FRACTURES AND FRACTURES AND FRACTURE HEALINGFRACTURE HEALING

DR.JAYANT SHARMADR.JAYANT SHARMAM.S., D.N.B., M.N.A.M.S.M.S., D.N.B., M.N.A.M.S.

CONSULTANT ORTHOPAEDICS AND SPORTS CONSULTANT ORTHOPAEDICS AND SPORTS MEDICINEMEDICINE

ARIHANT HOSPITAL ARIHANT HOSPITAL INDOREINDORE

BONESBONES Bones are surprisingly light, Bones are surprisingly light,

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

PeriosteumPeriosteum

The Periosteum is composed of an inner The Periosteum is composed of an inner cambium layer that is immediately cambium layer that is immediately adjacent to the bone surface and an outer adjacent to the bone surface and an outer dense fibrous layer.dense fibrous layer.

Cambium layer consists of osteoprogenitor consists of osteoprogenitor cells.cells.

These are flat and spindle shaped and are These are flat and spindle shaped and are capable of differentiating into osteoblasts capable of differentiating into osteoblasts and forming bones in response to various and forming bones in response to various stimulationsstimulations

The periosteum is thick and loosely The periosteum is thick and loosely attached to the cortex in children, but attached to the cortex in children, but it is thinner and more adherent in it is thinner and more adherent in adults. adults.

The periosteum carries a dense The periosteum carries a dense network of blood, lymphatic vessels, network of blood, lymphatic vessels, and predominantly sensory nerves for and predominantly sensory nerves for maintenance of the bone structuremaintenance of the bone structure

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

Different patterns of periosteal stimulation Different patterns of periosteal stimulation result in different patterns of periosteal bone result in different patterns of periosteal bone formation. formation.

Continual insultContinual insult results in streams of periosteal results in streams of periosteal bone that are perpendicular to the bone bone that are perpendicular to the bone surface, resulting in a hair-on-end appearance surface, resulting in a hair-on-end appearance on radiographs. on radiographs.

Intermittent periosteal stimulationIntermittent periosteal stimulation results in results in multiple partially separated streams of multiple partially separated streams of periosteal bone, parallel to the bone surface, periosteal bone, parallel to the bone surface, giving an onionskin appearance on giving an onionskin appearance on radiographsradiographs

Periosteum

A very importantsource of bone formingcells

EndosteumEndosteum

The endosteum is composed of The endosteum is composed of osteoprogenitor cells and only a small osteoprogenitor cells and only a small amount of connective tissue.amount of connective tissue.

Covering the surface of bone Covering the surface of bone trabeculae and the medullary surface of trabeculae and the medullary surface of cortical bone and haversian canals. cortical bone and haversian canals. 

The endosteum serves as one of the The endosteum serves as one of the functional surfaces for bone remodeling functional surfaces for bone remodeling

PeriosteumEndosteumBone marrowOther sites

TYPES OF BONE TISSUETYPES OF BONE TISSUE Bone tissue can be classified in Bone tissue can be classified in

several ways, includingseveral ways, including texture, texture, matrix arrangement, matrix arrangement, maturity, and maturity, 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 bone is ivorylike and dense in texture without cavities. It is the shell of many bones and surrounds cavities. It is the shell of many bones and surrounds the trabecular bone in the center. Compact bone the trabecular bone in the center. Compact bone consists mainly of haversian systems or consists mainly 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 spongelike Sponge bone is so named because it is spongelike with numerous cavities. It is located within the with numerous cavities. It is located within the medullary cavity and consists of extensively medullary cavity and consists of extensively connected bony trabeculae that are oriented along connected bony trabeculae that are oriented along the lines of the lines of stressstress. .

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

OSTEONOSTEON

Based on MaturityBased on Maturity

Immature boneImmature bone (primary bone (primary bone tissue): Immature bone is woven tissue): Immature bone is woven bone. bone.

Mature boneMature bone (secondary bone tissue) (secondary bone tissue) : Mature bone is characteristically : Mature bone is characteristically lamellar bone. Almost all bones in lamellar bone. Almost all bones in adults are lamellar bones.adults are lamellar bones.

WOVEN BONEWOVEN BONEThe earliest bone to be laidDown. Its histological structureshows the fibrils to be randomlyDistributedit is also knownas immature bone. A feature ofimmature bone is that itcontains a relatively higherproportion of osteocytes.

Woven bone (primary bone tissue)Woven bone (primary bone tissue)   It has the  collagen fibers are arranged in It has the  collagen fibers are arranged in

irregular random arrays.irregular random arrays. contain smaller amounts of mineral substance contain smaller amounts of mineral substance

and a higher proportion of osteocytes than and a higher proportion of osteocytes than lamellar bone. lamellar bone.

It is temporary, eventually converted to It is temporary, eventually converted to lamellar bone;lamellar bone;

This type of bone is also pathologic tissue in This type of bone is also pathologic tissue in adults.adults.

Except in a few places, such as areas near Except in a few places, such as areas near the sutures of the flat bones of the skull, tooth the sutures of the flat bones of the skull, tooth sockets , and the insertion site of some sockets , and the insertion site of some tendonstendons

Lamellar bone (secondary bone Lamellar bone (secondary bone tissue):tissue):

It is a mature bone with collagen It is a mature bone with collagen fibers that are arranged in lamellae.fibers that are arranged in lamellae.

In contrast to sponge bone, in In contrast to sponge bone, in compact bone, the lamellae are compact bone, the lamellae are concentrically organized around a concentrically organized around a vascular canal, termed a haversian vascular canal, termed a haversian canal. canal.

Lamellar Bone

Mature bone, alternativelydescribed as lamellar bone, ischaracterized by thecomparatively regulararrangement of its lamellaeand the presence of fewerosteocytes which are moreevenly arranged and arepresent in flat lacunae.

Based on developmental origin, Based on developmental origin,

Intramembranous bone (mesenchymal Intramembranous bone (mesenchymal bone):bone): Intramembranous bone develops Intramembranous bone develops from direct transformation of condensed from direct transformation of condensed mesenchyme. Flat bones are formed in this mesenchyme. Flat bones are formed in this way. way.

Intracartilaginous bone (cartilage bone, Intracartilaginous bone (cartilage bone, endochondral bone):endochondral bone): Intracartilaginous bone Intracartilaginous bone forms by replacing a reformed cartilage forms by replacing a reformed cartilage model. Long bones are formed in this waymodel. Long 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 is Each is a long, often bifurcated, cylinder that is

parallel to the long axis of bone, formed by parallel to the long axis of bone, formed by successive deposition of 4-20 (average 6) successive deposition of 4-20 (average 6) concentric layers of lamellae. concentric layers of lamellae.

Collagen fibers are parallel to each other within Collagen fibers are parallel to each other within each lamella,and they are oriented each lamella,and they are oriented perpendicularly to the fibers in the neighboring perpendicularly to the fibers in the neighboring lamellae. lamellae.

The haversian canals connect with each The haversian canals connect with each other by transverse or oblique Volkmann other by transverse or oblique Volkmann canals.canals.

These communicate with the marrow These communicate with the marrow cavity and the periosteum to provide cavity and the periosteum to provide channels for the neurovascular system.channels for the neurovascular system.

Volkmann canals are not surrounded by Volkmann canals are not surrounded by concentric lamellae; rather, they perforate concentric lamellae; rather, they perforate the lamellae.the lamellae.

Interstitial lamellaeInterstitial lamellae

Interstitial lamellaeInterstitial lamellae are incomplete or fragmented are incomplete or fragmented osteons that are located between the secondary osteons that are located between the secondary osteons.osteons.

They represent the remnant osteons left from partial They 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 The mixture of interstitial lamellae and complete osteons produces a osteons produces a mosaic patternmosaic pattern. .

Thus, the age of the bone can be deduced from the Thus, 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 less Younger bone has more complete osteons and less interstitial lamellae in between the osteons. interstitial lamellae in between the osteons.

Lamellar deposition starts from the Lamellar deposition starts from the periphery, so that younger lamellae are periphery, so that younger lamellae are closer to the center of the system, and closer to the center of the system, and the younger systems have larger canals. the younger systems have larger canals.

