found at only one end of the
metacarpals (proximal first and distalmetacarpals (proximal first and distal
second through the fifth metacarpals),second through the fifth metacarpals),
metatarsals (proximal first and distalmetatarsals (proximal first and distal
second through fifth metatarsals),second through fifth metatarsals),
phalanges (proximal ends), clavicles, andphalanges (proximal ends), clavicles, and
ribs.ribs.

 The epiphysis is the location of secondary ossification centersThe epiphysis is the location of secondary ossification centers
during development.during development.
 The structure of the epiphysis is more complex in bones that areThe structure of the epiphysis is more complex in bones that are
fused from more than one part during development.fused from more than one part during development.
 Examples include the proximal and distal ends of the humerus,Examples include the proximal and distal ends of the humerus,
femur, and vertebrae.femur, and vertebrae.
 The proximal end of the humerus is developed from 3 separateThe proximal end of the humerus is developed from 3 separate
ossification centers, which later coalesce to form a single epiphysealossification centers, which later coalesce to form a single epiphyseal
mass.mass.
 In the proximal humeral epiphysis, one of the centers forms theIn the proximal humeral epiphysis, one of the centers forms the
articular surface, and the other 2 become the greater and lesserarticular surface, and the other 2 become the greater and lesser
tuberosities.tuberosities.
 Carpal bones, tarsal bones, and the patella are also calledCarpal bones, tarsal bones, and the patella are also called
epiphysioid bones and are developmentally equivalent to theand are developmentally equivalent to the
epiphyses of the long bonesepiphyses of the long bones

 Some bone tumors such asSome bone tumors such as
chondroblastomachondroblastoma have a stronghave a strong
predilection for the epiphysis orpredilection for the epiphysis or
epiphysioid bonesepiphysioid bones

MetaphysisMetaphysis
 This is the junctional region between theThis is the junctional region between the
epiphysis and the diaphysis.epiphysis and the diaphysis.
 The metaphysis contains abundant trabecularThe metaphysis contains abundant trabecular
bone, but the cortical bone thins here relative tobone, but the cortical bone thins here relative to
the diaphysis.the diaphysis.
 This region is a common site for many primaryThis region is a common site for many primary
bone tumors and similar lesions. The relativebone tumors and similar lesions. The relative
predilection ofpredilection of osteosarcomaosteosarcoma..
 for the metaphyseal region of long bones infor the metaphyseal region of long bones in
children has been attributed to the rapid bonechildren has been attributed to the rapid bone
turnover due to extensive bone remodelingturnover due to extensive bone remodeling
during growth spurtsduring growth spurts

OSSIFICATIONOSSIFICATION
 Bone tissue arises byBone tissue arises by IntramembranousIntramembranous
ossification or by Endochondral ossificationossification or by Endochondral ossification..
 In either case, the original or model tissue isIn either case, the original or model tissue is
gradually destroyed and replaced with bonegradually destroyed and replaced with bone
tissue.tissue.
 Bone forms only by appositional deposition ofBone forms only by appositional deposition of
matrix on the surface of a preformed tissue.matrix on the surface of a preformed tissue.
 Woven bone is initially formed and is then laterWoven bone is initially formed and is then later
converted to lamellar bone by subsequentconverted to lamellar bone by subsequent
remodeling.remodeling.

Intramembranous ossificationIntramembranous ossification
 Although it is the source of flat bones, thisAlthough it is the source of flat bones, this
process also contributes to the growth of shortprocess also contributes to the growth of short
bones and thickening of long bones.bones and thickening of long bones.
 Interstitial membranous ossification takes placeInterstitial membranous ossification takes place
within a condensation of mesenchymal tissue.within a condensation of mesenchymal tissue.
 The process begins when multiple groups ofThe process begins when multiple groups of
cells differentiate into osteoblasts in a primarycells differentiate into osteoblasts in a primary
ossification center.ossification center.
 Osteoid is synthesized and then mineralizedOsteoid is synthesized and then mineralized
surrounding the osteoblasts, which then becomesurrounding the osteoblasts, which then become
osteocytes.osteocytes.

 When these ossification centers fuse, aWhen these ossification centers fuse, a
loose trabecular structure known asloose trabecular structure known as
primary spongiosa is formed.primary spongiosa is formed.
 Subsequently, blood vessels grow intoSubsequently, blood vessels grow into
the connective tissue between thethe connective tissue between the
trabeculae.trabeculae.
 Bone marrow stem cellsBone marrow stem cells from thefrom the
circulating blood then give rise tocirculating blood then give rise to
hematopoietic cells.hematopoietic cells.

Intramembranous ossificationIntramembranous ossification
 .. Woven bone arises directly from the surroundingWoven bone arises directly from the surrounding
mesenchymal tissuemesenchymal tissue

 GrowthGrowth and fusion of several ossification centersand fusion of several ossification centers
eventually replace the original mesenchymaleventually replace the original mesenchymal
tissue.tissue.
 In flat bones, compact bone is formed at bothIn flat bones, compact bone is formed at both
the internal and external surfacesthe internal and external surfaces
 marked predominance of bone deposition overmarked predominance of bone deposition over
bone resorption, whereas a spongy patternbone resorption, whereas a spongy pattern
remains in the central portion.remains in the central portion.
 The endosteum and periosteum are formed fromThe endosteum and periosteum are formed from
layers of connective tissue that are notlayers of connective tissue that are not
undergoing ossificationundergoing ossification

Endochondral ossificationEndochondral ossification
 Endochondral ossification is responsibleEndochondral ossification is responsible
for the formation of the short and longfor the formation of the short and long
bones. bones.
 This process takes place within a hyalineThis process takes place within a hyaline
cartilage model, which provides a templatecartilage model, which provides a template
of the shape of the bone to be formed.of the shape of the bone to be formed.

Endochondral ossificationEndochondral ossification
 It can be divided into 2 phases.It can be divided into 2 phases.
 First phase: Chondrocytes of the model: Chondrocytes of the model
are hypertrophic and degenerated, andare hypertrophic and degenerated, and
then the intervening chondroid matrix isthen the intervening chondroid matrix is
calcified.calcified.
 Second phase:Second phase: osteogenic buds,osteogenic buds,
composed of osteoprogenitor cells andcomposed of osteoprogenitor cells and
blood capillaries, invade the spaces left byblood capillaries, invade the spaces left by
the degenerating chondrocytesthe degenerating chondrocytes

 Osteoblasts arise from osteoprogenitor cells andOsteoblasts arise from osteoprogenitor cells and
lay down a layer of rapidly mineralized osteoidlay down a layer of rapidly mineralized osteoid
on the surface of calcified cartilage.on the surface of calcified cartilage.
 The complex structure of calcified cartilage withThe complex structure of calcified cartilage with
overlying newly bone thus formed is known asoverlying newly bone thus formed is known as
the primary spongiosa,the primary spongiosa,
 which is later remodelled to become lamellarwhich is later remodelled to become lamellar
bone (secondary spongiosa).bone (secondary spongiosa).

 Calcified cartilage remnants are resorbedCalcified cartilage remnants are resorbed
by chondroclasts,by chondroclasts,
 which are structurally and functionallywhich are structurally and functionally
equivalent to osteoclasts, exceptequivalent to osteoclasts, except
that chondroclasts work on cartilage ratherthat chondroclasts work on cartilage rather
than bone.than bone.
 Thus, the cartilage model is graduallyThus, the cartilage model is gradually
replaced by bone and marrow cavitiesreplaced by bone and marrow cavities

Long bones are formed from cartilaginous modelsLong bones are formed from cartilaginous models..
 The primary ossification center is initiatedThe primary ossification center is initiated
by intramembranous ossificationby intramembranous ossification
 that is produced by the deep portions ofthat is produced by the deep portions of
the perichondrium that surround thethe perichondrium that surround the
diaphysis.diaphysis.
 A bone collar is thus formed, blocking theA bone collar is thus formed, blocking the
nutrient diffusion and leading to thenutrient diffusion and leading to the
degeneration of internal chondrocytes.degeneration of internal chondrocytes.

