The document discusses the structure and properties of bone tissue. It describes the different types of bones in the human body including long bones, short bones, flat bones, irregular bones, and sesamoid bones. It explains the composition of bone including organic components like collagen and inorganic components like calcium and phosphate. Cortical and cancellous bone are compared in terms of their structure, porosity, circulation, and mechanical properties. The biomechanical behavior of bone under various loading modes such as tension, compression, shear, torsion, bending, and combined loading is analyzed. Fracture, fatigue fracture, viscoelasticity, bone remodeling, and osteoporosis are also summarized.

1. Dr. Faizan siddiqui (PT)
Lecturer
School of Physiotherapy,
IPM&R, Dow University of Health Science, Karachi

2. Introduction
 Body’s hardest structures
 Most dynamic and metabolically active tissues in the
body
 Highly vascular tissue
 Response to change in mechanical demands
 Protect the vital organs and support the body
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3. Long Bones
 e.g. femur, tibia
 1 long dimension
 used for leverage
 larger and stronger
in lower extremity
than upper extremity
 have more weight to
support
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4. Short Bones
 e.g. carpals and
tarsals
 designed for strength
not mobility
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5. Flat Bones
 e.g. skull, ribs,
scapula
 usually provide
protection
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6. Irregular Bones
 e.g. vertebrae
 provide protection,
support and leverage
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7. Sesamoid Bones
 e.g. patella (knee cap)
 a short bone embedded within
a tendon or joint capsule
 alters the angle of insertion of
the muscle
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8. Bone Composition and Structure
 Cells
 Organic ECM 90% collagen& Gelatinous Ground
substance GAGs(glycosaminoglycans)…PG
 Inorganic component (minerals embedded in
collagen)
 Hard
 Rigid
 Organic component (collagen)
 Flexible
 Resilience
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9. Organic Components
(e.g. protien collagen
type I collagen)
Inorganic Components
(e.g., calcium and phosphate)
60%
(dry wt)
Volume 40%
H2O
(10%)
Vol: 25%
one of the body’s
hardest structures
viscoelastic
ductile
brittle
Biomechanical Characteristics of Bone - Bone Tissue
30%
(dry wt)
Vol: 35%
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10. Long Bone Structure
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epiphyseal plate
cartilage separating
metaphysis from epiphysis
epiphysis
proximal and distal
ends of a long bone
metaphysis
either end of diaphysis
filled with trabecular bone
diaphysis
shaft of bone

11. Membranes
 Outer periosteal layer
 Volkmann canals
 Inner, osteogenic layer
 osteoblasts
 endosteum
 lines the central
(medullary) cavity
filled with yellow fatty
marrow
 osteoblasts
 osteoclasts
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12. Macroscopic level
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cortical or compact bone
(porosity ~ 15%)
periosteum
outer cortical membrane
endosteum
inner cortical membrane
trabecular, cancellous,
or spongy, bone
(porosity ~70%)

13. Cortical bone
 Fundamental structural Unit,
osteon or haversian system
 weight bearing pillar
 Lamellae
 Central canal
 Lacunae (osteocytes)
 Caniculi
 ground substance… PGs
 Interstitial lamellae
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14. Cancellous bone
 Consisting of trabeculae
 Trabeculae align along lines
of stress
 Trabeculae contain
irregularly arranged
lamallae and osteo-cytes
interconnected by canaliculi
 No osteons present
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15. Cortical Cancellous
Physical
Description
Dense protective shell
Rigid lattice designed for
toughness; Interstices are
filled with marrow
Location
Around all bones,
beneath periosteum;
Primarily in the shafts
of long bones
In vertebrae, flat bones
(e.g. pelvis) and the ends
of long bones
% of
Skeletal
Mass
80% 20%
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16. Cortical Cancellous
First Level
Structure
Osteons Trabeculae
Porosity 5-15% 50-90%
Circulation
Slow circulation of
nutrients and waste
Haversian system allows
diffusion of nutrients and
waste between blood
vessels and cells; Cells
are close to the blood
supply in lacunae
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17. Biomechanical Properties of Bone
 General
 Nonhomogenous
 Anisotropic
 Strongest
 Stiffest
 Tough
 Little elasticity
 load-deformation curve
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18. Whole Bone
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Cortical bone

19. Bone Material
 stress-strain curve
 Cortical
 More stress
 Less strain
 Less tough
 Cancellous
 More strain
 More energy storage
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20. BIOMECHANICAL BEHAVIOR OF
BONE
 Anisotropy
 Cortical
 Cancellous
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tension
compression
trabecular
cortical
shear
tension
compression
0 2
0
0
1
0
0
5
0
1
5
0
Maximum Stress
(MPa)

21. BONE BEHAVIOR UNDER VARIOUS
LOADING MODES
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Compression Tension Shear Torsion Bending
SHEAR
TENSION
COMPRESSION
Stress
to
Fracture
(Bone is
strongest in
resisting
compression and
weakest in
resisting shear.)