Between the lamellae are lacunae that Between the lamellae are lacunae that contain the cell bodies and contain the cell bodies and canaliculi that hold the cytoplasmic canaliculi that hold the cytoplasmic processes of osteocytes. processes of osteocytes.

The age of bone also affects osteoclast The age of bone also affects osteoclast activity in bone resorption.activity in bone resorption.

Osteoclasts preferentially differentiate Osteoclasts preferentially differentiate and resorb bone on aged bone than they and resorb bone on aged bone than they do on young bonedo on young bone

Henriksen et alHenriksen et al,,

Circumferential lamellaeCircumferential lamellae

Circumferential lamellaeCircumferential lamellae are circular are circular lamellae that line the external lamellae that line the external surface of the cortex adjacent to the surface of the cortex adjacent to the periosteum and line the inner surface periosteum and line the inner surface of the cortex next to the endosteum. of the cortex next to the endosteum.

There are more outer than inner There are more outer than inner circumferential lamellae.circumferential lamellae.

ENDOTHELIAL ENDOTHELIAL CELLSCELLS

Cells on the surfaces of bloodvesselsSynthesize Type IV collagen andVEGFhas much more active roles inevents such as angiogenesis,wound repair and bone formaton.

OsteocytesOsteocytes

An osteoblast becomes an osteocyte An osteoblast becomes an osteocyte when the cell is encased by osteoid matrix.when the cell is encased by osteoid matrix.

   It synthesizes itself. Lacunae and It synthesizes itself. Lacunae and canaliculi form around the osteocyte and canaliculi form around the osteocyte and its cytoplasmic processes, respectively. its cytoplasmic processes, respectively.

An osteocyte lies in its own lacuna and An osteocyte lies in its own lacuna and contacts its neighboring osteocytes contacts its neighboring osteocytes cytoplasmically through canaliculi cytoplasmically through canaliculi

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

Osteocytes have reduced synthetic activity Osteocytes have reduced synthetic activity and are not capable of mitotic division.and are not capable of mitotic division.

They are actively involved with the They are actively involved with the maintenance of the bony matrix. maintenance of the bony matrix.

Some of the osteocytes die during Some of the osteocytes die during remodeling, remodeling,

but most, return to the state of but most, return to the state of osteoprogenitor cells or persist as osteoprogenitor cells or persist as osteocytes for a long timeosteocytes for a long time

OSTEOBLAST

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 Active osteoblasts depositing osteoid on the surface of a woven bone on the surface of a woven bone trabecula. trabecula.

Osteoblasts are columnar or cuboidal Osteoblasts are columnar or cuboidal shaped, with eccentric nuclei and shaped, with eccentric nuclei and perinuclear halo. perinuclear halo.

These cells also have polarity, with These cells also have polarity, with the cytoplasm toward the bone but the cytoplasm toward the bone but the nuclei at the end away from the the nuclei at the end away from the bone.bone.

multinucleated cells

largely responsible for bone resorption

Positive for Tartrate resistant acid phosphatase

OSTEOCLAST

OsteoclastsOsteoclasts They are probably derived from a monocytic-macrophage They are probably derived from a monocytic-macrophage

system and are responsible for bone resorption. system and are responsible for bone resorption.

They are multinucleated cells with fine, fingerlike They are multinucleated cells with fine, fingerlike cytoplasmic processes and are rich in lysosomes that cytoplasmic processes and are rich in lysosomes that contain tartrate-resistant acid phosphatase (TRAP). contain tartrate-resistant acid phosphatase (TRAP).

lie in resorption craters known as lie in resorption craters known as Howship lacunaeHowship lacunae on on bone surfaces or in deep resorption cavities called bone surfaces or in deep resorption cavities called Cutting Cutting conescones. .

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 Cells that express the full morphologic and functional properties of mature osteoclasts are known to be restricted properties of mature osteoclasts are known to be restricted to the surfaces of bones.(transmigration)to the surfaces of bones.(transmigration)

These transmigration on the bone These transmigration on the bone surface has been assumed to be for surface has been assumed to be for the purpose of bone resorption. the purpose of bone resorption.

Transmigration through bone tissues Transmigration through bone tissues of various cell types results in bone of various cell types results in bone diseases with an imbalance in bone diseases with an imbalance in bone remodeling that is caused by remodeling that is caused by excessive osteoclast resorption. excessive osteoclast resorption.

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

Osteoclasts or their committed precursors do not Osteoclasts or their committed precursors do not have receptors for parathyroid hormone. have receptors for parathyroid hormone.

The hormonal signal is mediated by osteoblasts.The hormonal signal is mediated by osteoblasts. However, osteoclasts do have receptors for However, osteoclasts do have receptors for

calcitonin. calcitonin. When in an active state, osteoclasts create an effect When in an active state, osteoclasts create an effect

that always predominates over that of osteoblasts that always predominates over that of osteoblasts because osteoclasts are three times more efficient because osteoclasts are three times more efficient at bone resorption than osteoblasts are at bone at bone resorption than osteoblasts are at bone deposition.deposition.

In balance, osteoclasts have a much shorter life In balance, osteoclasts have a much shorter life span than osteoblasts. span than osteoblasts.

Osteoclasts are rarely seen in routine histologic Osteoclasts are rarely seen in routine histologic sections of normal bone. sections of normal bone.

An increased number of osteoclasts is characteristic An increased number of osteoclasts is characteristic of diseases with increased bone turnover. of diseases with increased bone turnover.

Bone matrixBone matrix

Bone matrix consists of organic and Bone 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 of The organic component is composed of

collagen fibers with predominately type collagen fibers with predominately type I collagen (95%) and amorphous I collagen (95%) and amorphous material, including glycosaminoglycansmaterial, including glycosaminoglycans

Osteoid is uncalcified organic matrix. Osteoid is uncalcified organic matrix.

Inorganic matter represents about Inorganic matter represents about 50% of the dry weight of bone matrix, 50% of the dry weight of bone matrix,

composed of abundant calcium and composed of abundant calcium and phosphorusphosphorus

as well as smaller amounts of as well as smaller amounts of bicarbonate, citrate, magnesium, bicarbonate, citrate, magnesium, potassium, and sodium. potassium, and sodium.

Calcium forms hydroxyapatite crystals Calcium forms hydroxyapatite crystals with phosphorus but is also present in with phosphorus but is also present in an amorphous form.an amorphous form.

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

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

An increased amount of osteoid An increased amount of osteoid is seen in pathologic is seen in pathologic conditions in which the conditions in which the remodeling rate is accelerated remodeling rate is accelerated or in which the mineralization lag or in which the mineralization lag time is increasedtime is increased

Blood supply to bone

Bone cells is less than20 um away from ablood vessel70% of the bloodsupply to cortex arefrom nutrient arteriesCompensate from theperiosteal arteries inthe event of fracture

Blood supply of boneBlood supply of bone

Long bones Diaphyseal nutrient artery:: This is the most important supply of arterial This is the most important supply of arterial

blood to a long bone. blood to a long bone. One or 2 principal diaphyseal nutrient arteries One 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 and These arteries then divide into ascending and

descending branches and supply the inner two descending 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 metaphyseal and epiphyseal Numerous metaphyseal and epiphyseal arteries supply the ends of bones.arteries supply the ends of bones.

These blood vessels mainly arise from the These blood vessels mainly arise from the arteries that supply the adjacent joint, arteries that supply the adjacent joint, anastomose with the diaphyseal capillaries, anastomose with the diaphyseal capillaries, and terminate in and terminate in bone marrowbone marrow, cortical bone, , cortical bone, trabecular bone, and articular cartilage.trabecular bone, and articular cartilage.

In growing bones, these arteries are In growing bones, these arteries are separated by the epiphyseal cartilaginous separated by the epiphyseal cartilaginous plates. plates.

Periosteal arterioles: Several of these : Several of these vessels supply the outer layers of corticalvessels supply the outer layers of cortical bone bone

Large irregular bones, short bones, and flat Large irregular bones, short bones, and flat bonesbones

These bones receive a superficial blood supply from These bones receive a superficial blood supply from the periosteum, as well as frequently from large the periosteum, as well as frequently from large nutrient arteries that penetrate directly into the nutrient arteries that penetrate directly into the medullary bone. The 2 systems anastomose freely.medullary bone. The 2 systems anastomose freely.