 The perichondrium then becomes theThe perichondrium then becomes the
periosteum, from which the osteogenicperiosteum, from which the osteogenic
bud arises and penetrates the calcifiedbud arises and penetrates the calcified
cartilage matrix through passages thatcartilage matrix through passages that
are created in the bone collar byare created in the bone collar by
osteoclastsosteoclasts

 The primary ossification center expandsThe primary ossification center expands
longitudinally and is associated with thelongitudinally and is associated with the
growth of the periosteal bone collar.growth of the periosteal bone collar.
 Osteoclasts are activated at the beginningOsteoclasts are activated at the beginning
of the process, resorb the bone at theof the process, resorb the bone at the
center, and hence create the marrowcenter, and hence create the marrow
cavity.cavity.

 At a later stage of bone development, aAt a later stage of bone development, a
secondary ossification center arises at thesecondary ossification center arises at the
center of each epiphysis.center of each epiphysis.
 Unlike primary ossification, whichUnlike primary ossification, which
expands in a longitudinal fashion, theexpands in a longitudinal fashion, the
secondary ossification center grows in asecondary ossification center grows in a
radial fashionradial fashion

 Furthermore, a bone collar is not formed inFurthermore, a bone collar is not formed in
the area of articular cartilage due to thethe area of articular cartilage due to the
absence of perichondrium in this area.absence of perichondrium in this area.
 Thus, the epiphysis of the chondroidThus, the epiphysis of the chondroid
model is replaced by bone tissue, exceptmodel is replaced by bone tissue, except
the articular cartilage and the epiphysealthe articular cartilage and the epiphyseal
cartilage.cartilage.

Epiphyseal cartilageEpiphyseal cartilage
 It is located between the epiphysis and the metaphysis and isIt is located between the epiphysis and the metaphysis and is
responsible for the longitudinal growth of bone. It can be divided intoresponsible for the longitudinal growth of bone. It can be divided into
5 zones, starting from the epiphyseal side of cartilage, as follows:5 zones, starting from the epiphyseal side of cartilage, as follows:
 Resting zone – This zone consists of small chondrocytes.
 Proliferative zone – The proliferative zone consists of rapidly
dividing chondrocytes in columns that are parallel to the long axis of
the bone, resulting in interstitial growth of cartilage. The chondroid
matrix is laid down, and mitotic figures may be detected.
 Hypertrophic zone – This zone consists of large chondrocytes
that contain abundant cytoplasmic glycogen. In the hypertrophic
zone, chondrocytes mature and degenerate, with associated
chondroid matrix resorption.

Calcified cartilage zone
(zone of provisional
calcification) – This zone is
where chondrocytes die.
Chondrocyte death is
followed by blood vessel
invasion and bone deposition
on the calcified cartilage.
Ossification zone – The
ossification zone is where
primary spongiosa forms by
rapidly mineralized osteoid
that is laid down on the
calcified cartilage septa

RemodellingRemodelling
 is a continuous process throughout life, inis a continuous process throughout life, in
which damaged bone is repaired, ionwhich damaged bone is repaired, ion
homeostasis is maintained, and bone ishomeostasis is maintained, and bone is
reinforced for increased stress.reinforced for increased stress.
 In adults, the remodeling rate varies inIn adults, the remodeling rate varies in
different types of bones.different types of bones.
 Trabecular bone is remodeled at a higherTrabecular bone is remodeled at a higher
rate (25% per year) than that of corticalrate (25% per year) than that of cortical
bone (3% per year) in a healthy adult.bone (3% per year) in a healthy adult.

Resorption and Deposition
 Normally balanced, and bone density is maintained.Normally balanced, and bone density is maintained.
 A lytic lesion results when resorptive activity exceedsA lytic lesion results when resorptive activity exceeds
deposition activity in a pathologic state.deposition activity in a pathologic state.
 TheThe cement linecement line (reversal line) is evidence of previous(reversal line) is evidence of previous
remodeling activity and is formed by filling of new bone inremodeling activity and is formed by filling of new bone in
a previously resorbed cavitya previously resorbed cavity
 The cement line is strongly basophilic due to the highThe cement line is strongly basophilic due to the high
content of inorganic matrix and is normally found in thecontent of inorganic matrix and is normally found in the
haversian and interstitial systems of adult bone.haversian and interstitial systems of adult bone.
 The relative amount of cement lines corresponds to theThe relative amount of cement lines corresponds to the
amount of remodeling that has occurred.amount of remodeling that has occurred.

 An entire remodeling cycle requiresAn entire remodeling cycle requires
approximately 6 months.approximately 6 months.
 Although a cement line that results fromAlthough a cement line that results from
normal remodeling is relatively long andnormal remodeling is relatively long and
straight.straight.
 an indented or mosaic pattern indicates aan indented or mosaic pattern indicates a
pathologically accelerated remodelingpathologically accelerated remodeling
processprocess

DEFINITIONDEFINITION
 FRACTUREFRACTURE IS DEFINED AS ANYIS DEFINED AS ANY
BREAK IN THE CONTINUITY OFBREAK IN THE CONTINUITY OF
THE BONE.IT IS USUALLY DUE TOTHE BONE.IT IS USUALLY DUE TO
DIRECT OR INDIRECT TRAUMA.DIRECT OR INDIRECT TRAUMA.
 A FRACTURE OCCURING IN AA FRACTURE OCCURING IN A
DISEASED BONE IS CONSIDEREDDISEASED BONE IS CONSIDERED
AS AAS A PATHOLOGICAL FRACTUREPATHOLOGICAL FRACTURE

Fracture FactsFracture Facts
Fractures, or broken bones, are extremelyFractures, or broken bones, are extremely
common. Approximately 6.8 millioncommon. Approximately 6.8 million
Americans break a bone each year. OnAmericans break a bone each year. On
average, every person in the Unitedaverage, every person in the United
States will experience two broken bonesStates will experience two broken bones
over the course of a lifetime. over the course of a lifetime.

How Do Bones Break?How Do Bones Break?

Bones are made up of bone cells, proteins, andBones are made up of bone cells, proteins, and
minerals. Although bones are amazingly tough -minerals. Although bones are amazingly tough -
one cubic inch can withstand loads of almostone cubic inch can withstand loads of almost
19,000 pounds, about four times the strength of19,000 pounds, about four times the strength of
concrete – they can still break. Like a woodenconcrete – they can still break. Like a wooden
pencil, bones can bend to a certain extent,pencil, bones can bend to a certain extent,
however, once the pressure is too much or toohowever, once the pressure is too much or too
sudden, bones might break, or fracture. sudden, bones might break, or fracture.

FRACTURE CLASSIFICATIONFRACTURE CLASSIFICATION
 SIMPLE OR CLOSEDSIMPLE OR CLOSED::
A FRACTURE WHICH DOES NOTA FRACTURE WHICH DOES NOT
COMMUNICATE WITH THE EXTERIOR.COMMUNICATE WITH THE EXTERIOR.
 OPEN OR COMPOUND FRACTUREOPEN OR COMPOUND FRACTURE ::
FRACTURE WHICH COMMUNICATESFRACTURE WHICH COMMUNICATES
WITH THE EXTERIOR THROUGH AWITH THE EXTERIOR THROUGH A
WOUND.WOUND.

TERMINOLOGYTERMINOLOGY
 TRANSVERSETRANSVERSE
 OBLIQUEOBLIQUE
 SPIRALSPIRAL
 COMMINUTED-- MORE THAN TWO PEICESCOMMINUTED-- MORE THAN TWO PEICES
 SEGMENTAL—FRACTURES AT TWO LEVELSSEGMENTAL—FRACTURES AT TWO LEVELS
 INCOMPLETEINCOMPLETE
 GREENSTICK—NO DISCONTINUITY ASGREENSTICK—NO DISCONTINUITY AS
PERIOSTEUM INTACT SEEN IN SOFT BONESPERIOSTEUM INTACT SEEN IN SOFT BONES
OF CHILDRENOF CHILDREN
 COMPRESSIONCOMPRESSION

DISPLACEMENTSDISPLACEMENTS
 LATERALLATERAL
 ANGULARANGULAR
 ANTEROPOSTERIORANTEROPOSTERIOR
 ROTATIONROTATION

DIAGNOSISDIAGNOSIS
 HISTORYHISTORY
 PROTECTIVE MUSCLE SPASMPROTECTIVE MUSCLE SPASM
 OEDEMAOEDEMA
 WARMTHWARMTH
 CREPITUSCREPITUS
 DEFORMITYDEFORMITY
 X-RAYX-RAY

 Extracellular matrix formation during
 fracture healing
 Type III collagen -- inflammatory stage
 Type II collagen -- cartilaginous phase
 Type IX collagen -- chondrogenesis
 Type X collagen -- hypertrophic
chondrocytes
 Type I collagen -- ossification and
remodeling stages.

