1. Bone Structure Cortical (Compact) Cancellous (trabecular, spongy)
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Bone Structure
Cortical (Compact)
Epiphysis (thin shell)
Diaphysis (shaft, thicker)
Cancellous (trabecular, spongy)
20% by mass, 80% by surface
5-70% density of cortical
30-90% porosity
Trabeculae
Plates and rods (~5 nm X 5 nm X 40 nm)
The epiphysis is the rounded end of a long bone, at its joint with adjacent bone(s). Between the epiphysis and diaphysis (the long midsection of the long bone) lies the metaphysis, including the epiphyseal plate (growth plate). At the joint, the epiphysis is covered with articular cartilage; below that covering is a zone similar to the epiphyseal plate, known as subchondral bone (see Wiktionary:subchondral).
The epiphysis is filled with red bone marrow, which produces erythrocytes (red blood cells).
The diaphysis is the main or mid section (shaft) of a long bone. It is made up of cortical bone and usually contains bone marrow and adipose tissue (fat).

2. Bone Composition Organic matrix Mineral phase
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Bone Composition
Organic matrix
50% by volume, 25% by weight
90% collagen (Type 1), 10% amorphous ground substance
Mineral phase
50% by volume, 75% by weight
Mostly calcium phosphate and calcium carbonate, a little magnesium, sodium and fluoride
Hydroxyapatite Ca10(PO4)6(OH)2 crystals and amorphous calcium phosphate
Hydroxylapatite, also called hydroxyapatite, is a mineral. It is a naturally occurring form of calcium apatite with the formula Ca5(PO4)3(OH), but is usually written Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two molecules. Hydroxylapatite is the hydroxyl endmember of the complex apatite group. The OH- ion can be replaced by fluoride, chloride or carbonate. It crystallizes in the hexagonal crystal system. It has a specific gravity of 3.08 and is 5 on the Mohs hardness scale. Pure hydroxylapatite powder is white. Naturally occurring apatites can however also have brown, yellow or green colorations, comparable to the discolorations of dental fluorosis.
Seventy percent of bone is made up of the inorganic mineral hydroxylapatite.[3] Carbonated-calcium deficient hydroxylapatite is the main mineral of which dental enamel and dentin are comprised. Hydroxyapatite crystals are also found in the small calcifications (within the pineal gland and other structures) known as corpora arenacea or 'brain sand'.
[edit] Medical uses
Hydroxylapatite can be found in teeth and bones within the human body. Thus, it is commonly used as a filler to replace amputated bone or as a coating to promote bone ingrowth into prosthetic implants. Although many other phases exist with similar or even identical chemical makeup, the body responds much differently to them. Coral skeletons can be transformed into hydroxylapatite by high temperatures; their porous structure allows relatively rapid ingrowth at the expense of initial mechanical strength. The high temperature also burns away any organic molecules such as proteins, preventing graft-versus-host disease (GVHD) and rejection.
Many modern implants, e.g hip replacements and dental implants, are coated with hydroxyapatite. It has been suggested that this may promote osseointegration and there is strong supporting evidence for this [4].

3. Bone Elastic Modulus, E Cortical Bone Trabecular Bone Y  0.076 GPa
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Bone Elastic Modulus, E
Cortical Bone
Y  17.9 GPa
ult  170 MPa (compression)
ult  120 MPa (tension)
Trabecular Bone
Y  GPa
ult  2.2 MPa (compression)
Note: Bone is non-homogeneous and orthotropic (spatial and direction dependence)
Why is there a difference in
compressive and tensile strength?

4. Wolff’s Law Human Anatomy, Second Edition, C.V. Mosby Company, 1976
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“Every change in the form and function of bones, or of their function alone, is followed by certain definite changes in their internal architecture and equally definite secondary alteration in their external conformation, in accordance with mathematical laws." Julius Wolff (1892)
Human Anatomy, Second Edition, C.V. Mosby Company, 1976