Venous and lymphatic drainage of boneVenous and lymphatic drainage of bone Blood is drained from bone through veins that Blood is drained from bone through veins that

accompany the arteries and frequently leaves through accompany the arteries and frequently leaves through foramina near the articular ends of the bones. Lymph foramina 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 Nerves are most rich in the articular extremities of the long bones, vertebrae, and larger flat bones. the long bones, vertebrae, and larger flat bones.

Many nerve fibers accompany the blood vessels to Many nerve fibers accompany the blood vessels to the interior of the bones and to the perivascular the interior of the bones and to the perivascular spaces of the haversian canals.spaces of the haversian canals.

The periosteal nerves are sensory nerves, some of The periosteal nerves are sensory nerves, some of which are which are painpain fibers. fibers.

Therefore, the periosteum is especially sensitive to Therefore, the periosteum is especially sensitive to tearingtearing or tension.or tension.

Accompanying the arteries inside the bones are Accompanying the arteries inside the bones are vasomotor nerves, which control vascular vasomotor nerves, which control vascular constriction and dilationconstriction and dilation

EpiphysisEpiphysis

In the long bones, the epiphysis is the In the long bones, the epiphysis is the region between the growth plate or region between the growth plate or growth plate scar and the expanded growth plate scar and the expanded end of bone, covered by articular end of bone, covered by articular cartilage.cartilage.

An epiphysis in a skeletally mature An epiphysis in a skeletally mature person consists of abundant person consists of abundant trabecular bone and a thin shell of trabecular bone and a thin shell of cortical bone . cortical bone . 

Although an epiphysis is present at Although an epiphysis is present at each end of the long limb bones, each end of the long limb bones,

it is found at only one end of the it is found at only one end of the metacarpals (proximal first and distal metacarpals (proximal first and distal second through the fifth second through the fifth metacarpals), metatarsals (proximal metacarpals), metatarsals (proximal first and distal second through fifth first and distal second through fifth metatarsals), phalanges (proximal metatarsals), phalanges (proximal ends), clavicles, and ribs.ends), clavicles, and ribs.

The epiphysis is the location of secondary ossification The epiphysis is the location of secondary ossification centers during development. centers during development.

The structure of the epiphysis is more complex in bones The structure of the epiphysis is more complex in bones that are fused from more than one part during that are fused from more than one part during development.development.

Examples include the proximal and distal ends of the Examples include the proximal and distal ends of the humerus, femur, and vertebrae. humerus, femur, and vertebrae.

The proximal end of the humerus is developed from 3 The proximal end of the humerus is developed from 3 separate ossification centers, which later coalesce to form a separate ossification centers, which later coalesce to form a single epiphyseal mass.single epiphyseal mass.

In the proximal humeral epiphysis, one of the centers In the proximal humeral epiphysis, one of the centers forms the articular surface, and the other 2 become the forms the articular surface, and the other 2 become the greater and lesser tuberosities.greater and lesser tuberosities.

Carpal bones, tarsal bones, and the patella are also called Carpal bones, tarsal bones, and the patella are also called epiphysioid bones and are developmentally equivalent to and are developmentally equivalent to the epiphyses of the long bonesthe epiphyses of the long bones

Some bone tumors such as Some bone tumors such as chondroblastomachondroblastoma have a strong have a strong predilection for the epiphysis or predilection for the epiphysis or epiphysioid bones epiphysioid bones

MetaphysisMetaphysis This is the junctional region between the This is the junctional region between the

epiphysis and the diaphysis. epiphysis and the diaphysis. The metaphysis contains abundant The metaphysis contains abundant

trabecular bone, but the cortical bone trabecular bone, but the cortical bone thins here relative to the diaphysis. thins here relative to the diaphysis.

This region is a common site for many This region is a common site for many primary bone tumors and similar lesions. primary bone tumors and similar lesions. The relative predilection of The relative predilection of osteosarcomaosteosarcoma..

for the metaphyseal region of long bones for the metaphyseal region of long bones in children has been attributed to the rapid in children has been attributed to the rapid bone turnover due to extensive bone bone turnover due to extensive bone remodeling during growth spurts remodeling during growth spurts

OSSIFICATIONOSSIFICATION Bone tissue arises by Bone tissue arises by Intramembranous Intramembranous

ossification or by Endochondral ossificationossification or by Endochondral ossification. . In either case, the original or model tissue is In either case, the original or model tissue is

gradually destroyed and replaced with bone gradually destroyed and replaced with bone tissue. tissue.

Bone forms only by appositional deposition of Bone 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 Woven bone is initially formed and is then later converted to lamellar bone by later converted to lamellar bone by subsequent remodeling. subsequent remodeling.

Intramembranous ossificationIntramembranous ossification

Although it is the source of flat bones, this Although it is the source of flat bones, this process also contributes to the growth of process also contributes to the growth of short bones and thickening of long bones.short bones and thickening of long bones.

Interstitial membranous ossification takes Interstitial membranous ossification takes place within a condensation of place within a condensation of mesenchymal tissue. mesenchymal tissue.

The process begins when multiple groups The process begins when multiple groups of cells differentiate into osteoblasts in a of cells differentiate into osteoblasts in a primary ossification center. primary ossification center.

Osteoid is synthesized and then Osteoid is synthesized and then mineralized surrounding the osteoblasts, mineralized surrounding the osteoblasts, which then become osteocytes. which then become osteocytes.

When these ossification centers fuse, a When these ossification centers fuse, a loose trabecular structure known as loose trabecular structure known as primary spongiosa is formed.primary spongiosa is formed.

Subsequently, blood vessels grow into Subsequently, blood vessels grow into the connective tissue between the the connective tissue between the trabeculae.trabeculae.

Bone marrow stem cellsBone marrow stem cells from the from the circulating blood then give rise to circulating blood then give rise to hematopoietic cells.hematopoietic cells.

Intramembranous ossificationIntramembranous ossification . . Woven bone arises directly from the surrounding Woven bone arises directly from the surrounding

mesenchymal tissuemesenchymal tissue

GrowthGrowth and fusion of several ossification and fusion of several ossification centers eventually replace the original centers eventually replace the original mesenchymal tissue. mesenchymal tissue.

In flat bones, compact bone is formed at In flat bones, compact bone is formed at both the internal and external surfaces both the internal and external surfaces

marked predominance of bone deposition marked predominance of bone deposition over bone resorption, whereas a spongy over bone resorption, whereas a spongy pattern remains in the central portion. pattern remains in the central portion.

The endosteum and periosteum are The endosteum and periosteum are formed from layers of connective tissue formed from layers of connective tissue that are not undergoing ossificationthat are not undergoing ossification

Endochondral ossificationEndochondral ossification

Endochondral ossification is Endochondral ossification is responsible for the formation of the responsible for the formation of the short and long bones. short and long bones. 

This process takes place within a This process takes place within a hyaline cartilage model, which hyaline cartilage model, which provides a template of the shape of provides a template of the shape of the bone to be formed. 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, and are hypertrophic and degenerated, and then the intervening chondroid matrix is then the intervening chondroid matrix is calcified. calcified.

Second phase:Second phase: osteogenic buds, osteogenic buds, composed of osteoprogenitor cells and composed of osteoprogenitor cells and blood capillaries, invade the spaces left blood capillaries, invade the spaces left by the degenerating chondrocytesby the degenerating chondrocytes

Osteoblasts arise from osteoprogenitor Osteoblasts arise from osteoprogenitor cells and lay down a layer of rapidly cells and lay down a layer of rapidly mineralized osteoid on the surface of mineralized osteoid on the surface of calcified cartilage.calcified cartilage.

The complex structure of calcified The complex structure of calcified cartilage with overlying newly bone thus cartilage with overlying newly bone thus formed is known as the primary spongiosa, formed is known as the primary spongiosa,

which is later remodelled to become which is later remodelled to become lamellar bone (secondary spongiosa).lamellar bone (secondary spongiosa).

