6 Osseous Tissue and Bone Structure

© 2011 Pearson Education, Inc.

PowerPoint® Lecture Presentations prepared byAlexander G. CheroskeMesa Community College at Red Mountain

6Osseous Tissue and Bone Structure


Section 1: An Introduction to Bones

• Learning Outcomes• 6.1 Classify bones according to their shapes,

identify the major types of bone markings, and explain the functional significance of surface features.

• 6.2 Identify the parts of a typical long bone, and describe its internal

structures.• 6.3 Identify the cell types in bone, and list their

major functions.• 6.4 Compare the structures and functions of

compact bone and spongy bone.


• Learning Outcomes • 6.5 Explain the process of appositional bone

growth.

• 6.6 Explain the mechanisms of endochondral ossification.

• 6.7 Explain the mechanisms of intramembranous ossification.

• 6.8 CLINICAL MODULE Discuss various abnormalities of bone formation and growth.



• Skeletal system components• Bones (206 total)

• Divisions1. Axial skeleton (126 bones)

• Bones of skull, thorax, and vertebral column

• Form longitudinal axis of body

2. Appendicular skeleton (80 bones)

• Bones of the limbs and girdles that attach them to the axial skeleton

• Cartilages

• Ligaments and other connective tissues


© 2011 Pearson Education, Inc.Figure 6 Section 1 1

Axial Skeleton(126 Bones) The axial skeletonconsists of thebones of the skull,thorax, and vertebralcolumn. Theseelements form thelongitudinal axis ofthe body.

The adult skeletalsystem, which can bedivided into the axialskeleton and theappendicular skeleton

The appendicularskeleton includesthe bones of thelimbs and thepectoral and pelvicgirdles that attachthe limbs to theaxial skeleton.

AppendicularSkeleton (80 Bones)


• Functions of the skeletal system• Support (support for body, attachment for soft

tissues)• Storage of minerals (calcium and phosphate)

• Calcium most abundant mineral in body (~2–4 lb)• 98% stored in bones

• Blood cell production (all formed elements of blood)• Protection (delicate tissues and organs surrounded

by bone)• Leverage (act as levers with skeletal muscles to

move body)



Module 6.1: Bone classification

• Six categories based on shape1. Flat bones

• Thin, roughly parallel surfaces• Examples: cranial bones, sternum

2. Sutural bones (Wormian bones)• Irregular bones formed between cranial bones• Number, size, and shape vary

3. Long bones• Relatively long and slender• Examples: various bones of the limbs


• Six categories based on shape (continued)4. Irregular bones

• Complex shapes

• Examples: vertebrae, bones of pelvis, facial bones

5. Sesamoid bones• Small, flat, and somewhat shaped like sesame seed

• Develop in tendons of knee, hands, and feet

• Individual variation in location and number

6. Short bones• Small and boxy

• Examples: bones of the wrist (carpals) and ankles (tarsals)



• Bone surface features• Also known as bone markings

• External and internal features related to functions• Elevations/projections for tendon and ligament

attachment

• Depressions/grooves/tunnels for blood vessels or nerves to lie alongside or penetrate



• Skull surface features• Canal or meatus (large passageway)

• Process (projection or bump)

• Sinus (chamber within bone, usually filled with air)

• Foramen (small rounded passageway)

• Fissure (elongated cleft or gap)



• Humerus surface features• Head (expanded proximal end that forms part of

joint)• Tubercle (small, rounded projection)• Sulcus (deep, narrow groove)• Tuberosity (small, rough projection; may occupy

broad area)• Diaphysis (shaft; elongated body)• Trochlea (smooth, grooved articular process)• Condyle (smooth, rounded articular process)



• Femur surface features• Trochanter (large, rough projection)• Head• Neck (narrow connection between head and

diaphysis)• Diaphysis• Facet (small, flat articular surface)• Condyle



• Pelvis surface features• Crest (prominent ridge)• Fossa (shallow depression or recess)• Line (low ridge; more delicate than crest)• Spine (pointed or narrow process)• Ramus (extension that makes angle with rest of

structure)



Module 6.1 Review

a. Define surface feature.

b. Identify the six broad categories for classifying a bone according to shape.

c. Compare a tubercle with a tuberosity.