HEALING OF FRACTURESHEALING OF FRACTURES
 HEALING OF A FRACTUREHEALING OF A FRACTURE
OCCURS IN THREE PHASES:OCCURS IN THREE PHASES:
 A)INFLAMMATORY PHASE.A)INFLAMMATORY PHASE.
 B) CELLULAR PROLIFERATIONB) CELLULAR PROLIFERATION
 C)REMODELLING PHASE.C)REMODELLING PHASE.

INFLAMMATORY PHASEINFLAMMATORY PHASE
 AS THE BONE BREAKS THEREAS THE BONE BREAKS THERE
OCCURS BLEEDING AT THEOCCURS BLEEDING AT THE
FRACTURED ENDS DUE TO THEFRACTURED ENDS DUE TO THE
CAPPILARY BREAK OF THECAPPILARY BREAK OF THE
HAVERSIAN SYSTEM.HAVERSIAN SYSTEM.
 THERE OCCURS A CLOT FORMATIONTHERE OCCURS A CLOT FORMATION
AND RELEASE OF BLOOD CELLS ANDAND RELEASE OF BLOOD CELLS AND
PROTEINS IN THIS AREA.PROTEINS IN THIS AREA.
 ..

 THE HISTOCYTES, MAST CELLSTHE HISTOCYTES, MAST CELLS
AND THE POLYMORHS CLEARAND THE POLYMORHS CLEAR
THE DEBRIS AND BACTERIA INTHE DEBRIS AND BACTERIA IN
THE AREA, LEADING TOTHE AREA, LEADING TO
FORMATION OF GRANULATIONFORMATION OF GRANULATION
TISSUETISSUE

 • Fracture causes haemorrhage and tissue
destruction; blood clot forms (hours)
 • Proliferating fibroblasts and capillary
sprouts grow into blood clot in injured
area,forming granulation tissue, in
response to cytokines released by tissue
damage (days)

 Activated platelets release a variety of
 products [e.g. Fibronectin; platelet-derived
 growth factor (PDGF); transforming growth
 factor β (TGF-β)] which trigger the influx of
 inflammatory cells. The subsequent cytokine
 cascade brings the cells of repair (fibroblasts,
 endothelial cells and osteoblasts) into the
 fracture gap.

CELLULAR PROLIFERATIONCELLULAR PROLIFERATION
 THE GRANULATION TISSUETHE GRANULATION TISSUE
BRIDGES THE TWO BROKENBRIDGES THE TWO BROKEN
ENDS, THESE ENDS BECOMEENDS, THESE ENDS BECOME
RARIFIED AND CALCIUM IS LAIDRARIFIED AND CALCIUM IS LAID
DOWN BETWEEN THE ENDS INDOWN BETWEEN THE ENDS IN
THE GRANULATION TISSUE ASTHE GRANULATION TISSUE AS
CALLUS.CALLUS.

 • Invaded by polymorphonuclear leukocytes,
 macrophages (also responding to cytokines),
which phagocytize the debris (bloodclot, cells,
damaged matrix)
 • Granulation tissue becomes denser
 • Cartilage formed (? from primitive
mesenchymal cells or demodulation of other
 cells) (weeks)

 • Connective tissue + cartilage tissue =
callus
 • Callus temporarily binds, stabilizes bone
 • Dormant osteogenic cells of periosteum
enlarge and become osteoblasts
 • Osseous tissue deposited on outside of
bone some distance from fracture
 • Formation of new bone continues toward
fractured ends of bone.

 Connective tissue
 +
 Cartilage tissue
 =
 Callus
 Callus temporarily binds
 and stabilizes bone
 Dormant osteogenic cells of
 periosteum enlarge, become
 osteoblasts, deposit osseous
 material on outside of bone
 centripetally

 SIMILAR ACTIVITY OCCURS INSIMILAR ACTIVITY OCCURS IN
THE MEDULLARY CAVITYTHE MEDULLARY CAVITY
ALSO.THE CALLUS SO FORMEDALSO.THE CALLUS SO FORMED
IN THE MEDULLARY CAVITY ISIN THE MEDULLARY CAVITY IS
CALLED THE INTERNAL ORCALLED THE INTERNAL OR
ENDOSTEAL CALLUS,ENDOSTEAL CALLUS,

CALLUSCALLUS
 THAT FORMED OUTSIDE ISTHAT FORMED OUTSIDE IS
PAROSTEAL ORPAROSTEAL OR EXTERNALEXTERNAL
CALLUSCALLUS. THESE TWO CALLUSES. THESE TWO CALLUSES
MEET TO UNITE THE BONES.ATMEET TO UNITE THE BONES.AT
THIS STAGE THE BONE HASTHIS STAGE THE BONE HAS
UNITED BUT IS NOT STRONGUNITED BUT IS NOT STRONG
ENOUGH TO BE EXPOSED TOENOUGH TO BE EXPOSED TO
THE STRESS.THE STRESS.

 Sheath of bone is
formed
over fibrocartilaginous
 callus; osteogenic buds
invade this callus and
replace it with bony
callus; in replacement of
this callus, cartilage
undergoes calcification
and absorption

Remodeling phase
 Woven bone is remodelled into a stronger
lamellar bone by the orchestrated action of
osteoclast bone resorption and osteoblast
bone formation

REMODELLING PHASEREMODELLING PHASE
 THE SOFT CALLUS GETS HARDENED ORTHE SOFT CALLUS GETS HARDENED OR
CONSLOIDATED BY DEPOSITION OF BONECONSLOIDATED BY DEPOSITION OF BONE
SALTS, CARRIED OUT BY THESALTS, CARRIED OUT BY THE
OSTEOBLASTS.OSTEOBLASTS.
 THE MULTINUCLEATE OSTEOCLASTS COMETHE MULTINUCLEATE OSTEOCLASTS COME
IN THE ACTION AND CONTROL THE DENSITYIN THE ACTION AND CONTROL THE DENSITY
OF BONE.OF BONE.
 THE MEDULLARY CANAL IS REPRODUCEDTHE MEDULLARY CANAL IS REPRODUCED
AND THE MARROW CELLS STAR APPEARING.AND THE MARROW CELLS STAR APPEARING.
 THE BONE CELL HEALS BY FORMING NEWTHE BONE CELL HEALS BY FORMING NEW
BONE AND DOES NOT HAVE SCARBONE AND DOES NOT HAVE SCAR
FORMATIONFORMATION

Remodeling of boneRemodeling of bone
 . Multiple osteoclasts are sitting in. Multiple osteoclasts are sitting in
the Howship lacunae, resorbing onethe Howship lacunae, resorbing one
side of a bony trabecula, whileside of a bony trabecula, while
osteoblasts are depositing newosteoblasts are depositing new
bone on the other side.bone on the other side.

EFFECT OF ULTRASOUND ONEFFECT OF ULTRASOUND ON
BONE HEALINGBONE HEALING
 JW Busse et al. The effect of low-intensityJW Busse et al. The effect of low-intensity
pulsed ultrasound therapy on time topulsed ultrasound therapy on time to
fracture healing: a meta-analysis.fracture healing: a meta-analysis.
Canadian Medical Association JournalCanadian Medical Association Journal
2002 166: 437-441.2002 166: 437-441.

What is distraction osteogenesis ?
 Distraction osteogenesis is a
surgical process in which bone is
divided and fixed with a device, a
gradual lengthening of the device
by traction results in new bone
formation.

