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
1
1b
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
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
6a
1
3
6b
Radial growth can occur at the
osteogenic layer of the periosteum
Classification of
Bones
4
7
Cuboidal Bones
Picture of the wrist (carpal) bones showing the cuboidal shape
which classifies them as short bones.
From Clinical Anatomy.
8
Irregular Bones
Sketch of a vertebral
body showing the
irregular bone structure.
Flat Bones
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
10a
10b
10c
6
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
Circumferential Lamellar Bone (a)
12a
Circumferential Lamellar Bone (b)
12b
13a
8
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
Vertebral Trabecular Bone
13e
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
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.
17
11
Material Properties of
Bone
Material Properties of Hard Tissues
18
Measuring Biomechanical Properties of Bone
19a
12
Effect of increasing strain rate on stress-strain relationship
for bone.
From Park and Lakes, Biomaterials: An Introduction.
Simplified three element
spring-dashpot model of
viscoelasticity.
19b
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.
21
13
Spiral fractures
result from bone
Regular forces on long bones induce a which fails in shear.
bending moment and a tensile force.
Failure is most likely to initiate in tension.
Radin, Practical Biomechanics for the Orthopaedic Surgeon.
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
REMODELING
Osteoclasts dissolve mineral & matrix.
Osteoblasts lay down collagen & minerals.
Remodeling cycle takes ~ 100 days.
23b
23c
23d
15
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 deter mine
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