Module 6.2: Typical long bone structure

• Long bone features• Epiphysis (expanded ends)

• Consist largely of spongy bone (trabecular bone)• Network of struts and plates• Resists forces from various directions and directs body

weight to diaphysis and joints

• Outer covering of compact bone• Strong, organized bone

• Articular cartilage• Covers portions of epiphysis that form articulations• Avascular and receives resources from synovial fluid


• Long bone features (continued)• Metaphysis (connects epiphysis to shaft)

• Diaphysis (shaft)• Contains medullary cavity (marrow cavity)

• Filled with marrow

• Red bone marrow (red blood cell production)

• Yellow bone marrow (adipose storage)


© 2011 Pearson Education, Inc.Figure 6.2 1 - 2

Coronal sections through a right femur, showing the boundaries of a long bone’s majorregions, plus the bone’s internal organization and how it distributes the forces appliedto the bone

The epiphysis(e-PIF-i-sis) is anexpanded areafound at each endof the bone.

The metaphysis(me-TAF-i-sis; meta,between) is a narrowzone that connectsthe epiphysis to theshaft of the bone.

The diaphysis(shaft) is long andtubular.

The epiphysis consistslargely of spongy bone,also called trabecularbone. Spongy boneconsists of an open networkof struts and plates thatresembles latticework witha thin covering, or cortex, ofcompact bone.

The medullary cavity(medulla, innermost part), ormarrow cavity, is a spacewithin the hollow shaft. Inlife, it is filled with bonemarrow, a highly vasculartissue. Red bone marrowis highly vascular andinvolved in the productionof blood cells. Yellowbone marrow is adiposetissue important in thestorage of energy reserves.

Compressionon medial

side of shaft

Tensionon lateral

side ofshaft

Body weight(applied force)

The wall of the diaphysisconsists of a layer ofcompact bone.

Metaphysis

Epiphysis


• Bone vasculature• Growth and maintenance requires extensive blood

supply• Vascular features

• Nutrient artery/vein (commonly one each/bone)• Nutrient foramen (tunnel providing access to marrow

cavity)• Also supplies osteons of compact bone with blood

• Metaphyseal artery/vein• Carry blood to/from metaphysis• Connects to epiphyseal arteries/veins


© 2011 Pearson Education, Inc.Figure 6.2 3

A longitudinal section of the humerus, showing the extensive|network of blood vessels in long bones

Epiphyseal arteryand vein

Metaphysis

An articular cartilage covers portions ofthe epiphysis that articulate with other bones. The cartilage is avascular, and itrelies primarily on diffusion from thesynovial fluid to obtain oxygen andnutrients and eliminate wastes.

The metaphyseal artery (red) andmetaphyseal vein (blue) carry blood toand from the area of the metaphysis and tothe epiphysis through epiphyseal arteriesand veins.

Periosteum

Compactbone

Medullarycavity

MetaphysisMetaphyseal

artery and vein

Most bones have only onenutrient artery (shown inred) and one nutrient vein(shown in blue), but a fewbones, including the femur,have more than one of each.

A nutrient foramen is a tunnel that penetrates thediaphysis and providesaccess for the nutrient arteryand/or vein. Branches ofthese large vessels supplythe osteons of thesurrounding compact bonebefore entering andsupplying the tissues of themedullary cavity.


• Periosteum features• Smaller blood vessels (supply superficial

osteons)

• Lymphatic vessels (collect lymph from bone and osteons)

• Sensory nerves (innervate diaphysis, medullary cavity, and epiphyses)



Module 6.2 Review

a. List the major parts of a long bone.

b. Describe the function of the medullary cavity.

c. If articular cartilage is avascular, how is it nourished?


Module 6.3: Bone tissue

• Four bone cell types1. Osteocytes (osteo-, bone + cyte, cell)

• Mature bone cells that cannot divide• Most numerous bone cell type• Maintain protein and mineral content of adjacent

matrix• Dissolve matrix to release minerals• Rebuild matrix to deposit mineral crystals

• Occupy lacunae (pocket)• Separated by layers of matrix (lamellae)• Connected with canaliculi


• Four bone cell types (continued)

2. Osteoblasts (blast, precursor)• Produce new bony matrix (osteogenesis or

ossification)• Begins with release of proteins and other organic

components to produce unmineralized matrix (= osteoid)• Then assists in depositing calcium salts to convert

osteoid to bone

• Become osteocytes once surrounded by bony matrix



The layers of matrixare called lamellae(lah-MEL-lē; singular,lamella, a thin plate).