Calcified cartilage remnants are Calcified cartilage remnants are resorbed by chondroclasts,resorbed by chondroclasts,

which are structurally and functionally which are structurally and functionally equivalent to osteoclasts, except equivalent to osteoclasts, except that chondroclasts work on cartilage that chondroclasts work on cartilage rather than bone. rather than bone.

Thus, the cartilage model is gradually Thus, the cartilage model is gradually replaced by bone and marrow cavities replaced by bone and marrow cavities

Long bones are formed from cartilaginous modelsLong bones are formed from cartilaginous models. .

The primary ossification center is The primary ossification center is initiated by intramembranous initiated by intramembranous ossificationossification

that is produced by the deep portions that is produced by the deep portions of the perichondrium that surround the of the perichondrium that surround the diaphysis. diaphysis.

A bone collar is thus formed, blocking A bone collar is thus formed, blocking the nutrient diffusion and leading to the the nutrient diffusion and leading to the degeneration of internal chondrocytes. degeneration of internal chondrocytes.

The perichondrium then becomes the The perichondrium then becomes the periosteum, from which the periosteum, from which the osteogenic bud arises and penetrates osteogenic bud arises and penetrates the calcified cartilage matrix through the calcified cartilage matrix through passages that are created in the passages that are created in the bone collar by osteoclasts bone collar by osteoclasts

The primary ossification center The primary ossification center expands longitudinally and is expands longitudinally and is associated with the growth of the associated with the growth of the periosteal bone collar. periosteal bone collar.

Osteoclasts are activated at the Osteoclasts are activated at the beginning of the process, resorb the beginning of the process, resorb the bone at the center, and hence create bone at the center, and hence create the marrow cavity. the marrow cavity.

At a later stage of bone At a later stage of bone development, a secondary development, a secondary ossification center arises at the ossification center arises at the center of each epiphysis.center of each epiphysis.

Unlike primary ossification, which Unlike primary ossification, which expands in a longitudinal fashion, the expands in a longitudinal fashion, the secondary ossification center grows secondary ossification center grows in a radial fashionin a radial fashion

Furthermore, a bone collar is not Furthermore, a bone collar is not formed in the area of articular formed in the area of articular cartilage due to the absence of cartilage due to the absence of perichondrium in this area. perichondrium in this area.

Thus, the epiphysis of the chondroid Thus, the epiphysis of the chondroid model is replaced by bone tissue, model is replaced by bone tissue, except the articular cartilage and the except the articular cartilage and the epiphyseal cartilage. epiphyseal cartilage.

Epiphyseal cartilageEpiphyseal cartilage It is located between the epiphysis and the metaphysis and It is located between the epiphysis and the metaphysis and

is responsible for the longitudinal growth of bone. It can be is responsible for the longitudinal growth of bone. It can be divided into 5 zones, starting from the epiphyseal side of divided into 5 zones, starting from the epiphyseal side of cartilage, as follows: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, is a continuous process throughout life,

in which damaged bone is repaired, ion in which damaged bone is repaired, ion homeostasis is maintained, and bone is homeostasis is maintained, and bone is reinforced for increased stress.reinforced for increased stress.

In adults, the remodeling rate varies in In adults, the remodeling rate varies in different types of bones.different types of bones.

Trabecular bone is remodeled at a Trabecular bone is remodeled at a higher rate (25% per year) than that of higher rate (25% per year) than that of cortical bone (3% per year) in a healthy cortical bone (3% per year) in a healthy adult.adult.

Resorption and Deposition Normally balanced, and bone density is Normally balanced, and bone density is

maintained. maintained. A lytic lesion results when resorptive activity A lytic lesion results when resorptive activity

exceeds deposition activity in a pathologic state.exceeds deposition activity in a pathologic state. The The cement linecement line (reversal line) is evidence of (reversal line) is evidence of

previous remodeling activity and is formed by filling previous remodeling activity and is formed by filling of new bone in a previously resorbed cavity of new bone in a previously resorbed cavity

The cement line is strongly basophilic due to the The cement line is strongly basophilic due to the high content of inorganic matrix and is normally high content of inorganic matrix and is normally found in the haversian and interstitial systems of found in the haversian and interstitial systems of adult bone. adult bone.

The relative amount of cement lines corresponds to The relative amount of cement lines corresponds to the amount of remodeling that has occurred. the amount of remodeling that has occurred.

An entire remodeling cycle requires An entire remodeling cycle requires approximately 6 months.approximately 6 months.

  Although a cement line that results Although a cement line that results from normal remodeling is relatively from normal remodeling is relatively long and straight.long and straight.

an indented or mosaic pattern an indented or mosaic pattern indicates a pathologically indicates a pathologically accelerated remodeling processaccelerated remodeling process

DEFINITIONDEFINITION FRACTUREFRACTURE IS DEFINED AS ANY IS DEFINED AS ANY

BREAK IN THE CONTINUITY OF BREAK IN THE CONTINUITY OF THE BONE.IT IS USUALLY DUE TO THE BONE.IT IS USUALLY DUE TO DIRECT OR INDIRECT TRAUMA.DIRECT OR INDIRECT TRAUMA.

A FRACTURE OCCURING IN A A FRACTURE OCCURING IN A DISEASED BONE IS CONSIDERED DISEASED BONE IS CONSIDERED AS A AS A PATHOLOGICAL FRACTUREPATHOLOGICAL FRACTURE

Fracture FactsFracture Facts Fractures, or broken bones, are Fractures, or broken bones, are

extremely common. Approximately 6.8 extremely common. Approximately 6.8 million Americans break a bone each million Americans break a bone each year. On average, every person in the year. On average, every person in the United States will experience two broken United States will experience two broken bones over the course of a lifetime. bones over the course of a lifetime. 

How Do Bones Break?How Do Bones Break?

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

FRACTURE CLASSIFICATIONFRACTURE CLASSIFICATION

SIMPLE OR CLOSEDSIMPLE OR CLOSED:: A FRACTURE WHICH DOES NOT A FRACTURE WHICH DOES NOT

COMMUNICATE WITH THE EXTERIOR.COMMUNICATE WITH THE EXTERIOR.

OPEN OR COMPOUND FRACTUREOPEN OR COMPOUND FRACTURE:: FRACTURE WHICH COMMUNICATES FRACTURE WHICH COMMUNICATES

WITH THE EXTERIOR THROUGH A WITH 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 AS GREENSTICK—NO DISCONTINUITY AS

PERIOSTEUM INTACT SEEN IN SOFT BONES PERIOSTEUM 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 FRACTURE HEALING 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 THERE OCCURS AS THE BONE BREAKS THERE OCCURS BLEEDING AT THE FRACTURED ENDS BLEEDING AT THE FRACTURED ENDS DUE TO THE CAPPILARY BREAK OF DUE TO THE CAPPILARY BREAK OF THE HAVERSIAN SYSTEM.THE HAVERSIAN SYSTEM.

THERE OCCURS A CLOT FORMATION THERE OCCURS A CLOT FORMATION AND RELEASE OF BLOOD CELLS AND AND RELEASE OF BLOOD CELLS AND PROTEINS IN THIS AREA.PROTEINS IN THIS AREA.

..