FACTORS AFFECTING BONEFACTORS AFFECTING BONE
HEALINGHEALING
 TYPE OF BONETYPE OF BONE- CANCELLOUS –- CANCELLOUS –
HEAL FASTER AS HAVEHEAL FASTER AS HAVE
ABUNDANT BLOOD SUPPLY.ABUNDANT BLOOD SUPPLY.
 TYPE OF FRACTURETYPE OF FRACTURE -SPIRAL AND-SPIRAL AND
OBLIQUE FASTER THANOBLIQUE FASTER THAN
TRANSVERSE, UPPERTRANSVERSE, UPPER
EXTREMITY FASTER , THANEXTREMITY FASTER , THAN
LOWER LIMB.LOWER LIMB.

 POSITION OF BONY ENDSPOSITION OF BONY ENDS
 EXTENT OF BLOOD SUPPLYEXTENT OF BLOOD SUPPLY
 AGE OF THE PATIENT.AGE OF THE PATIENT.

TREATMENT OF FRACTURESTREATMENT OF FRACTURES
BASIC PRINCIPLESBASIC PRINCIPLES::
 1. ACHIEVE ANATOMICAL ALIGNMENT1. ACHIEVE ANATOMICAL ALIGNMENT
 2. ASSURE CORRECT IMMOBILIZATION2. ASSURE CORRECT IMMOBILIZATION
 3. IMPROVE CIRCULATION AT3. IMPROVE CIRCULATION AT
FRACTURE SITEFRACTURE SITE
 4. REDUCE PAIN AND INFLAMMATION4. REDUCE PAIN AND INFLAMMATION
 5. PROVIDE NECESSARY5. PROVIDE NECESSARY
COMPRESSION TO CALLUSCOMPRESSION TO CALLUS
STRETCHING THE RAW CALLUS.STRETCHING THE RAW CALLUS.

BASIC METHODSBASIC METHODS
 A) REDUCTIONA) REDUCTION
 B) IMMOBILZATION- USING PLASTERB) IMMOBILZATION- USING PLASTER
OF PARISOF PARIS
 INTERNAL FIXATION- USING NAILSINTERNAL FIXATION- USING NAILS
OR PLATESOR PLATES
 EXTERNAL FIXATION – UNIPLANAR,EXTERNAL FIXATION – UNIPLANAR,
ILIZAROV.ILIZAROV.
 C) PROTECTION—SLING, SPLINTS,C) PROTECTION—SLING, SPLINTS,
BRACES.BRACES.

Biomechanics ofBiomechanics of
Fracture and FixationFracture and Fixation

Forces Acting on Long BonesForces Acting on Long Bones
 ForceForce is a vectoris a vector
(magnitude with(magnitude with
direction)direction)
 MomentMoment: Force acting: Force acting
on a bone causingon a bone causing
rotationrotation
 Moment ArmMoment Arm: lever: lever
that force acts onthat force acts on
(some distance away(some distance away
from center of rotation)from center of rotation)

Basic Forces Causing FractureBasic Forces Causing Fracture
 CompressionCompression
 TensionTension
 Transverse LoadingTransverse Loading
 TorsionTorsion

Forces On Healing FxForces On Healing Fx
 TensionTension
 CompressionCompression
 ShearShear
 (Bending)(Bending)

 CombinedCombined
bending &bending &
axial loadaxial load
 ObliqueOblique
fracturefracture
 ButterflyButterfly
fragmentfragment

Forces Acting on ConstructForces Acting on Construct
 StressStress = Force/= Force/
(Area force is acting(Area force is acting
on)on)
= (normalized force)= (normalized force)
 StrainStrain = (Change in= (Change in
Ht)/(Original Ht)Ht)/(Original Ht)
 Elastic ModulusElastic Modulus ==
Stress/StrainStress/Strain
= measure of= measure of
stiffnessstiffness

DeformationDeformation
 ElasticElastic = if load is= if load is
removed materialremoved material
returns to original shapereturns to original shape
 PlasticPlastic = residual= residual
deformation after loaddeformation after load
removedremoved
 Yield PointYield Point = load= load
when plasticwhen plastic
deformation takes placedeformation takes place
 WorkWork = Force x= Force x
(distance of bending)(distance of bending)
 ToughnessToughness = Amt of= Amt of
work req to Fx materialwork req to Fx material

Implant ShapeImplant Shape
 Moment of InertiaMoment of Inertia ::
further away materialfurther away material
is spread in an object,is spread in an object,
greater the stiffnessgreater the stiffness
 Stiffness and strengthStiffness and strength
are proportional toare proportional to
radiusradius

ViscoelasticityViscoelasticity
 Stress RelaxationStress Relaxation::
Applied force withApplied force with
constant displacementconstant displacement 
Decrease in internal forceDecrease in internal force
as resistance decreasesas resistance decreases
 resistance decreases asresistance decreases as
fluid is forced from syringefluid is forced from syringe
 Trabecular BoneTrabecular Bone ::
Trabecular structure actsTrabecular structure acts
as elastic component,as elastic component,
Interstitial fluid thru porousInterstitial fluid thru porous
matrix is viscousmatrix is viscous
componentcomponent
 Under higher loading rateUnder higher loading rate
there is resistance to flowthere is resistance to flow
thus increased internalthus increased internal
pressure thus increasedpressure thus increased
stiffness of bonestiffness of bone

ViscoelasticityViscoelasticity
 Increased resistance withIncreased resistance with
increased loading rateincreased loading rate
 CreepCreep = under constant= under constant
load soft tissue willload soft tissue will
continue tocontinue to graduallygradually
deformdeform
 If compressive force isIf compressive force is
applied slowly, syringeapplied slowly, syringe
offers little resistanceoffers little resistance
 Increased rate of force,Increased rate of force,
increased resistance toincreased resistance to
rate of motion of syringerate of motion of syringe

FatigueFatigue
 Cyclic LoadsCyclic Loads below failure levelbelow failure level 
progressive cracksprogressive cracks  failurefailure
 Stress ConcentratorStress Concentrator = radical change in= radical change in
shapeshape
 Galvanic CorosionGalvanic Corosion = Flow of electrons from= Flow of electrons from
(-) to (+) in 2 dissimilar materials in conductive(-) to (+) in 2 dissimilar materials in conductive
fluidfluid
 FrettingFretting = rubbing of 2 surfaces together= rubbing of 2 surfaces together
(removing oxidative layer)(removing oxidative layer)
 Crevice CorrosionCrevice Corrosion = impurities in material= impurities in material

Crevice Stress
Fretting Galvanic

Biomechanics Intact/HealingBiomechanics Intact/Healing
BoneBone
 Hierarchical structureHierarchical structure
 Collagen embedded withCollagen embedded with
apatiteapatite
 Decreased modulus withDecreased modulus with
decreaseddecreased
apatite:collagen ratioapatite:collagen ratio
 Fibrils organized to resistFibrils organized to resist
forceforce
 Fibers organized intoFibers organized into
lamellaelamellae
 Concentric LemellaeConcentric Lemellae
make an Osteonmake an Osteon

Strength/StiffnessStrength/Stiffness
 Strength proportional toStrength proportional to
densitydensity
 Modulus proportional toModulus proportional to
densitydensity
 AgeAge: increased modulus,: increased modulus,
bending strength frombending strength from
child to adult, thenchild to adult, then
decreasedecrease
 Holes/defectsHoles/defects weakenweaken
bone (round better thanbone (round better than
square)square)
 Strength proportional toStrength proportional to
diameterdiameter

Biomechanics of Bone FxBiomechanics of Bone Fx
 Weakest inWeakest in
Tension, StrongestTension, Strongest
in Compressionin Compression
 PurePure BendingBending 
TransverseTransverse FxFx
 TorsionTorsion  SpiralSpiral
FxFx
 ShearShear  ObliqueOblique
FxFx
 ButterflyButterfly due todue to
Bend + ShearBend + Shear

 Smaller cross section ofSmaller cross section of
bone fails 1bone fails 1stst
(distal 1/3(distal 1/3
of tibia)of tibia)
 OsteoperosisOsteoperosis
 decreased density ofdecreased density of
trebecular bonetrebecular bone
 decreased endostealdecreased endosteal
thickness of cortical bonethickness of cortical bone