The structures of osteocytes and osteoblasts within along bone

Osteocytes account for mostof the cell population in bone.Each osteocyte occupies alacuna, a pocket sandwichedbetween layers of matrix.Osteocytes cannot divide,and a lacuna never containsmore than one osteocyte.

Narrow passagewayscalled canaliculipenetrate the lamellae,radiating through thematrix and connectinglacunae to one anotherand to various bloodvessels that supplynutrients.

Osteoblast

Osteoid



3. Osteoprogenitor cells (progenitor, ancestor)• Mesenchymal (stem) cells that produce cells

that differentiate into osteoblasts

• Important in fracture repair

• Locations• Inner lining of periosteum

• Lining endosteum in medullary cavity

• Lining passageways containing blood vessels




4. Osteoclasts (clast, to break)• Remove and remodel bone matrix

• Giant cells with 50+ nuclei• Derived from same stem cells as macrophages

• Release acids and proteolytic enzymes to dissolve matrix and release stored minerals • = Osteolysis (lysis, loosening)



Endosteum

Osteoprogenitor cell

Osteoclast

The structures of osteocytes and osteoblastswithin a long bone



• Bone matrix• Collagen fibers account for ~1/3 bone weight

• Provide flexibility

• Calcium phosphate (Ca3(PO4)2) accounts for ~2/3 bone weight

• Interacts with calcium hydroxide (Ca(OH)2) to form crystals of hydroxyapatite (Ca10(PO4)6(OH)2) salts

• Incorporates other salts (calcium carbonate, CaCO3) and ions (Na, Mg2, F)

• Provides strength



Module 6.3 Review

a. Define osteocyte, osteoblast, osteoprogenitor cell, and osteoclast.

b. How would the compressive strength of a bone be affected if the ratio of collagen to hydroxyapatite increased?

c. If osteoclast activity exceeds osteoblast activity in a bone, what would be the effect on the bone?


Module 6.4: Compact and spongy bone

• Compact bone• Functional unit is osteon

• Organized concentric lamellae around a central canal

• Osteocytes (in lacunae) lie between lamellae

• Central canal contains small blood vessels

• Canaliculi connect lacunae with each other and central canal

• Strong along its length


The structure of compact bone, as shown inthe shaft of a long bone

Capillary and venule

Central canal

Concentric lamellae

Canaliculi radiatingthrough the lamellaeinterconnect the lacunaeof the osteons with oneanother and with thecentral canal.

Endosteum

Periosteum

Central canal

VeinArtery

Osteon

Compact bone LM x 375

The osteocytes occupy lacunae that liebetween the lamellae. In preparing thismicrograph, a small piece of bone wasground down until it was thin enough totransmit light. In this process, the lacunaeand canaliculi are filled with bone dust, andthus appear black.

Circumferentiallamellae

Interstitiallamellae

Central canalPerforating canal



• Typical long bone organization• Periosteum (outermost layer)• Compact bone (outer bone tissue layer)

• Circumferential lamellae (circum-, around + ferre, to bear)• Outer and inner surfaces of compact bone layer

• Interstitial lamellae• Fill spaces between osteons

• Osteons• Contain central canals (parallel to bone surface)• Connected by perforating canals (perpendicular)

• Spongy bone (innermost layer)


• Spongy bone• Located where bones not heavily stressed or in

many directions• Lamellae form struts and plates (trabeculae)

creating an open network• Reduces weight of skeleton• No blood vessels in matrix

• Nutrients reach osteons through canaliculi open to trabeculae surfaces


© 2011 Pearson Education, Inc.Figure 6.4 3 – 4

Trabeculae ofspongy bone

Canaliculiopening on

surface

Endosteum Lamellae

The structure of spongy bone, as shown in the head of the femur


Module 6.4 Review

a. Define osteon.

b. Compare the structures and functions of compact bone and spongy bone.

c. A sample of bone has lamellae that are not arranged in osteons. Is the sample more likely from the epiphysis or from the diaphysis?


Module 6.5: Appositional bone growth

• Appositional bone growth• Increases bone diameter of existing bones

• Does not form original bones

• Osteoprogenitor cells differentiate into osteoblasts that add bone matrix under periosteum

• Adds successive layers of circumferential lamellae

• Trapped osteoblasts become osteocytes

• Deeper lamellae recycled and replaced by osteons

• Osteoclasts remove matrix at inner surface to enlarge medullary cavity


Increase in bone diameter resulting from appositional growth

Additional circumferentiallamellae are deposited, andthe bone continues toincrease in diameter.