THE HISTOCYTES, MAST CELLS THE HISTOCYTES, MAST CELLS AND THE POLYMORHS CLEAR AND THE POLYMORHS CLEAR THE DEBRIS AND BACTERIA IN THE DEBRIS AND BACTERIA IN THE AREA, LEADING TO THE AREA, LEADING TO FORMATION OF GRANULATION FORMATION 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 TISSUE THE GRANULATION TISSUE BRIDGES THE TWO BROKEN BRIDGES THE TWO BROKEN ENDS, THESE ENDS BECOME ENDS, THESE ENDS BECOME RARIFIED AND CALCIUM IS LAID RARIFIED AND CALCIUM IS LAID DOWN BETWEEN THE ENDS IN DOWN BETWEEN THE ENDS IN THE GRANULATION TISSUE AS THE 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 IN SIMILAR ACTIVITY OCCURS IN THE MEDULLARY CAVITY THE MEDULLARY CAVITY ALSO.THE CALLUS SO FORMED IN ALSO.THE CALLUS SO FORMED IN THE MEDULLARY CAVITY IS THE MEDULLARY CAVITY IS CALLED THE INTERNAL OR CALLED THE INTERNAL OR ENDOSTEAL CALLUS,ENDOSTEAL CALLUS,

CALLUSCALLUS THAT FORMED OUTSIDE IS THAT FORMED OUTSIDE IS

PAROSTEAL OR PAROSTEAL OR EXTERNAL EXTERNAL CALLUSCALLUS. THESE TWO CALLUSES . THESE TWO CALLUSES MEET TO UNITE THE BONES.AT MEET TO UNITE THE BONES.AT THIS STAGE THE BONE HAS THIS STAGE THE BONE HAS UNITED BUT IS NOT STRONG UNITED BUT IS NOT STRONG ENOUGH TO BE EXPOSED TO THE ENOUGH TO BE EXPOSED TO THE STRESS.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 OR THE SOFT CALLUS GETS HARDENED OR CONSLOIDATED BY DEPOSITION OF BONE CONSLOIDATED BY DEPOSITION OF BONE SALTS, CARRIED OUT BY THE OSTEOBLASTS.SALTS, CARRIED OUT BY THE OSTEOBLASTS.

THE MULTINUCLEATE OSTEOCLASTS COME THE MULTINUCLEATE OSTEOCLASTS COME IN THE ACTION AND CONTROL THE DENSITY IN THE ACTION AND CONTROL THE DENSITY OF BONE.OF BONE.

THE MEDULLARY CANAL IS REPRODUCED THE MEDULLARY CANAL IS REPRODUCED AND THE MARROW CELLS STAR APPEARING.AND THE MARROW CELLS STAR APPEARING.

THE BONE CELL HEALS BY FORMING NEW THE BONE CELL HEALS BY FORMING NEW BONE AND DOES NOT HAVE SCAR BONE AND DOES NOT HAVE SCAR FORMATIONFORMATION

Remodeling of boneRemodeling of bone . Multiple osteoclasts are sitting . Multiple osteoclasts are sitting

in the Howship lacunae, in the Howship lacunae, resorbing one side of a bony resorbing one side of a bony trabecula, while osteoblasts are trabecula, while osteoblasts are depositing new bone on the depositing new bone on the other side.other side.

Intramembranous ossificationIntramembranous ossification . . Woven bone arises directly from the surrounding Woven bone arises directly from the surrounding

mesenchymal tissuemesenchymal tissue

EFFECT OF ULTRASOUND ON EFFECT OF ULTRASOUND ON BONE HEALINGBONE HEALING

JW Busse et al. The effect of low-JW Busse et al. The effect of low-intensity pulsed ultrasound therapy intensity pulsed ultrasound therapy on time to fracture healing: a meta-on time to fracture healing: a meta-analysis. Canadian Medical analysis. Canadian Medical Association Journal 2002 166: 437-Association Journal 2002 166: 437-441. 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 BONE FACTORS AFFECTING BONE HEALINGHEALING

TYPE OF BONETYPE OF BONE- CANCELLOUS – - CANCELLOUS – HEAL FASTER AS HAVE HEAL FASTER AS HAVE ABUNDANT BLOOD SUPPLY.ABUNDANT BLOOD SUPPLY.

TYPE OF FRACTURETYPE OF FRACTURE-SPIRAL AND -SPIRAL AND OBLIQUE FASTER THAN OBLIQUE FASTER THAN TRANSVERSE, UPPER EXTREMITY TRANSVERSE, UPPER EXTREMITY FASTER , THAN LOWER LIMB.FASTER , THAN 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 FRACTURESBASIC PRINCIPLESBASIC PRINCIPLES::

1. ACHIEVE ANATOMICAL ALIGNMENT1. ACHIEVE ANATOMICAL ALIGNMENT 2. ASSURE CORRECT IMMOBILIZATION2. ASSURE CORRECT IMMOBILIZATION 3. IMPROVE CIRCULATION AT 3. IMPROVE CIRCULATION AT

FRACTURE SITEFRACTURE SITE 4. REDUCE PAIN AND INFLAMMATION4. REDUCE PAIN AND INFLAMMATION 5. PROVIDE NECESSARY 5. PROVIDE NECESSARY

COMPRESSION TO CALLUS COMPRESSION TO CALLUS STRETCHING THE RAW CALLUS.STRETCHING THE RAW CALLUS.

BASIC METHODSBASIC METHODS

A) REDUCTIONA) REDUCTION B) IMMOBILZATION- USING PLASTER B) IMMOBILZATION- USING PLASTER

OF PARISOF PARIS INTERNAL FIXATION- USING NAILS INTERNAL 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 of Biomechanics of Fracture and Fixation Fracture and Fixation

Forces Acting on Long BonesForces Acting on Long Bones ForceForce is a vector is a vector

(magnitude with (magnitude with direction)direction)

MomentMoment: Force : Force acting on a bone acting on a bone causing rotationcausing rotation

Moment ArmMoment Arm: lever : lever that force acts on that force acts on (some distance away (some distance away from center of from center of rotation)rotation)

Basic Forces Causing FractureBasic Forces Causing Fracture

CompressionCompression TensionTension Transverse LoadingTransverse Loading Torsion Torsion

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

Bending Compression Torsion

Combined Combined bending & bending & axial loadaxial load Oblique Oblique

fracturefracture Butterfly Butterfly

fragmentfragment

Forces Acting on ConstructForces Acting on Construct

StressStress = = Force/(Area force is Force/(Area force is acting on)acting 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 material removed material returns to original returns to original shapeshape

PlasticPlastic = residual = residual deformation after load deformation after load removedremoved

Yield PointYield Point = load = load when plastic when plastic deformation takes deformation takes placeplace

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 Moment of

InertiaInertia: further : further away material is away material is spread in an spread in an object, greater the object, greater the stiffnessstiffness

Stiffness and Stiffness and strength are strength are proportional to proportional to radiusradius

ViscoelasticityViscoelasticity Stress RelaxationStress Relaxation: :

Applied force with Applied force with constant displacement constant displacement Decrease in internal force Decrease in internal force as resistance decreasesas resistance decreases resistance decreases as resistance decreases as

fluid is forced from syringefluid is forced from syringe Trabecular BoneTrabecular Bone: :

Trabecular structure acts Trabecular structure acts as elastic component, as elastic component, Interstitial fluid thru Interstitial fluid thru porous matrix is viscous porous matrix is viscous componentcomponent Under higher loading rate Under higher loading rate

there is resistance to flow there is resistance to flow thus increased internal thus increased internal pressure thus increased pressure thus increased stiffness of bonestiffness of bone

ViscoelasticityViscoelasticity Increased resistance with Increased resistance with

increased loading rateincreased loading rate CreepCreep = under constant = under constant

load soft tissue will load soft tissue will continue to continue to graduallygradually deformdeform

If compressive force is If compressive force is applied slowly, syringe applied slowly, syringe offers little resistanceoffers little resistance

Increased rate of force, Increased rate of force, increased resistance to increased resistance to rate of motion of syringerate of motion of syringe

FatigueFatigue Cyclic LoadsCyclic Loads below failure level below failure level

progressive cracks progressive cracks failure failure 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 (-) to (+) in 2 dissimilar materials in conductive fluidconductive fluid

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/Healing Biomechanics Intact/Healing BoneBone

Hierarchical structureHierarchical structure Collagen embedded Collagen embedded

with apatitewith apatite Decreased modulus Decreased modulus

with decreased with decreased apatite:collagen ratioapatite:collagen ratio

Fibrils organized to Fibrils organized to resist forceresist force Fibers organized into Fibers organized into

lamellaelamellae Concentric Lemellae Concentric Lemellae

make an Osteonmake an Osteon

Strength/StiffnessStrength/Stiffness Strength proportional Strength proportional

to to densitydensity Modulus proportional Modulus proportional

to to densitydensity AgeAge: increased : increased

modulus, bending modulus, bending strength from child to strength from child to adult, then decreaseadult, then decrease

Holes/defectsHoles/defects weaken bone (round weaken bone (round better than square)better than square)