Bone HealingBone Healing
 DirectDirect
 Primary bone healingPrimary bone healing
 Cutting conesCutting cones
 Seen with absolute stabilitySeen with absolute stability
 IndirectIndirect
 Secondary bone healingSecondary bone healing
 Callus formation; resorption at fx site;Callus formation; resorption at fx site;
 Seen with relative stabilitySeen with relative stability

Indirect Stages:Indirect Stages:
 InflammationInflammation
 1-7 days1-7 days
 Soft callusSoft callus
 3 weeks3 weeks
 Hard callusHard callus
 3 – 4 months3 – 4 months
 RemodelingRemodeling
 months => yearsmonths => years

Relative StabilityRelative Stability
 MotionMotion betweenbetween fracture fragmentsfracture fragments that isthat is
compatiblecompatible withwith fracture healing.fracture healing.
 Motion is below theMotion is below the critical strain levelcritical strain level ofof
tissue repair.tissue repair.
 PromotesPromotes indirectindirect bone healing!bone healing!
 Examples:Examples:
 IM nailsIM nails
 Bridge plateBridge plate
 External FixatorExternal Fixator

Absolute StabilityAbsolute Stability
 CompressionCompression of twoof two anatomicallyanatomically
reducedreduced fracture fragmentsfracture fragments..
 No displacementNo displacement of the fractureof the fracture
underunder functional load.functional load.
 PromotesPromotes directdirect bone healing!bone healing!
 Examples:Examples:
 Lag screwLag screw
 PlatePlate => compression, buttress,=> compression, buttress,
neutralizationneutralization
 Tension bandTension band

 Preload > external load => absolutePreload > external load => absolute
stabilitystability
 External load > preload => relative stabilityExternal load > preload => relative stability
 External load >> preload => frankExternal load >> preload => frank
instabilityinstability

Biomechanics of Implants:Biomechanics of Implants:
Avoiding ProblemsAvoiding Problems
 Cerclage Wire: strength proportional toCerclage Wire: strength proportional to
diameterdiameter
 Solid wire sensitive to scratch/notch (cableSolid wire sensitive to scratch/notch (cable
better)better)
 Optimal no. of turns 4-8 when twistedOptimal no. of turns 4-8 when twisted

Screw fixationScrew fixation
 Rotary forcesRotary forces  compression betweencompression between
objects (inclined plane on spiral pullsobjects (inclined plane on spiral pulls
object toward head)object toward head)
 Four part construction:Four part construction: head, shaft,head, shaft,
thread,thread, tiptip
 Thread defined byThread defined by root diameter,root diameter,
threadthread diameter, pitchdiameter, pitch

ScrewsScrews
 Larger coreLarger core diameterdiameter
hashas higher resistancehigher resistance
to fatigue & shearto fatigue & shear
failurefailure
 4th power of the diameter4th power of the diameter
 Pullout strengthPullout strength
(maximum force screw(maximum force screw
can support along its axis)can support along its axis)
 outer diameter, length ofouter diameter, length of
engagement, shearengagement, shear
strength/density of bonestrength/density of bone

ScrewsScrews
 TappingTapping
 increase compressiveincrease compressive
forces, decrease interfaceforces, decrease interface
frictionfriction
 Cyclic LoadingCyclic Loading : If: If
plate is not tight enoughplate is not tight enough
to boneto bone
 Force transferred to longForce transferred to long
axis of screwaxis of screw
 Stress corrosion of plateStress corrosion of plate
rubbingrubbing

Plates & BendingPlates & Bending
failurefailure
 Leaving gap opposite to theLeaving gap opposite to the
plate makes it a fulcrumplate makes it a fulcrum
 increased stress at holesincreased stress at holes
 avoid holes over fractureavoid holes over fracture
sitessites
 greater the span betweengreater the span between
screwsscrews
 less stiffless stiff
 more bendingmore bending

Femoral NailFemoral Nail
 Contact ForcesContact Forces
expand femur (hoopexpand femur (hoop
stresses) may causestresses) may cause
it to split if too largeit to split if too large
 Starting hole: tooStarting hole: too
medial, too anteriormedial, too anterior
 Initial curve of IM rod,Initial curve of IM rod,
rod stiffnessrod stiffness

Femoral NailFemoral Nail
 Distal Fx:Distal Fx:
 Longer moment arm of externalLonger moment arm of external
force thus greater bendingforce thus greater bending
moment in rodmoment in rod
 Greatest area of stress in rod (FxGreatest area of stress in rod (Fx
site) is near screw holes (stresssite) is near screw holes (stress
riser)riser)
 Locking screw supported only byLocking screw supported only by
corticescortices
 Stiffness & strength to bendStiffness & strength to bend
decrease with lengthdecrease with length
 Possible to nick border of rodPossible to nick border of rod
hole w/ screwhole w/ screw  accentuateaccentuate
fatiguefatigue

INTERLOCKING NAILINTERLOCKING NAIL
 Controls torsion and axial loadsControls torsion and axial loads
 AdvantagesAdvantages
 Axial and rotational stabilityAxial and rotational stability
 Angular stabilityAngular stability
 DisadvantagesDisadvantages
 Time and radiation exposureTime and radiation exposure
 Stress riser in nailStress riser in nail
 Location of screwsLocation of screws
 Screws closer to the end of the nail expand the zoneScrews closer to the end of the nail expand the zone
of fxs that can be fixed at the expense of constructof fxs that can be fixed at the expense of construct
stabilitystability

Intramedullary NailsIntramedullary Nails
 ““Internal Splint”, Load SharingInternal Splint”, Load Sharing
 Nail itself should resist bending andNail itself should resist bending and
torsiontorsion
 The bone should resist axial loadingThe bone should resist axial loading
 Strength => wall thickness, diameter, andStrength => wall thickness, diameter, and
materialmaterial
 stiffness => 4th power of the diameterstiffness => 4th power of the diameter
 Type of fracture –transverse, oblique, orType of fracture –transverse, oblique, or
complex determines some stabilitycomplex determines some stability

 Working lengthWorking length is area that spansis area that spans
fracture between points of fixation.fracture between points of fixation.
 In bending,In bending, stiffnessstiffness inverselyinversely
proportional to square of lengthproportional to square of length
 Torsional rigidityTorsional rigidity is inverselyis inversely
proportional to lengthproportional to length

 Gripping strength is resistance to slippingGripping strength is resistance to slipping
at bone-implant interface. Increased byat bone-implant interface. Increased by
increasing cortical contact.increasing cortical contact.
 Nail can twist or slip with torsional loadingNail can twist or slip with torsional loading
which allows angulationwhich allows angulation

interlockinginterlocking
 Dynamic fixationDynamic fixation controls bending andcontrols bending and
rotation, but allows axial loadingrotation, but allows axial loading
 Static lockingStatic locking controls bending, rotation,controls bending, rotation,
and axial loadingand axial loading

interlockinginterlocking

 femoral splittingfemoral splitting
 starting pointstarting point
 length of proximallength of proximal
fragmentfragment
 initial curvatureinitial curvature
 stiffnessstiffness

Ex-FixEx-Fix
 Self-tapping pinsSelf-tapping pins  local heatlocal heat
 thermal necrosis &thermal necrosis &
microcracking (thusmicrocracking (thus
corrosion/fatigue)corrosion/fatigue)
 Pin MicromotionPin Micromotion  bonebone
resorption at interfaceresorption at interface
 Undersize hole 0.1 mmUndersize hole 0.1 mm  decrdecr
micromotionmicromotion
 Undersize >0.3 mmUndersize >0.3 mm  incrincr
microcrackingmicrocracking

Ex-FixEx-Fix
 Deformation of Pin or Side BarDeformation of Pin or Side Bar
 Stiffness & Strength proportional to diameterStiffness & Strength proportional to diameter44
 Stiffness & Strength inversely proportional to lenghtStiffness & Strength inversely proportional to lenght33
 To increase strength:To increase strength:
 Decrease sidebar to bone distanceDecrease sidebar to bone distance
 Increase pin diameterIncrease pin diameter
 Put pins closer to fracturePut pins closer to fracture
 Increase # of sidebarsIncrease # of sidebars
 Bury pin thread completely within cortexBury pin thread completely within cortex
 Add Sidebar at 90 degree plane also resist torsionAdd Sidebar at 90 degree plane also resist torsion

