Introduction: Bone Structure & Composition

Transcription

1 Introduction: Bone Structure & Composition Topics * Mineralized Tissues * Macrostructure of Bones Long Bones Short Bones Flat Bones Irregular Bones * Bone Composition - Ultrastructure * Cortical Bone Woven Bone Lamellar Bone Circumferential Lamellar Bone Primary Osteonal Bone Secondary Osteonal Bone 1a 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 1b 1

2 Bone Mass Active Growth Slow Loss Rapid Loss Continuing Loss Age (in years) 2 Hematopoeisis - production of red blood cells 3 Hematopoeisis - production of red blood cells 4 2

3 5a 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. 5b Cortical Compact Trabecular Spongy Cancellous 6a1 3

4 6b Radial growth can occur at the osteogenic layer of the periosteum 7 Classification of Bones 4

5 Cuboidal Bones Picture of the wrist (carpal) bones showing the cuboidal shape which classifies them as short bones. From Clinical Anatomy. 8 Irregular Bones Flat 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. 9 Structural and Microstructural Organization of Bone 5

6 10a 10b 10c 6

7 10d Schematic drawing of the hierarchical make-up of bone. From Park and Lakes, Biomaterials: An Introduction 10e Schematic drawing of the microscopic and microstructural variations in bone types. From Orthopaedic Basic Science 11 7

8 Circumferential Lamellar Bone (a) 12a Circumferential Lamellar Bone (b) 12b 13a 8

9 Blood Supply to Bone Through central (Haversian) and perforating (Volkmann s) canals 13b 13c Lamellae adjacent to Haversian Canals serve as storage space for exchangeable calcium ions 13d 9

10 13e Vertebral Trabecular Bone 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 14b 10

11 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. 15 Sketch of the compressive and tensile trabeculae compared to the anatomical cross-section of the proximal femur. 16 Teeth Sketch of the sagittal section of a molar tooth showing the various component materials. From Park and Lakes, Biomaterials: An Introduction

12 Material Properties of Bone Material Properties of Hard Tissues 18 Measuring Biomechanical Properties of Bone 19a 12

13 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. Deformation response to load, as a function of time, for simple 3 element viscolelastic model. 20 Simplified composite model of bone modeled with an isostrain condition

14 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. Spiral fractures result from bone which fails in shear. 22 Functional Adaptation of Bone The Bone Bank: Balance (BMD), Deposits (Formation), and Withdrawals (Resorption) Bone remodeling occurs throughout life through a regulated process of osteoclast-mediated bone resorption coupled to osteoblast-mediated new bone formation 23a 14

15 REMODELING Osteoclasts dissolve mineral & matrix. Osteoblasts lay down collagen & minerals. Remodeling cycle takes ~ 100 days. 23b 23c 23d 15

16 23e Wolf Law of Functional Adaptation 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. Structure Isostatics 24a Trabecular bone structure of the femoral neck follows the principal stress trajectories at that location, as discovered by Wolff in the 1800's. From Park and Lakes, Biomaterials: An Introduction 24b 16