5. Bone Cells Osteoblasts – forming Osteocytes – maintaining
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Bone Cells
Osteoblasts – forming
Osteocytes – maintaining
Osteoclasts –resorbing
An osteoblast (from the Greek words for "bone" and "germ" or embryonic) is a mononucleate cell that is responsible for bone formation. Osteoblasts produce osteoid, which is composed mainly of Type I collagen. Osteoblasts are also responsible for mineralization of the osteoid matrix. Bone is a dynamic tissue that is constantly being reshaped by osteoblasts, which build bone, and osteoclasts, which resorb bone. Osteoblast cells tend to decrease as an individuals become elderly, thus decreasing the natural renovation of the bone tissue.[1]
Osteoblasts arise from osteoprogenitor cells located in the periosteum and the bone marrow. Osteoprogenitors are immature progenitor cells that express the master regulatory transcription factor Cbfa1/Runx2.
Osteoprogenitors are induced to differentiate under the influence of growth factors, in particular the bone morphogenetic proteins (BMPs). Aside from BMPs, other growth factors including fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), transforming growth factor beta (TGF-β) may promote the division of osteoprogenitors and potentially increase osteogenesis.
Once osteoprogenitors start to differentiate into osteoblasts, they begin to express a range of genetic markers including Osterix, Col1, ALP, osteocalcin, osteopontin, and osteonectin. Although the term osteoblast implies an immature cell type, osteoblasts are in fact the mature bone cells entirely responsible for generating bone tissue in animals and humans.
Osteoblasts that become trapped in the bone matrix become osteocytes. They cease to generate osteoid and mineralized matrix, and instead act in a paracrine manner on active osteoblasts. They are believed to act in a mechanosensory manner. (Citation Needed)
Osteoblasts (pointer) lining bone and osteocytes within lacunae of bone
Osteoblasts (pointer) lining bone
An osteoclast (from the Greek words for "bone" and "broken") is a type of bone cell that removes bone tissue by removing its mineralized matrix. This process is known as bone resorption. Osteoclasts and osteoblasts are instrumental in controlling the amount of bone tissue: osteoblasts form bone, osteoclasts resorb bone. Osteoclasts are formed by the fusion of cells of the monocyte-macrophage cell line.[1] Osteoclasts are characterized by high expression of tartrate resistant acid phosphatase (TRAP) and cathepsin K.
Osteoclast displaying many nuclei within its "foamy" cytoplasm
An osteoclast is a large cell that is characterized by multiple nuclei and a cytoplasm with a homogeneous, "foamy" appearance. This appearance is due to a high concentration of vesicles and vacuoles.[2][3] At a site of active bone resorption, the osteoclast forms a specialized cell membrane, the "ruffled border", which touches the surface of the bone tissue.[1] The ruffled border, which facilitates removal of the bony matrix, is a morphologic characteristic of an osteoclast that is actively resorbing bone. The ruffled border increases surface area interface for bone resorption. The mineral portion of the matrix (called hydroxyapatite) includes calcium and phosphate ions. These ions are absorbed into small vesicles (see endocytosis) which move across the cell and eventually are released into the extracellular fluid, thus increasing levels of the ions in the blood.

6. Mechanobiology Bone Remodeling
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Growth Rate 1
Optimal Bone Loading
Bone Remodeling
Resorption Rate 1
Equilibrium Zone
Signal
Bone Remodeling Signal
is function of:
 - microstrain magnitude
N - # of repetitions

7. Osteoporotic Bone (top and left)
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Osteoporotic Bone (top and left)
Dual energy X-ray absorptiometry (DXA, previously DEXA) is a means of measuring bone mineral density (BMD). Two X-ray beams with differing energy levels are aimed at the patient's bones. When soft tissue absorption is subtracted out, the BMD can be determined from the absorption of each beam by bone. Dual energy X-ray absorptiometry is the most widely used and most thoroughly studied bone density measurement technology.
Bone density (or bone mineral density) is a medical term referring to the amount of matter per square centimeter of bones.[1] Note that this is not a true "density", which would be measured in mass per cubic area. It is measured by a procedure called densitometry, often performed in the radiology or nuclear medicine departments of hospitals or clinics. The measurement is painless and non-invasive and involves minimal radiation exposure. Measurements are most commonly made over the lumbar spine and over the upper part of the hip.[2] The forearm is scanned if either the hip or the lumbar spine can't be. Average density is typicaly 3.88 g/cm2 in males and 2.90 g/cm2 in females. [3]
Terms
Results are often reported in 3 terms:
Measured density in g/cm2
z-score, the number of standard deviations above or below the mean for the patient's age, sex and ethnicity
t-score, the number of standard deviations above or below the mean for a healthy 30 year old adult of the same sex and ethnicity as the patient
[edit] Limitations
The technique has several limitations.
Measurement can be affected by the size of the patient, the thickness of tissue overlying the bone, and other factors extraneous to the bones.
Bone density is a proxy measurement for bone strength, which is the resistance to fracture and the truly significant characteristic. Although the two are usually related, there are some circumstances in which bone density is a poorer indicator of bone strength.
Reference standards for some populations (e.g., children) are unavailable for many of the methods used.
Crushed vertebrae can result in falsely high bone density so must be excluded from analysis.