Biomechanics: Metals andBiomechanics: Metals and
MethylmethacrylateMethylmethacrylate

IntroductionIntroduction
 Metallurgy= the art and science of usingMetallurgy= the art and science of using
metalsmetals
 Biomaterial requirements:Biomaterial requirements:
 BiocompatibleBiocompatible
 Resist corrosion/degradationResist corrosion/degradation
 Possess adequate mechanical propertiesPossess adequate mechanical properties
 Especially important for load bearing devicesEspecially important for load bearing devices
 Reproducible fabricationReproducible fabrication
 Reasonable costReasonable cost

Biomechanics ReviewBiomechanics Review
 StressStress = distribution of internal forces (= distribution of internal forces (stress =stress =
load / area)load / area)
 StrainStrain == change in linear dimensions of a bodychange in linear dimensions of a body
resulting from the application of a force or loadresulting from the application of a force or load
 ToughnessToughness == ability of a metal to absorb energyability of a metal to absorb energy
by bending without breakage (area under theby bending without breakage (area under the
stress-strain curve )stress-strain curve )
 CreepCreep == amount of deformation that a materialamount of deformation that a material
undergoes with time as it is subjected a constantundergoes with time as it is subjected a constant
loadload

 Elastic modulusElastic modulus = material’s stiffness,= material’s stiffness,
stress/strain, slope of stress-strain curvestress/strain, slope of stress-strain curve
 Plastic deformationPlastic deformation = permanent change= permanent change
in shape after load is removedin shape after load is removed
 Yield stressYield stress = stress at transition between= stress at transition between
elastic & plastic on stress-strain curveelastic & plastic on stress-strain curve
 Ultimate stressUltimate stress = maximum stress prior to= maximum stress prior to
rupturerupture

Stress-Strain CurveStress-Strain Curve

 BrittleBrittle = sustains little or no permanent= sustains little or no permanent
deformation prior to failuredeformation prior to failure
 DuctileDuctile = can sustain large amounts of= can sustain large amounts of
permanent deformation prior to failurepermanent deformation prior to failure
 ViscoelasticityViscoelasticity == stress/strain behavior that isstress/strain behavior that is
time-rate dependenttime-rate dependent (eg.(eg. elongation of ligamentelongation of ligament
being more likely to occur with slower loadingbeing more likely to occur with slower loading
conditionsconditions ))
 FatigueFatigue = structural failure from repetitive= structural failure from repetitive
stresses below ultimate stressstresses below ultimate stress

Orthopaedic MetalsOrthopaedic Metals
 Alloy metals = mixtures of metallic andAlloy metals = mixtures of metallic and
non-metallic elementsnon-metallic elements
 3 common alloys:3 common alloys:
 Stainless steelStainless steel
 Cobalt chromiumCobalt chromium
 TitaniumTitanium
 New metal:New metal:
 Porous Trabecular Tantalum MetalPorous Trabecular Tantalum Metal

MetalsMetals
 Metallic bonds:Metallic bonds:
 CrystallineCrystalline
 Densely packed atomic nuclei in ordered,Densely packed atomic nuclei in ordered,
repeating 3D patternrepeating 3D pattern
 Valence electrons flow easily betweenValence electrons flow easily between
adjoining atomsadjoining atoms
 Accounts for high electrical and thermalAccounts for high electrical and thermal
conductivity, chemical reactivityconductivity, chemical reactivity

MetalsMetals
 3 basic atomic3 basic atomic
configurationsconfigurations
 Atoms fill 70-75% ofAtoms fill 70-75% of
possible volumepossible volume

MetalsMetals
 Tightness of a metal’s crystalline packingTightness of a metal’s crystalline packing
defines grain sizedefines grain size
 Smaller grain size = more homogeneous andSmaller grain size = more homogeneous and
isotropic= greater strengthisotropic= greater strength
 Larger grain sizes = insufficient fatigueLarger grain sizes = insufficient fatigue
strength and clinical failurestrength and clinical failure

Stainless SteelStainless Steel
 316L, grade 2316L, grade 2
 ““L” = low carbon concentration (0.03 wt%)L” = low carbon concentration (0.03 wt%)
 Alloy of iron and carbonAlloy of iron and carbon
 Cr, Ni, Mo, Mn, P, S, SiCr, Ni, Mo, Mn, P, S, Si
 Passivation:Passivation:
 Chromium forms oxide when exposed to environmentChromium forms oxide when exposed to environment
= corrosion resistant= corrosion resistant
 Steel receives nitric acid bath creating passive oxideSteel receives nitric acid bath creating passive oxide
layer = “stainless”layer = “stainless”
 1,000 to 1,000,000 times more corrosion resistant1,000 to 1,000,000 times more corrosion resistant

 Cold-workingCold-working
 Cold working afterCold working after
solidification cansolidification can
reduce grain sizereduce grain size
 Most orthopedicMost orthopedic
steel is cold-steel is cold-
worked 30%worked 30%
 Cold-forged= evenCold-forged= even
better strengthbetter strength

 DisadvantageDisadvantage
 Susceptible to crevice and stress corrosionSusceptible to crevice and stress corrosion
 Decreased pH, increased oxidation, andDecreased pH, increased oxidation, and
accelerated corrosion occurs in crevices inaccelerated corrosion occurs in crevices in
the metal, eg. Underside of screw head on athe metal, eg. Underside of screw head on a
plateplate
 Stress corrosion crackingStress corrosion cracking
 Corrosion accelerates cracking, leading to failureCorrosion accelerates cracking, leading to failure
under lower than normal stress levelsunder lower than normal stress levels

 Main use in fractures and spinal fixationMain use in fractures and spinal fixation
 Require strength only until healing is completeRequire strength only until healing is complete
 Charnley stemCharnley stem

Cobalt-chromeCobalt-chrome
 Casted, forged, or coldCasted, forged, or cold
workedworked
 Chromium for corrosionChromium for corrosion
resistanceresistance
 Easy to makeEasy to make
 Widely used:Widely used:
 Any metal component ofAny metal component of
many total jointsmany total joints
 Fracture fixationFracture fixation
 F75 casted alloy for porousF75 casted alloy for porous
coatingcoating

 Casted alloysCasted alloys
 Difficult quality controlDifficult quality control
 Solidifying too slowly allows grains to grow too large=Solidifying too slowly allows grains to grow too large=
loses strengthloses strength
 Solidifying too fast traps gasses in microstructure=Solidifying too fast traps gasses in microstructure=
stress risersstress risers
 Powder metallurgyPowder metallurgy
 Fine powder of alloy compacted into net shapeFine powder of alloy compacted into net shape
 Pressure forged and heated into final shapePressure forged and heated into final shape
 Smaller grainsSmaller grains

 Hot forging and cold working greatlyHot forging and cold working greatly
improve strengthimprove strength
 Among the strongest orthopaedic implantAmong the strongest orthopaedic implant
alloys availablealloys available
 Good for articulations, low wear generatesGood for articulations, low wear generates
less metal debrisless metal debris

Cancer Risk After Metal on Metal andCancer Risk After Metal on Metal and
Polyethylene on Metal Total HipPolyethylene on Metal Total Hip
ArthroplastyArthroplasty
 579 Metal on metal (CoCr) from 1967 to579 Metal on metal (CoCr) from 1967 to
19731973
 15 yrs follow-up, 9,000 person years15 yrs follow-up, 9,000 person years
 113 cancers seen, 118 expected113 cancers seen, 118 expected
 1585 Metal on poly from 1973 to 19851585 Metal on poly from 1973 to 1985
 12 yrs follow-up, 20,000 person years12 yrs follow-up, 20,000 person years
 212 cancers seen, 278 expected212 cancers seen, 278 expected
 Compared to National Cancer RegistryCompared to National Cancer Registry

Cancer Risk After Metal on Metal andCancer Risk After Metal on Metal and
Polyethylene on Metal Total HipPolyethylene on Metal Total Hip
ArthroplastyArthroplasty
 Metal on poly wear 100x more than metalMetal on poly wear 100x more than metal
on metalon metal
 Hundreds of billions of submicronHundreds of billions of submicron
polyethylene particles are annually releasedpolyethylene particles are annually released
from the polyethylene cupfrom the polyethylene cup
 Metal on metal wear is less than 10 mm3 perMetal on metal wear is less than 10 mm3 per
yearyear

ConclusionConclusion
 No statistically significant increases in cancerNo statistically significant increases in cancer
risk for either grouprisk for either group
 The incidence of the other forms ofThe incidence of the other forms of
cancers did not differ significantly fromcancers did not differ significantly from
those in the general population.those in the general population.
 The observed variation in the incidence ofThe observed variation in the incidence of
different cancers among patients who had totaldifferent cancers among patients who had total
hip arthroplasty compared with the generalhip arthroplasty compared with the general
population suggests that factors other than totalpopulation suggests that factors other than total
hip arthroplasty play a major role in cancer.hip arthroplasty play a major role in cancer.