Periosteum


Enlargement of the medullary cavity with increased bone diameterresulting from appositional growth

Bone matrix is removedby osteoclasts

Bone deposited bysuperficial osteoblastsInfant Child Young adult Adult


• Periosteum• Two layers

1. Fibrous outer layer

2. Cellular inner layer

• Functions1. Isolate bone from surrounding tissues

2. Route for blood and nervous supply

3. Actively participate in bone growth and repair



• Perforating fibers• Created by osteoblasts in periosteum cellular

layer

• Strongly connect tendons, ligaments, and joint capsules to bone through periosteum



Structure of the periosteum

Circumferentiallamellae

Fibrous layerof periosteum

Cellular layerof periosteum

Canaliculi

Osteocytein lacuna

Perforatingfibers


• Endosteum• Incomplete cellular layer lining medullary cavity

• Covers spongy bone and lines central canals

• Consists of simple layer of osteoprogenitor cells

• Where incomplete, osteoclasts and osteoblasts remodel matrix



Structure of the endosteum

Endosteum

Osteoclast

Circumferential lamella

Osteocyte

Osteoprogenitorcell

Osteoid

Osteoblast


Module 6.5 Review

a. Define appositional growth.

b. Distinguish between the periosteum and the endosteum.

c. As a bone increases in diameter, what happens to the medullary cavity?


Module 6.6: Endochondral ossification

• Initial bone formation in embryo begins with cartilage

• Replaced by bone through endochondral (endo-, inside + chondros, cartilage) ossification• Uses cartilage as small model• Bone grows in diameter and length

• Diameter growth involves appositional bone deposition

Animation: Early Endochondral Ossification


• Steps of endochondral ossification1. In shaft, chondrocytes enlarge and matrix ossifies

• Chrondrocytes die, leaving cavities within cartilage

2. Blood vessels grow around cartilage edge and osteoblasts form to create a superficial layer of bone

3. Blood vessels penetrate central region• Allow entering fibroblasts to change into osteoblasts

• Spongy bone produced (primary ossification center) and spreads toward bone ends



• Steps of endochondral ossification (continued)

4. Medullary cavity created as cartilage replaced by osseous tissue• Bone grows in length and diameter

5. Secondary ossification centers form as capillaries and osteoblasts migrate into epiphyses

6. Epiphyses fill with spongy bone • Only articular cartilage (on epiphyses) and

epiphyseal cartilage (in metaphysis) remain



The process of endochondral ossification

Enlargingchondrocytes within

calcifying matrix

Hyaline cartilage

Epiphysis

Diaphysis

Boneformation

Bloodvessel

Medullarycavity

PrimaryossificationcenterSuperficialboneSpongybone

Medullarycavity

Metaphysis

Enlargement ofchondrocytes

Formation of superficiallayer of bone

Production of spongy bone ata primary ossification center

Further growth in lengthand diameter

Hyaline cartilage

Epiphysis

Metaphysis

Periosteum

Compactbone

Secondaryossification

center

Formation of secondaryossification centers

Formation of an epiphysealcartilage between epiphysis

and diaphysis

Articular cartilage

Spongybone

Epiphysealcartilage

Diaphysis


• Steps of endochondral ossification (continued)7. Bone grows in length at epiphyseal cartilage

• Chondrocytes actively produce more cartilage on epiphysis side

• Osteoblasts actively replace cartilage with bone on shaft side

• As long as both processes are equally active, bone lengthening continues• At puberty, hormones increase bone growth and epiphyseal

cartilage is replaced• Leaves epiphyseal line in adults



Formation of an epiphysealcartilage between epiphysis

and diaphysis

Articular cartilage

Spongybone

Epiphysealcartilage

Diaphysis

Medullarycavity

Osteoblasts Osteoid

Epiphysealcartilage matrix

Cartilage cells undergoingdivision and secreting

additional cartilage matrix

The ossifying surface of anepiphyseal cartilage

LM x 250


Module 6.6 Review

a. Define endochondral ossification.

b. In endochondral ossification, what is the original source of osteoblasts?

c. How could x-rays of the femur be used to determine whether a person has reached full height?