Strength proportional Strength proportional to to diameterdiameter

Strength/StiffnessStrength/Stiffness Strength proportional Strength proportional

to to densitydensity Modulus proportional Modulus proportional

to to densitydensity AgeAge: increased : increased

modulus, bending modulus, bending strength from child to strength from child to adult, then decreaseadult, then decrease

Holes/defectsHoles/defects weaken bone (round weaken bone (round better than square)better than square)

Strength proportional Strength proportional to to diameterdiameter

Biomechanics of Bone FxBiomechanics of Bone Fx Weakest in Weakest in

Tension, Strongest Tension, Strongest in Compressionin Compression

Pure Pure BendingBending TransverseTransverse Fx Fx

TorsionTorsion SpiralSpiral FxFx

ShearShear Oblique Oblique FxFx

ButterflyButterfly due to due to Bend + ShearBend + Shear

Smaller cross section Smaller cross section of bone fails 1of bone fails 1stst (distal 1/3 of tibia)(distal 1/3 of tibia)

OsteoperosisOsteoperosis decreased density of decreased density of

trebecular bonetrebecular bone decreased endosteal decreased endosteal

thickness of cortical thickness of cortical bonebone

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 between between fracture fragmentsfracture fragments

that is that is compatible compatible with with fracture fracture healing.healing.

Motion is below the Motion is below the critical strain levelcritical strain level of tissue repair.of tissue repair.

PromotesPromotes indirect indirect bone healing! bone healing! Examples:Examples:

IM nailsIM nails Bridge plateBridge plate External FixatorExternal Fixator

Absolute StabilityAbsolute Stability Compression Compression of twoof two anatomically anatomically

reduced reduced fracture fragmentsfracture fragments.. No displacementNo displacement of the fracture under of the fracture under

functional load.functional load. Promotes Promotes directdirect bone healing! bone healing! Examples:Examples:

Lag screwLag screw PlatePlate => compression, buttress, => compression, buttress,

neutralizationneutralization Tension bandTension band

Preload > external load => absolute Preload > external load => absolute stabilitystability

External load > preload => relative External load > preload => relative stabilitystability

External load >> preload => frank External load >> preload => frank instabilityinstability

Biomechanics of Implants:Biomechanics of Implants:Avoiding ProblemsAvoiding Problems

Cerclage Wire: strength proportional Cerclage Wire: strength proportional to diameterto diameter Solid wire sensitive to scratch/notch Solid wire sensitive to scratch/notch

(cable better)(cable better) Optimal no. of turns 4-8 when twistedOptimal no. of turns 4-8 when twisted

Screw fixationScrew fixation Rotary forces Rotary forces compression compression

between objects (inclined plane on between objects (inclined plane on spiral pulls object toward head)spiral pulls object toward head)

Four part construction: Four part construction: head, shaft, head, shaft, thread,thread, tiptip

Thread defined by Thread defined by root diameter, root diameter, threadthread diameter, pitchdiameter, pitch

ScrewsScrews Larger coreLarger core diameter diameter

has has higher resistancehigher resistance to fatigue & shear to 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 can support along its axis)axis) outer diameter, length of outer diameter, length of

engagement, shear engagement, shear strength/density of bonestrength/density of bone

ScrewsScrews TappingTapping

increase compressive increase compressive forces, decrease forces, decrease interface frictioninterface friction

Cyclic LoadingCyclic Loading: If : If plate is not tight plate is not tight enough to boneenough to bone Force transferred to Force transferred to

long axis of screwlong axis of screw Stress corrosion of Stress corrosion of

plate rubbingplate rubbing

Plates & Bending Plates & Bending failurefailure

Leaving gap opposite to the Leaving gap opposite to the plate makes it a fulcrum plate makes it a fulcrum

increased stress at holesincreased stress at holes avoid holes over fracture avoid holes over fracture

sitessites greater the span between greater the span between

screwsscrews less stiff less stiff more bendingmore bending

PrebendingPrebending

Femoral NailFemoral Nail Contact Forces Contact Forces

expand femur expand femur (hoop stresses) (hoop stresses) may cause it to may cause it to split if too largesplit if too large

Starting hole: too Starting hole: too medial, too medial, too anterioranterior

Initial curve of IM Initial curve of IM rod, rod stiffnessrod, rod stiffness

Femoral NailFemoral Nail Distal Fx:Distal Fx:

Longer moment arm of Longer moment arm of external force thus greater external force thus greater bending moment in rodbending moment in rod

Greatest area of stress in rod Greatest area of stress in rod (Fx site) is near screw holes (Fx site) is near screw holes (stress riser)(stress riser)

Locking screw supported only Locking screw supported only by corticesby cortices

Stiffness & strength to bend Stiffness & strength to bend decrease with lengthdecrease with length

Possible to nick border of Possible to nick border of rod hole w/ screw rod hole w/ screw accentuate fatigueaccentuate fatigue

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 Screws closer to the end of the nail expand the

zone of fxs that can be fixed at the expense of zone of fxs that can be fixed at the expense of construct stabilityconstruct stability

Intramedullary NailsIntramedullary Nails ““Internal Splint”, Load SharingInternal Splint”, Load Sharing Nail itself should resist bending and Nail itself should resist bending and

torsiontorsion The bone should resist axial loadingThe bone should resist axial loading Strength => wall thickness, diameter, Strength => wall thickness, diameter,

and materialand material stiffness => 4th power of the diameterstiffness => 4th power of the diameter Type of fracture –transverse, oblique, or Type of fracture –transverse, oblique, or

complex determines some stabilitycomplex determines some stability

Intramedullary NailsIntramedullary Nails Working lengthWorking length is area that spans is area that spans

fracture between points of fixation.fracture between points of fixation. In bending, In bending, stiffness stiffness inversely inversely

proportional to square of lengthproportional to square of length Torsional rigidityTorsional rigidity is inversely is inversely

proportional to lengthproportional to length

Intramedullary NailsIntramedullary Nails Gripping strength is resistance to Gripping strength is resistance to

slipping at bone-implant interface. slipping at bone-implant interface. Increased by increasing cortical Increased by increasing cortical contact. contact.

Nail can twist or slip with torsional Nail can twist or slip with torsional loading which allows angulationloading which allows angulation

Intramedullary NailsIntramedullary Nailsinterlockinginterlocking

Dynamic fixationDynamic fixation controls bending controls bending and rotation, but allows axial loadingand rotation, but allows axial loading

Static lockingStatic locking controls bending, controls bending, rotation, and axial loadingrotation, and axial loading

Intramedullary NailsIntramedullary Nailsinterlockinginterlocking

femoral splittingfemoral splitting starting pointstarting point length of proximal length of proximal

fragmentfragment initial curvatureinitial curvature stiffnessstiffness

Ex-FixEx-Fix Self-tapping pins Self-tapping pins local local

heat heat thermal necrosis & thermal necrosis & microcracking (thus microcracking (thus corrosion/fatigue)corrosion/fatigue)

Pin Micromotion Pin Micromotion bone bone resorption at interfaceresorption at interface Undersize hole 0.1 mm Undersize hole 0.1 mm

decr micromotiondecr micromotion Undersize >0.3 mm Undersize >0.3 mm incr incr

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 Add Sidebar at 90 degree plane also resist torsiontorsion

Biomechanics: Metals and Biomechanics: Metals and MethylmethacrylateMethylmethacrylate

IntroductionIntroduction Metallurgy= the art and science of Metallurgy= the art and science of

using metalsusing metals 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 Stress Stress = distribution of internal forces (= distribution of internal forces (stress = stress =

load / area) load / area) Strain Strain = = change in linear dimensions of a body change in linear dimensions of a body

resulting from the application of a force or loadresulting from the application of a force or load Toughness Toughness = = ability of a metal to absorb ability of a metal to absorb

energy by bending without breakage (area energy by bending without breakage (area under the stress-strain curve )under the stress-strain curve )

Creep Creep = = amount of deformation that a material amount of deformation that a material undergoes with time as it is subjected a undergoes with time as it is subjected a constant loadconstant load