TitaniumTitanium
 ExcellentExcellent
biocompatabilitybiocompatability
 Very resistant toVery resistant to
corrosioncorrosion
 Titanium oxide layerTitanium oxide layer
exceeds protection ofexceeds protection of
steel and cobalt (selfsteel and cobalt (self
passivation)passivation)
 Oxide surface wellOxide surface well
tolerated by bone,tolerated by bone,
integrate wellintegrate well
 Primary alloyPrimary alloy
elements: aluminum,elements: aluminum,
vanadiumvanadium

TitaniumTitanium
 F-136 alloy most common in orthopaedicsF-136 alloy most common in orthopaedics
 High strength-to-weight ratioHigh strength-to-weight ratio
 Mechanical properties:Mechanical properties:
 Elastic modulus= ½ that of steel and cobalt,Elastic modulus= ½ that of steel and cobalt,
 lowers structural stiffness without changing shapelowers structural stiffness without changing shape
 less stress shielding, load shares with boneless stress shielding, load shares with bone
 Widely used:Widely used:
 Fracture fixation, IM rods, total joint stemsFracture fixation, IM rods, total joint stems

TitaniumTitanium
 DisadvantagesDisadvantages
 Notch sensitiveNotch sensitive
 Scratches easily, these stress risers reduce fatigueScratches easily, these stress risers reduce fatigue
lifelife
 Difficult to porous coatDifficult to porous coat
 Sintering process creates stress risersSintering process creates stress risers
 Low hardnessLow hardness
 Soft, not wear resistant, not good for articulationsSoft, not wear resistant, not good for articulations
 High levels of Ti/Al found in joint fluid and tissuesHigh levels of Ti/Al found in joint fluid and tissues
when used as femoral headwhen used as femoral head

TitaniumTitanium
 Bottom Line: excellent resistance toBottom Line: excellent resistance to
fatigue, but is extremely susceptible tofatigue, but is extremely susceptible to
wear and is highly notch sensitivewear and is highly notch sensitive
 Commonly used for plates and stems, butCommonly used for plates and stems, but
not good for bearing surfacenot good for bearing surface

Trabecular Tantalum MetalTrabecular Tantalum Metal
 TantalumTantalum
 The most biocompatible, corrosion resistant element used inThe most biocompatible, corrosion resistant element used in
medical devicesmedical devices
 Pacemakers, wire, foil, mesh for nerve repair, femoralPacemakers, wire, foil, mesh for nerve repair, femoral
endoprosthesesendoprostheses

Tantalum vs. Trabecular BoneTantalum vs. Trabecular Bone
Similar stiffness andSimilar stiffness and
porosityporosity

Trabecular MetalTrabecular Metal
distinguished fromdistinguished from
current porous materialscurrent porous materials
by itsby its
 uniformity anduniformity and
structural continuitystructural continuity
– low stiffness
– Toughness
– resistance to fatigue failure
– greater volumetric porosity 80% vs.
20-30%

Trabecular Metal -- AdvantagesTrabecular Metal -- Advantages
 Excellent bone andExcellent bone and
tissue ingrowthtissue ingrowth
 Implants with lessImplants with less
rigidityrigidity
 Better frictionalBetter frictional
characteristicscharacteristics
 Direct polyethyleneDirect polyethylene
intrusion into theintrusion into the
metal substrate tometal substrate to
eliminate backsideeliminate backside
wearwear

Trabecular Metal --Trabecular Metal --
DisadvantagesDisadvantages
 No known trackNo known track
record in total jointsrecord in total joints
 Bony in growth mayBony in growth may
make revisionsmake revisions
extremely difficultextremely difficult

Trabecular Metal – OrthopaedicTrabecular Metal – Orthopaedic
applicationsapplications
 primary and revision hip and kneeprimary and revision hip and knee
implantsimplants
 spinal interbody fusion devicesspinal interbody fusion devices
 soft tissue attachment devicessoft tissue attachment devices
 trauma void filling structural applicationstrauma void filling structural applications

CeramicsCeramics
 Very HardVery Hard
 Excellent bearing propertiesExcellent bearing properties
 VERY low frictionVERY low friction
 Very low particle wearVery low particle wear
 Risk of catastrophic fractureRisk of catastrophic fracture
 Decreased bony ingrowth in acetabulumDecreased bony ingrowth in acetabulum

Press-Fit Metal-Backed AluminaPress-Fit Metal-Backed Alumina
Sockets: A Minimum 5-Year FollowupSockets: A Minimum 5-Year Followup
StudyStudy
 234 consecutive alumina-on-alumina hip234 consecutive alumina-on-alumina hip
replacements using a press-fit metal-backedreplacements using a press-fit metal-backed
socketsocket
 201 primary procedures and 33 revision procedures,201 primary procedures and 33 revision procedures,
62 years (range, 21–83 years)62 years (range, 21–83 years)
 11 hips underwent revision11 hips underwent revision
 recurrent dislocation (one hip)recurrent dislocation (one hip)
 deep infection (two hips)deep infection (two hips)
 fracture of alumina femoral head (one hip)fracture of alumina femoral head (one hip)
 persistent hip pain (one hip)persistent hip pain (one hip)
 aseptic loosening (six hips)aseptic loosening (six hips)
 The survival rate after 9 years was 93.4%The survival rate after 9 years was 93.4%
 Results were excellent in 148 hips (80.5%), very goodResults were excellent in 148 hips (80.5%), very good
in 31 hips (17%), good in two hips (1%), and fair inin 31 hips (17%), good in two hips (1%), and fair in
three hips (1.5%).three hips (1.5%).

Press-Fit Metal-Backed AluminaPress-Fit Metal-Backed Alumina
Sockets: A Minimum 5-Year FollowupSockets: A Minimum 5-Year Followup
StudyStudy
 Radiologic data were documented for 134Radiologic data were documented for 134
patients (143 hips).patients (143 hips).
 Three sockets (2%) had a complete andThree sockets (2%) had a complete and
nonprogressive radiolucent line less than 1-mmnonprogressive radiolucent line less than 1-mm
thickthick
 one stem (0.7%) had lucencies involving five zonesone stem (0.7%) had lucencies involving five zones
 two stems (1.4%) had isolated femoral osteolysistwo stems (1.4%) had isolated femoral osteolysis
 Neither component migration nor acetabularNeither component migration nor acetabular
osteolysis were detected.osteolysis were detected.
 A press-fit metal-backed socket may offer aA press-fit metal-backed socket may offer a
good solution for alumina socket fixationgood solution for alumina socket fixation
when combined with a careful surgicalwhen combined with a careful surgical
technique of implantation.technique of implantation.