Module 6.7: Intramembranous ossification

• Begins as mesenchymal (stem) cells differentiate into osteoblasts within embryonic or fibrous connective tissue

• Normally occurs in deeper layers of dermis• = Dermal bones (or membrane bones)

• Examples:• Roofing bones of skull• Lower jaw• Collarbone• Sesamoid bones such as patella


• Steps of intramembranous ossification• Mesenchymal cells secrete osteoid matrix

• Differentiate into osteoblasts

• Osteoid matrix becomes mineralized• Forms ossification center

• Bone grows out in small struts (spicules)• Osteoblasts become trapped and mature into

osteocytes• Mesenchymal cells produce more osteoblasts

• Blood vessels enter and become trapped in developing bone



Osteocyte in lacunaBone matrix

Osteoblast

Osteoid

Embryonic connective tissue

Mesenchymal cell

The process of intramembranous ossification

Bloodvessel

Osteocytesin lacunae

Osteoblastlayer

Blood vessel Osteoblasts Spicules Blood vessels

LM x 32 LM x 32

The growth of developing bone outward from the ossificationcenter in small struts called spicules

The growth and entrapment ofblood vessels within developingbone

Spongy bone, the initial form ofintramembranous bone


• Further membranous bone development• Spongy bone formed initially

• Remodeling around blood vessels forms osteons of compact bone

• Periosteum forms, lined with osteoblasts

• Begins at approximately 8th week of embryonic development



Futurehip bone

Primaryossification

centers of thelong bones ofthe lower limb

Intramembranousossification centers

that produce theroofing bones of

the skull

Long bonesof the limbs

10 weeks of development Flat bonesof the skull

16 weeks of development

The extent of intramembranous andendochondrial ossification occurring between10 and 16 weeks of development


Module 6.7 Review

a. Define intramembranous ossification.

b. During intramembranous ossification, which type(s) of tissue is (are) replaced by bone?

c. Explain the primary difference between endochondral ossification and intramembranous ossification.


• Endocrine and metabolic problems can affect the skeletal system• Disorders causing shortened bones

• Pituitary growth failure• Reduction in growth hormone leads to reduced epiphyseal

cartilage activity and short bones

• Rare due to treatment with synthetic growth hormone

• Achondroplasia• Epiphyseal cartilage grows unusually slowly

• Limbs are short

• Trunk is normal size

Module 6.8 CLINICAL MODULE: Abnormal bone growth and development




• Disorders causing lengthened bones• Marfan syndrome

• Excessive cartilage formation at epiphyseal cartilage

• Causes long, slender limbs• Other connective tissue abnormalities cause

cardiovascular issues

• Gigantism• Overproduction of growth hormone before

puberty





• Other skeletal growth abnormalities• Fibrodysplasia ossificans progressiva (FOP)

• Gene mutation that causes bone deposition around skeletal muscles• Bones developing in unusual places = heterotopic

(hetero, place) or ectopic (ektos, outside)

• Acromegaly• Growth hormone levels rise after epiphyseal plates

close• Bones get thicker

• Especially those in face, jaw, and hands





Module 6.8 CLINICAL MODULE: Review

a. Describe Marfan syndrome.

b. Compare gigantism with acromegaly.

c. Why is pituitary dwarfism less common today in the United States?


Section 2: Bone Physiology

• Learning Outcomes• 6.9 Discuss the effects of hormones on bone

development, and explain the homeostatic mechanisms involved.

• 6.10 CLINICAL MODULE Describe the types of fractures, and explain how

fractures heal.


• Bones are important mineral reservoirs• Mostly calcium but other ions as well

• Calcium • Most abundant mineral in body• 1–2 kg (2–4 lb)• ~99% deposited in skeleton• Variety of physiological functions

• Concentration variation greater than 30–35% affects neuron and muscle function

• Normal daily fluctuations are <10%


© 2011 Pearson Education, Inc.Figure 6 Section 2 1

Composition of Bone Bone Contains …

99% of the body’s calcium4% of the body’s potassium

35% of the body’s sodium50% of the body’s magnesium80% of the body’s carbonate99% of the body’s phosphate

Calcium 39%Potassium 0.2%

Sodium 0.7%Magnesium 0.5%Carbonate 9.8%Phosphate 17%

67%Total inorganiccomponents

Organiccompounds

(mostly collagen)33%

The importance of bones as mineral reservoirs


• Calcium (continued) • Levels controlled by activities of:

• Intestines• Absorb calcium and phosphate under hormonal control

• Bones• Remodeling by osteoblasts and osteoclasts

• Kidneys• Calcium and phosphate loss in urine under hormonal

control



Module 6.9: Hormonal control of calcium

• Factors that increase blood calcium levels• Parathyroid hormone (from parathyroid

glands)• Responses

• Bones: stimulates osteoclasts to release calcium

• Intestines: enhances calcitriol effects and increases calcium absorption

• Kidneys: increase release of hormone calcitriol, which causes calcium reabsorption in kidneys