Biomechanics ReviewBiomechanics Review Elastic modulus Elastic modulus = material’s stiffness, = material’s stiffness,

stress/strain, slope of stress-strain stress/strain, slope of stress-strain curvecurve

Plastic deformation Plastic deformation = permanent = permanent change in shape after load is removedchange in shape after load is removed

Yield stress Yield stress = stress at transition = stress at transition between elastic & plastic on stress-between elastic & plastic on stress-strain curvestrain curve

Ultimate stress Ultimate stress = maximum stress prior = maximum stress prior to ruptureto rupture

Stress-Strain CurveStress-Strain Curve

Biomechanics ReviewBiomechanics Review Brittle Brittle = sustains little or no permanent = sustains little or no permanent

deformation prior to failuredeformation prior to failure Ductile Ductile = can sustain large amounts of = can sustain large amounts of

permanent deformation prior to failurepermanent deformation prior to failure Viscoelasticity Viscoelasticity = = stress/strain behavior that stress/strain behavior that

is time-rate dependentis time-rate dependent (eg. (eg. elongation of elongation of ligament being more likely to occur with ligament being more likely to occur with slower loading conditionsslower loading conditions ) )

Fatigue Fatigue = structural failure from repetitive = structural failure from repetitive stresses below ultimate stressstresses below ultimate stress

Orthopaedic MetalsOrthopaedic Metals Alloy metals = mixtures of metallic Alloy metals = mixtures of metallic

and non-metallic elementsand non-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:

Crystalline Crystalline Densely packed atomic nuclei in Densely packed atomic nuclei in

ordered, repeating 3D patternordered, repeating 3D pattern Valence electrons flow easily between Valence electrons flow easily between

adjoining atomsadjoining atoms Accounts for high electrical and thermal Accounts for high electrical and thermal

conductivity, chemical reactivityconductivity, chemical reactivity

MetalsMetals 3 basic atomic 3 basic atomic

configurationsconfigurations Atoms fill 70-75% of Atoms fill 70-75% of

possible volumepossible volume

MetalsMetals Tightness of a metal’s crystalline Tightness of a metal’s crystalline

packing defines grain sizepacking defines grain size Smaller grain size = more homogeneous Smaller grain size = more homogeneous

and isotropic= greater strengthand isotropic= greater strength Larger grain sizes = insufficient fatigue Larger 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 Chromium forms oxide when exposed to environment = corrosion resistantenvironment = corrosion resistant

Steel receives nitric acid bath creating passive Steel receives nitric acid bath creating passive oxide layer = “stainless”oxide layer = “stainless”

1,000 to 1,000,000 times more corrosion 1,000 to 1,000,000 times more corrosion resistantresistant

Stainless SteelStainless Steel

Cold-workingCold-working Cold working after Cold working after

solidification can solidification can reduce grain sizereduce grain size

Most orthopedic Most orthopedic steel is cold-steel is cold-worked 30%worked 30%

Cold-forged= even Cold-forged= even better strengthbetter strength

Stainless SteelStainless Steel DisadvantageDisadvantage

Susceptible to crevice and stress Susceptible to crevice and stress corrosioncorrosion

Decreased pH, increased oxidation, and Decreased pH, increased oxidation, and accelerated corrosion occurs in crevices accelerated corrosion occurs in crevices in the metal, eg. Underside of screw head in the metal, eg. Underside of screw head on a plateon a plate

Stress corrosion crackingStress corrosion cracking Corrosion accelerates cracking, leading to Corrosion accelerates cracking, leading to

failure under lower than normal stress levelsfailure under lower than normal stress levels

Stainless SteelStainless Steel Main use in fractures and spinal Main use in fractures and spinal

fixationfixation Require strength only until healing is Require strength only until healing is

completecomplete Charnley stem Charnley stem

Cobalt-chromeCobalt-chrome Casted, forged, or cold Casted, forged, or cold

workedworked Chromium for Chromium for

corrosion resistancecorrosion resistance Easy to makeEasy to make Widely used:Widely used:

Any metal component Any metal component of many total jointsof many total joints

Fracture fixationFracture fixation F75 casted alloy for F75 casted alloy for

porous coatingporous coating

Cobalt-chromeCobalt-chrome Casted alloysCasted alloys

Difficult quality controlDifficult quality control Solidifying too slowly allows grains to grow too Solidifying too slowly allows grains to grow too

large= loses strengthlarge= loses strength Solidifying too fast traps gasses in Solidifying too fast traps gasses in

microstructure= stress risersmicrostructure= stress 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 grains Smaller grains

Cobalt-chromeCobalt-chrome Hot forging and cold working greatly Hot forging and cold working greatly

improve strengthimprove strength Among the strongest orthopaedic Among the strongest orthopaedic

implant alloys availableimplant alloys available Good for articulations, low wear Good for articulations, low wear

generates less metal debrisgenerates less metal debris

Cancer Risk After Metal on Metal and Cancer Risk After Metal on Metal and Polyethylene on Metal Total Hip Polyethylene on Metal Total Hip

ArthroplastyArthroplasty 579 Metal on metal (CoCr) from 1967 579 Metal on metal (CoCr) from 1967

to 1973to 1973 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 and Cancer Risk After Metal on Metal and Polyethylene on Metal Total Hip Polyethylene on Metal Total Hip

ArthroplastyArthroplasty Metal on poly wear 100x more than Metal on poly wear 100x more than

metal on metalmetal on metal Hundreds of billions of submicron Hundreds of billions of submicron

polyethylene particles are annually polyethylene particles are annually released from the polyethylene cupreleased from the polyethylene cup

Metal on metal wear is less than 10 Metal on metal wear is less than 10 mm3 per yearmm3 per year

ConclusionConclusion No statistically significant increases in cancer No statistically significant increases in cancer

risk for either grouprisk for either group

The incidence of the other forms of The incidence of the other forms of cancers did not differ significantly from cancers did not differ significantly from those in the general population. those in the general population.

The observed variation in the incidence of The observed variation in the incidence of different cancers among patients who had different cancers among patients who had total hip arthroplasty compared with the total hip arthroplasty compared with the general population suggests that factors general population suggests that factors other than total hip arthroplasty play a major other than total hip arthroplasty play a major role in cancer.role in cancer.

TitaniumTitanium Excellent Excellent

biocompatabilitybiocompatability Very resistant to Very resistant to

corrosioncorrosion Titanium oxide layer Titanium oxide layer

exceeds protection of exceeds protection of steel and cobalt (self steel and cobalt (self passivation)passivation)

Oxide surface well Oxide surface well tolerated by bone, tolerated by bone, integrate wellintegrate well

Primary alloy Primary 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 Scratches easily, these stress risers reduce

fatigue lifefatigue life 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 tissues High levels of Ti/Al found in joint fluid and tissues

when used as femoral headwhen used as femoral head

TitaniumTitanium Bottom Line: excellent resistance to Bottom Line: excellent resistance to

fatigue, but is extremely susceptible fatigue, but is extremely susceptible to wear and is highly notch sensitiveto wear and is highly notch sensitive

Commonly used for plates and Commonly used for plates and stems, but not good for bearing stems, but not good for bearing surfacesurface

Trabecular Tantalum MetalTrabecular Tantalum Metal TantalumTantalum

The most biocompatible, corrosion resistant element The most biocompatible, corrosion resistant element used in medical devicesused in medical devices

Pacemakers, wire, foil, mesh for nerve repair, femoral Pacemakers, wire, foil, mesh for nerve repair, femoral endoprosthesesendoprostheses

Tantalum vs. Trabecular BoneTantalum vs. Trabecular Bone

Similar stiffness and Similar stiffness and porosityporosity

Trabecular MetalTrabecular Metal

distinguished from current distinguished from current porous materials by itsporous materials by its uniformity and uniformity and

structural continuitystructural continuity StrengthStrength

– low stiffness– Toughness– resistance to fatigue failure– greater volumetric porosity 80% vs. 20-30%

Trabecular Metal -- AdvantagesTrabecular Metal -- Advantages Excellent bone and Excellent bone and

tissue ingrowthtissue ingrowth Implants with less Implants with less

rigidityrigidity Better frictional Better frictional

characteristicscharacteristics Direct polyethylene Direct polyethylene

intrusion into the intrusion into the metal substrate to metal substrate to eliminate backside eliminate backside wearwear