PMMAPMMA
 PolymerPolymer
 Large molecule made from combo of smallerLarge molecule made from combo of smaller
moleculesmolecules
 Introduced by Charnley in 1970’sIntroduced by Charnley in 1970’s
 2 parts:2 parts:
 Liquid methylmethacrylate monomerLiquid methylmethacrylate monomer
 Hydroquinone (polymerization inhibitor)Hydroquinone (polymerization inhibitor)
 PMMA powderPMMA powder
 Dibenzoyl peroxide (initiator)Dibenzoyl peroxide (initiator)
 Radiopaque BaSO4 or ZrO2Radiopaque BaSO4 or ZrO2

PMMAPMMA
 2 viscosity types2 viscosity types
 DoughyDoughy
 High viscosity from mixingHigh viscosity from mixing
 InjectableInjectable
 Delayed hardening, allows vacuum/centrifuge andDelayed hardening, allows vacuum/centrifuge and
cement gun deliverycement gun delivery

PMMAPMMA
 Exothermic polymerizationExothermic polymerization
 130cal/g MMA polymer130cal/g MMA polymer
 Heat rise depends on cement thickness,Heat rise depends on cement thickness,
amount of cement, heat transfer to tissueamount of cement, heat transfer to tissue
 Protein denature @ 56degC, bone necrosisProtein denature @ 56degC, bone necrosis
@ 47degC@ 47degC
 Actual in vitro temp around 40degCActual in vitro temp around 40degC
 Thermal necrosis not a problemThermal necrosis not a problem

PMMAPMMA
 Modulus of Elasticity less than the metals,Modulus of Elasticity less than the metals,
less than cortical bone, but greater thanless than cortical bone, but greater than
cancellous bonecancellous bone
 Reaches ultimate strength within 24 hoursReaches ultimate strength within 24 hours
 Strong in compression, weak in tensionStrong in compression, weak in tension
and shearand shear

PMMA:PMMA:
Cement TechniqueCement Technique
 First GenerationFirst Generation
 Hand mix with spatulaHand mix with spatula
 Leave cancellous boneLeave cancellous bone
 Irrigate and suction canalIrrigate and suction canal
 Manual insertion at dough stageManual insertion at dough stage
 Manual centralization of stemManual centralization of stem

PMMA:PMMA:
 Second generationSecond generation
 Hand mixHand mix
 Remove cancellous boneRemove cancellous bone
 Distal cement restrictorDistal cement restrictor
 Brush, pulse lavage canalBrush, pulse lavage canal
 Pack and dry canalPack and dry canal
 Cement gunCement gun
 Manual centralization of stemManual centralization of stem
 Improved stem shapesImproved stem shapes

PMMA:PMMA:
 Third GenerationThird Generation
 Vacuum or centrifuge mixingVacuum or centrifuge mixing
 Remove cancellous boneRemove cancellous bone
 Distal cement restrictorDistal cement restrictor
 Brush, pulse lavage canalBrush, pulse lavage canal
 Pack with adrenaline sponge, then dryPack with adrenaline sponge, then dry
spongesponge
 Cement gun & pressurizationCement gun & pressurization
 Distal and proximal centralizersDistal and proximal centralizers
 Surface texture/coating of stemSurface texture/coating of stem

PMMA:PMMA:
 Centrifugation or vacuumCentrifugation or vacuum
 reduces porosity of cement by 50% vs. handreduces porosity of cement by 50% vs. hand
mixmix
 Increases tensile strength 44% vs. hand mixIncreases tensile strength 44% vs. hand mix
 Reduction in voids increases strength andReduction in voids increases strength and
decreases crackingdecreases cracking
 AntibioticsAntibiotics
 Several reports of addition of Abx weakeningSeveral reports of addition of Abx weakening
cementcement
 In general, therapeutic levels of Abx won’tIn general, therapeutic levels of Abx won’t
change measurable propertieschange measurable properties

100 Cemented Versus 100100 Cemented Versus 100
Noncemented Stems With ComparisonNoncemented Stems With Comparison
of 25 Matched Pairsof 25 Matched Pairs
 Two series of 100 consecutive primaryTwo series of 100 consecutive primary
total hip arthroplasties, (all 28 mm heads)total hip arthroplasties, (all 28 mm heads)
 One cemented and two noncementedOne cemented and two noncemented
stems underwent revision for asepticstems underwent revision for aseptic
looseningloosening
 Of unrevised hips, outcome dataOf unrevised hips, outcome data
statistically favored cemented, rather thanstatistically favored cemented, rather than
noncemented, stems.noncemented, stems.

 The data for cemented and noncementedThe data for cemented and noncemented
stems, respectively, werestems, respectively, were
 excellent to good result in 97% versus 88%;excellent to good result in 97% versus 88%;
 thigh pain in 3% versus 40%;thigh pain in 3% versus 40%;
 subsidence in 0% versus 22%;subsidence in 0% versus 22%;
 and endosteal cavitation in 6% versus 12%.and endosteal cavitation in 6% versus 12%.

 For patients with 25 unrevised matched pairs,For patients with 25 unrevised matched pairs,
selected by gender, age, diagnosis, and weight,selected by gender, age, diagnosis, and weight,
outcome data also statistically favored cemented overoutcome data also statistically favored cemented over
noncemented stemsnoncemented stems
 an excellent or good result in 25 versus 20 hips;an excellent or good result in 25 versus 20 hips;
 thigh pain in two versus eight hips;thigh pain in two versus eight hips;
 and subsidence in none versus six hips.and subsidence in none versus six hips.
 Midterm followup data for these concurrent total hipMidterm followup data for these concurrent total hip
arthroplasty series of a mid1980s design revealedarthroplasty series of a mid1980s design revealed
prevalence of mechanical failure of 1% for cementedprevalence of mechanical failure of 1% for cemented
stems and 4% for noncemented stems.stems and 4% for noncemented stems.

PROSTALACPROSTALAC
 A prospective study of 49 patients, 2-stageA prospective study of 49 patients, 2-stage
exchange arthroplasty for infected THA and TKAexchange arthroplasty for infected THA and TKA
using antibiotic-loaded acrylic cementusing antibiotic-loaded acrylic cement
((PROSTALACPROSTALAC) system with a variety of doses) system with a variety of doses
of tobramycin and vancomycin was performed.of tobramycin and vancomycin was performed.
 The intra-articular concentrations of tobramycinThe intra-articular concentrations of tobramycin
and vancomycin were measured at the time ofand vancomycin were measured at the time of
removal of theremoval of the PROSTALACPROSTALAC temporary spacertemporary spacer
and reimplantation of a definitive jointand reimplantation of a definitive joint
arthroplasty prosthesis, at a mean 118 daysarthroplasty prosthesis, at a mean 118 days
following initial implantation.following initial implantation.

TobramycinTobramycin
 The 95% confidence interval of the intra-The 95% confidence interval of the intra-
articular concentration of tobramycinarticular concentration of tobramycin
(4.35-123.88 mg/L) was entirely above the(4.35-123.88 mg/L) was entirely above the
breakpoint sensitivity limit for sensitivebreakpoint sensitivity limit for sensitive
organisms when at least 3.6 g oforganisms when at least 3.6 g of
tobramycin was used per package oftobramycin was used per package of
bone-cementbone-cement
 Entirely below it when at most 2.4 g wasEntirely below it when at most 2.4 g was
used.used.

VancomycinVancomycin
 Vancomycin elution was not as goodVancomycin elution was not as good
 However, detectable levels were stillHowever, detectable levels were still
present in most patients. There was apresent in most patients. There was a
statistically significant increase in thestatistically significant increase in the
elution of vancomycin when the dose ofelution of vancomycin when the dose of
tobramycin was increased from at mosttobramycin was increased from at most
2.4 g to at least 3.6 g.2.4 g to at least 3.6 g.
 The dose of vancomycin in the cement didThe dose of vancomycin in the cement did
not influence the elution of eithernot influence the elution of either
tobramycin or vancomycin.tobramycin or vancomycin.

ConclusionConclusion
 On the basis of these results, the use of atOn the basis of these results, the use of at
least 3.6 g of tobramycin and 1 g ofleast 3.6 g of tobramycin and 1 g of
vancomycin per package of bone-cementvancomycin per package of bone-cement
is recommended when antibiotic-loadedis recommended when antibiotic-loaded
cement spacers are used in 2-stagecement spacers are used in 2-stage
exchange arthroplasty for infected total hipexchange arthroplasty for infected total hip
and knee arthroplasties.and knee arthroplasties.

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