• Factors that decrease blood calcium levels• Calcitonin from thyroid gland C cells

• Responses• Bone: decrease osteoclast activity

• Intestines: decreased absorption with decreasing PTH and calcitriol

• Kidneys: inhibits calcitriol release and calcium reabsorption



• As a calcium reserve, skeleton has primary role in calcium homeostasis

• Has direct effect on shape and length of bones• Release of calcium into blood weakens bones

• Deposit of calcium salts strengthens bones



Module 6.9 Review

a. Identify the hormones involved in stimulating and inhibiting the release of calcium ions from bone matrix.

b. What effect would increased PTH secretion have on blood calcium levels?

c. How does calcitonin lower the calcium ion concentration of blood?


Module 6.10 CLINICAL MODULE: Fractures

• Fracture• Crack or break due to extreme mechanical

stress

• Most heal as long as blood supply and cellular parts of periosteum and endosteum survive


• Steps of fracture repair

1. Large blood clot (fracture hematoma) develops

2. Calluses form• Internal callus (network of spongy bone uniting

inner edges)

• External callus (cartilage and bone stabilizes outer edges)




Animation: Steps in the Repair of a Fracture

• Steps of fracture repair (continued)

3. Calluses replaced and dead bone removed• Spongy bone unites broken ends

• Cartilage of external callus replaced by bone

4. Remodeling of healed bone


The events in the repair of a bone fracture

Spongy boneof internal

callus

Cartilageof external

callus

Fracturehematoma

Deadbone

Bonefragments

Spongy bone ofexternal callus

Periosteum

Internalcallus

Externalcallus

Externalcallus

Formation of a fracturehematoma

Formation of an internalcallus and an externalcallus

Replacement of thecartilage of the externalcallus with bone

Remodeling overtime andcompletion ofrepair


• Types of fractures• Categories

• Closed or simple (completely internal)• Only seen on x-rays

• Open or compound (project through skin)• More dangerous due to:

• Infection

• Uncontrolled bleeding



• Types of fractures (continued)• Transverse

• Break shaft across long axis

• Spiral• Produced by twisting stresses• Spread along length of bone

• Displaced• Produce new and abnormal bone arrangements• Nondisplaced retain normal alignment



• Types of fractures (continued)• Compression

• In vertebrae subjected to extreme stresses

• Greenstick• One side of shaft broken, one side bent

• Generally occurs in children

• Comminuted• Shatter affected area producing fragments



• Types of fractures (continued)• Epiphyseal

• Where bone matrix is calcifying

• A clean transverse fracture of this type heals well

• If not monitored, breaks between epiphyseal plate and cartilage can stop growth at site

• Pott• At ankle and affects both leg bones

• Colles• Break in distal radius



Transversefractures, such asthis fracture of theulna, break a boneshaft across its longaxis.

Types of Fractures

Spiral fractures,such as thisfracture of thetibia, are producedby twistingstresses thatspread along thelength of the bone.

Displaced fracturesproduce new andabnormal bone ar-rangements;nondisplacedfractures retain thenormal alignment ofthe bones orfragments.

Compression fracturesoccur in vertebraesubjected to extremestresses, such as thoseproduced by the forces thatarise when you land on yourseat in a fall.

In a greenstickfracture, such as thisfracture of the radius,only one side of theshaft is broken, andthe other is bent. Thistype of fracturegenerally occurs inchildren, whose longbones have yet toossify fully.

Comminutedfractures, such asthis fracture of thefemur, shatter theaffected area into amultitude of bonyfragments.

Epiphyseal fractures, such as thisfracture of the femur, tend to occur wherethen bone matrix is undergoing calcificationand chondrocytes are dying. A cleantransverse fracture along this line generallyheals well. Unless carefully treated, fracturesbetween the epiphysis and the epiphysealcartilage can permanently stop growth atthis site.

A Pottfracture occursat the ankle andaffects bothbones of the leg.

A Colles fracture, abreak in the distalportion of the radius,is typically the resultof reaching out tocushion a fall.


a. Define open fracture and closed fracture.

b. List the steps involved in fracture repair, beginning just after the fracture occurs.

c. When during fracture repair does an external callus form?


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6 Osseous Tissue and Bone Structure

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