Trabecular Metal -- AdvantagesTrabecular Metal -- Advantages Excellent bone and Excellent bone and

tissue ingrowthtissue ingrowth Implants with less Implants with less

rigidityrigidity Better frictional Better frictional

characteristicscharacteristics Direct polyethylene Direct polyethylene

intrusion into the intrusion into the metal substrate to metal substrate to eliminate backside eliminate backside wearwear

Trabecular Metal -- Trabecular Metal -- DisadvantagesDisadvantages

No known track No known track record in total record in total jointsjoints

Bony in growth Bony in growth may make may make revisions extremely revisions extremely difficultdifficult

Trabecular Metal – Orthopaedic Trabecular Metal – Orthopaedic applicationsapplications

primary and revision hip and knee primary 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 Decreased bony ingrowth in

acetabulumacetabulum

Press-Fit Metal-Backed Alumina Press-Fit Metal-Backed Alumina Sockets: A Minimum 5-Year Followup Sockets: A Minimum 5-Year Followup

StudyStudy 234 consecutive alumina-on-alumina hip 234 consecutive alumina-on-alumina hip

replacements using a press-fit metal-backed replacements 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 revision 11 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 good Results were excellent in 148 hips (80.5%), very good

in 31 hips (17%), good in two hips (1%), and fair in in 31 hips (17%), good in two hips (1%), and fair in three hips (1.5%). three hips (1.5%).

Press-Fit Metal-Backed Alumina Press-Fit Metal-Backed Alumina Sockets: A Minimum 5-Year Followup Sockets: A Minimum 5-Year Followup

StudyStudy Radiologic data were documented for 134 Radiologic data were documented for 134

patients (143 hips). patients (143 hips). Three sockets (2%) had a complete and Three sockets (2%) had a complete and

nonprogressive radiolucent line less than 1-mm nonprogressive 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 acetabular Neither component migration nor acetabular

osteolysis were detected. osteolysis were detected. A press-fit metal-backed socket may offer a A press-fit metal-backed socket may offer a

good solution for alumina socket fixation good solution for alumina socket fixation when combined with a careful surgical when combined with a careful surgical technique of implantation.technique of implantation.

PMMAPMMA PolymerPolymer

Large molecule made from combo of smaller Large 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 powder PMMA 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

Injectable Injectable Delayed hardening, allows Delayed hardening, allows

vacuum/centrifuge and cement gun deliveryvacuum/centrifuge and cement 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 amount of cement, heat transfer to tissuetissue

Protein denature @ 56degC, bone Protein denature @ 56degC, bone necrosis @ 47degCnecrosis @ 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 Modulus of Elasticity less than the

metals, less than cortical bone, but metals, less than cortical bone, but greater than cancellous bonegreater than cancellous bone

Reaches ultimate strength within 24 Reaches ultimate strength within 24 hourshours

Strong in compression, weak in Strong in compression, weak in tension and sheartension and 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:Cement TechniqueCement Technique

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:Cement TechniqueCement Technique

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 dry Pack with adrenaline sponge, then dry

spongesponge Cement gun & pressurizationCement gun & pressurization Distal and proximal centralizersDistal and proximal centralizers Surface texture/coating of stem Surface texture/coating of stem

PMMA:PMMA:Cement TechniqueCement Technique

Centrifugation or vacuumCentrifugation or vacuum reduces porosity of cement by 50% vs. reduces porosity of cement by 50% vs.

hand mixhand mix Increases tensile strength 44% vs. hand Increases tensile strength 44% vs. hand

mixmix Reduction in voids increases strength and Reduction in voids increases strength and

decreases crackingdecreases cracking AntibioticsAntibiotics

Several reports of addition of Abx Several reports of addition of Abx weakening cementweakening cement

In general, therapeutic levels of Abx In general, therapeutic levels of Abx won’t change measurable properties won’t change measurable properties

100 Cemented Versus 100 100 Cemented Versus 100 Noncemented Stems With Comparison Noncemented Stems With Comparison

of 25 Matched Pairsof 25 Matched Pairs Two series of 100 consecutive primary Two series of 100 consecutive primary

total hip arthroplasties, (all 28 mm total hip arthroplasties, (all 28 mm heads)heads)

One cemented and two noncemented One cemented and two noncemented stems underwent revision for aseptic stems underwent revision for aseptic looseningloosening

Of unrevised hips, outcome data Of unrevised hips, outcome data statistically favored cemented, rather statistically favored cemented, rather than noncemented, stems. than noncemented, stems.

100 Cemented Versus 100 100 Cemented Versus 100 Noncemented Stems With Comparison Noncemented Stems With Comparison

of 25 Matched Pairsof 25 Matched Pairs The data for cemented and The data for cemented and

noncemented stems, respectively, noncemented stems, respectively, werewere excellent to good result in 97% versus excellent to good result in 97% versus

88%;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 and endosteal cavitation in 6% versus

12%. 12%.

100 Cemented Versus 100 100 Cemented Versus 100 Noncemented Stems With Comparison Noncemented Stems With Comparison

of 25 Matched Pairsof 25 Matched Pairs 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 outcome data also statistically favored cemented over noncemented stemsover noncemented 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 Midterm followup data for these concurrent total

hip arthroplasty series of a mid1980s design hip arthroplasty series of a mid1980s design revealed prevalence of mechanical failure of 1% revealed prevalence of mechanical failure of 1% for cemented stems and 4% for noncemented for cemented stems and 4% for noncemented stems. stems.

PROSTALACPROSTALAC A prospective study of 49 patients, 2-stage A prospective study of 49 patients, 2-stage

exchange arthroplasty for infected THA and exchange arthroplasty for infected THA and TKA using antibiotic-loaded acrylic cement TKA using antibiotic-loaded acrylic cement ((PROSTALACPROSTALAC) system with a variety of doses ) system with a variety of doses of tobramycin and vancomycin was of tobramycin and vancomycin was performed. performed.

The intra-articular concentrations of The intra-articular concentrations of tobramycin and vancomycin were measured tobramycin and vancomycin were measured at the time of removal of the at the time of removal of the PROSTALACPROSTALAC temporary spacer and reimplantation of a temporary spacer and reimplantation of a definitive joint arthroplasty prosthesis, at a definitive joint arthroplasty prosthesis, at a mean 118 days following initial implantation. mean 118 days following initial implantation.

TobramycinTobramycin The 95% confidence interval of the The 95% confidence interval of the

intra-articular concentration of intra-articular concentration of tobramycin (4.35-123.88 mg/L) was tobramycin (4.35-123.88 mg/L) was entirely above the breakpoint entirely above the breakpoint sensitivity limit for sensitive organisms sensitivity limit for sensitive organisms when at least 3.6 g of tobramycin was when at least 3.6 g of tobramycin was used per package of bone-cement used per package of bone-cement

Entirely below it when at most 2.4 g Entirely below it when at most 2.4 g was used. was used.

VancomycinVancomycin Vancomycin elution was not as goodVancomycin elution was not as good However, detectable levels were still However, detectable levels were still

present in most patients. There was a present in most patients. There was a statistically significant increase in the statistically significant increase in the elution of vancomycin when the dose elution of vancomycin when the dose of tobramycin was increased from at of tobramycin was increased from at most 2.4 g to at least 3.6 g. most 2.4 g to at least 3.6 g.

The dose of vancomycin in the cement The dose of vancomycin in the cement did not influence the elution of either did not influence the elution of either tobramycin or vancomycin. tobramycin or vancomycin.

ConclusionConclusion On the basis of these results, the use On the basis of these results, the use

of at least 3.6 g of tobramycin and 1 of at least 3.6 g of tobramycin and 1 g of vancomycin per package of g of vancomycin per package of bone-cement is recommended when bone-cement is recommended when antibiotic-loaded cement spacers are antibiotic-loaded cement spacers are used in 2-stage exchange used in 2-stage exchange arthroplasty for infected total hip and arthroplasty for infected total hip and knee arthroplasties.knee arthroplasties.