22. Tension
 Main source of tensile load is
muscle
 Clinically, fractures occur at
cancellous bone
 tension can stimulate tissue growth
 fracture due to tensile loading is usually an
avulsion
 Osgood-Schlatter’s disease
 Heel spur
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23. Compression
 Clinically, compression fractures are commonly
found in the vertebrae
 Osteoporotic
cervical fractures
e.g., football, diving, gymnastics
lumbar fractures
weight lifters, gymnasts
spine is loaded in hyperlordotic position
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24. Shear
 Clinically, shear fractures seen in
cancellous bone
 Shear stress is greatest when the
angle of applied force is equal to
45
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25. Bending
 combination of tension and
compression
 Three point bending
 “boot top” fracture
 Four-point bending
 Fractures produced by both types of
bending are commonly observed
clinically, particularly in the long bones
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26. Torsion
 causes it to twist about an axis
 spiral fracture develop
from this load
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27. Combine loading
 Combined bending & axial load
 Oblique fracture
 Butterfly fragment
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28. Fracture
 Compression failure results in
general in a stable fracture
 Tension or shear may have
catastrophic consequences
 Fracture Healing
 Reactive Phase
 Reparative Phase
 Remodeling Phase
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29. Viscoelasticity
 Stiffer and sustains a higher load to
failure when loads are applied at
higher rate
 stores more energy before failure at
higher loading rates
 fracture:
 low-energy
 high-energy
 very high-energy
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30. elastic
region
plastic region
fracture/failure
Stress
(Load)
Strain (Deformation)
Dstress
Dstrain
ELASTIC & PLASTIC RESPONSES
•elastic thru 3%deformation
•plastic response leads to fracturing
•Strength defined by failure point
•Stiffness defined as the slope of the
elastic portion of the curve
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31. INFLUENCE OF MUSCLE ACTIVITY ON
STRESS DISTRIBUTION IN BONE
 Alters the stress distribution
 Decreases or eliminates
tensile stress on the bone by
producing
 compressive stress
 Neutralization
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32. Fatigue Fracture
 Repeated applications of a lower-magnitude
load
 Two main types:
1. Fatigue-type fracture (Caused by muscle
fatigue………. Fatigue theory)
1. Tension
2. Compression
2. Insufficiency-type fracture
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33. Fatigue process
 Fatigue process depends upon
 Load
 Repetitions
 Also frequency of loading
 Common sites
 Vertebrae
 Femoral head
 Proximal tibia
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34. Stages of fatigue fracture
 Crack Initiation
 Discontinuities result in points of increased local stress where
micro cracks form
 Often bone remodeling repairs these cracks
 Crack Growth (Propagation)
 If micro cracks are not repaired they grow until they
encounter a weaker material surface and change direction
 Final Fracture
 Occurs only when the fatigue process progresses faster
than the rate of remodeling
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36. Insufficiency-type fracture
 Due to normal muscular activity stressing the
bone
 Seen in post-menopausal and/or amenhorroeic
women whose bones are
 Deficient in mineral
 Reduced elastic resistance
 Occurs if osteoporosis or some other disease
weakens the bones
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37. BONE REMODELING
 Remodel in size, shape, and structure
 Bone gains or loses cancellous and/or cortical bone in
response to the level of stress sustained
 Wolff’s law
 the remodeling of bone is influenced and modulated by
mechanical stresses
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38. CHANGES IN BONE OVER TIME
ADULT YEARS
 Little change in length
 Most change in density
 Lack of use decreases density
 Decrease strength of bone
 Activity
 Increased activity leads to increased diameter, density,
cortical width and Ca
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39. Hormonal influence
 Estrogen to maintain bone minerals
 Previously only consider after menopause
 Now see link between amenorrhea and decreased
estrogen - Female Athlete Triad
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osteoporosis
disordered
eating
amenorrhea
low body fat
excessive training
low estrogen
levels

40. Bone Deposition
A response to regular activity
 regular exercise provides stimulation to maintain
bone throughout the body
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– tennis players and baseball pitchers
develop larger and more dense bones
in dominant arm
– male and female runners have higher
than average bone density in both
upper and lower extremities
– non-weightbearing exercise
(swimming, cycling) can have positive
effects on BMD

41. Bone Resorption
 lack of mechanical stress
 Calcium (Ca) levels decrease
 Ca removed through blood via kidneys
 increases the chance of kidney stones
 weightless effects (hypogravity)
 astronauts use exercise routines to provide stimulus
from muscle tension
 these are only tensile forces - gravity is compressive
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42. Osteoporosis is a disorder involving decreased
bone mass and strength with pain and one or
more fractures resulting from daily activity.
Osteoporosis
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43. Osteoporosis
• Type I (postmenopausal) osteoporosis affects
about 40% of women after age 50
• Type II (age-associated) osteoporosis affects
most women and men after age 70
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44. osteoporosis prevention
• postmenopausal hormone replacement
• adequate dietary calcium and vitamin D
• avoiding smoking and excessive
consumption of protein, caffeine, and alcohol
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