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Introduction:Bone Structure & Composition

Topics

* Mineralized Tissues* Macrostructure of Bones

Long BonesShort BonesFlat BonesIrregular Bones

* Bone Composition - Ultrastructure* Cortical Bone

Woven BoneLamellar BoneCircumferential Lamellar BonePrimary Osteonal BoneSecondary Osteonal Bone

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Topics (cont.)

* Trabecular Bone* Teeth* Material Properties of Hard Tissues* Structural Properties of Hard Tissues* Mechanical Properties of Trabecular Tissue* Contribution of Components to Whole Bone Strength* Viscoelastic Properties of Bone* Viscoelastic Model of Bone Properties* Bone as a Composite Material - Model 1* Bone as a Compostie Material - Model 2* Fatigue of Bone* Mechanical Properties of Whole Bones* Wolff's Law* References* In Class Problems

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Active Growth

Slow Loss

Rapid Loss

Continuing Loss

Age (in years)

Bo

ne

Mas

s

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Hematopoeisis - production of red blood cells

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Hematopoeisis -production of red blood cells

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Picture of a humerus: an example of a long bone, showing the trabecular bone, cortical bone, epiphysis, diaphysis, metaphysis, and medullary canal.From Clinical Anatomy.

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Cortical

Compact Trabecular

Spongy

Cancellous

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Radial growth can occur at theosteogenic layer of the periosteum

Classification of Bones

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Picture of the wrist (carpal) bones showing the cuboidal shape which classifies them as short bones.

From Clinical Anatomy.8

Cuboidal Bones

Sketch of a vertebral body showing the irregular bone structure.

Image of a skull showing both flat bones (calvaria) and irregular bones (facial bones). From Clinical Anatomy.

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Flat BonesIrregular Bones

Structural and Microstructural

Organization of Bone

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Schematic drawing of the hierarchical make-up of bone.From Park and Lakes, Biomaterials: An Introduction

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Schematic drawing of the microscopic and microstructural variations in bone types. From Orthopaedic Basic Science

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12aCircumferential Lamellar Bone (a)

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Circumferential Lamellar Bone (b)

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Blood Supply to Bone

Through central (Haversian) and perforating (Volkmann s) canals

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Lamellae adjacent to Haversian Canals serve as storage space for exchangeable calcium ions

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Electron micrographs of trabecular bone structure from (a) healthy adult showing plate and strut structure, and (b) aging, osteoporotic individual showing beam and strut structure. From Mosekilde, et al. 14a

Ver

tebr

al T

rabe

cula

r Bon

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Sketch of the typica femoral neck and head showing the compressive and tensile trabeculae as designated by Singh et al. Ward's triangle, an area of reduced trabecular density, is indicated with a W.

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Sketch of the compressive and tensile trabeculae compared to the anatomical cross-section of the proximal femur.

Sketch of the sagittal section of a molar tooth showing the various component materials.

From Park and Lakes, Biomaterials: An Introduction.

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Teeth

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Material Properties of Bone

Material Properties of Hard Tissues

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Measuring Biomechanical Properties of Bone

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Effect of increasing strain rate on stress-strain relationship for bone.

From Park and Lakes, Biomaterials: An Introduction. 19b

Simplified three element spring-dashpot model of viscoelasticity.

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Deformation response to load, as a function of time, for simple 3 elementviscolelastic model.

Simplified composite model of bone modeled with an isostrain condition.

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Regular forces on long bones induce a bending moment and a tensile force. Failure is most likely to initiate in tension.Radin, Practical Biomechanics for the Orthopaedic Surgeon.

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Spiral fractures result from bone which fails in shear.

Functional Adaptation of Bone

Bone remodeling occurs throughout life through a regulated process of osteoclast-mediated bone resorption coupled to osteoblast-mediated new bone formation

The Bone Bank:

Balance (BMD), Deposits (Formation), and Withdrawals (Resorption)

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Osteoclasts dissolve mineral & matrix.

Osteoblasts lay down collagen & minerals.

Remodeling cycle takes ~ 100 days.

REMODELING

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Wolf (1892):The shape of bone is determined only by the static stressing

(ISOSTATICS)...Only static usefulness and necessity or static superfluity determine

the existence and location of every bony element and consequently of the overall shape of the bone .

Wolf Law of Functional Adaptation

Structure Isostatics

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Trabecular bone structure of the femoral neck follows the principal stress trajectories at that location, as discovered byWolff in the 1800's.

From Park and Lakes, Biomaterials: An Introduction

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