8. Bone Elastic Modulus and Density
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Bone Elastic Modulus and Density
Elastic modulus can be estimated from density using a power law relationship
=2.5 for <1.2 g/cm3
=3.2 for >1.2 g/cm3
 = Tissue Mass/Bulk Volume
VT is the total or bulk volume of material, including the solid and void components
Reference: DR Carter, GS Beaupre, Skeletal Function and Form: Mechanobiology of Skeletal Development, Aging and Regeneration. Cambridge University Press 2007

9. Bone Mineral Density
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Can be measured using dual-energy X-ray absorptiometry (DEXA scanning)
2 X-ray beams
Relative amounts of X-ray beams blocked are determined
Measures are compared to age group norms
Bone Mineral Density
A bone mineral density (BMD) test measures the density of minerals (such as calcium) in your bones using a special X-ray, computed tomography (CT) scan, or ultrasound. This information is used to estimate the strength of your bones.
We all lose some bone mass as we age. Bones naturally become thinner (called osteopenia) as you grow older because existing bone is broken down faster than new bone is made. As this occurs, our bones lose calcium and other minerals and become lighter, less dense, and more porous. This makes the bones weaker and increases the chance that they might break (fracture).
With further bone loss, osteopenia leads to osteoporosis. So the thicker your bones are, the longer it takes to get osteoporosis. Although osteoporosis can occur in men, it is most common in women older than age 65.
If your bone density is lower than normal, you can take steps to increase your bone strength and reduce your chances of having a fracture. Some ways to increase bone density and strength include combining calcium and vitamin D supplements with weight-bearing exercise (such as walking), weight training (such as lifting weights or using weight machines, and using medicines such calcitonin (Miacalcin), alendronate (Fosamax), or risedronate (Actonel). After menopause, women can use hormone therapy and raloxifene (Evista) to increase bone density.
There are several different ways to measure BMD.
Dual-energy X-ray absorptiometry (DEXA). This is the most accurate way to measure BMD. It uses two different X-ray beams to estimate bone density in your spine and hip. Strong, dense bones allow less of the X-ray beam to pass through them. The amounts of each X-ray beam that are blocked by bone and soft tissue are compared to each other. DEXA can measure as little as 2% of bone loss per year. It is fast and uses very low doses of radiation but is more expensive than ultrasound testing. Single-energy X-ray absorptiometry (SXA) may be used to measure heel and forearm bone density, but SXA is not used as often as DEXA. See a picture of a DEXA X-ray of the hips or a DEXA X-ray of the spine.
Peripheral dual-energy X-ray absorptiometry (P-DEXA). P-DEXA is a type of DEXA test. It measures the density of bones in the arms or legs, such as the wrist-it cannot measure the density of the bones most likely to break, such as the hip and spine. P-DEXA machines are portable units that can be used in a doctor's office. P-DEXA also uses very low doses of radiation, and the results are ready faster than standard DEXA measurements. P-DEXA is not as useful as DEXA for finding out how well medicine used to treat osteoporosis is working.
Dual photon absorptiometry (DPA). This test uses a radioactive substance to measure bone density. It can measure BMD in your hip and spine. DPA also uses very low doses of radiation but has a slower scan time than the other methods.
Ultrasound. This test is generally used to look for problems. If results from an ultrasound test find low bone density, DEXA is recommended to confirm the results. Ultrasound uses sound waves to measure BMD, usually in your heel. Some machines pass the sound waves through air and some pass them through water. Ultrasound is quick, painless, and does not use potentially harmful radiation like X-rays. One disadvantage of ultrasound is it cannot measure the density of the bones most likely to fracture (the hip and spine) from osteoporosis. It is not used to keep track of how well medicine used to treat osteoporosis is working. More studies are being done to see if ultrasound is a reliable way to check bone density for osteoporosis.
Quantitative computed tomography (QCT). This is a type of CT scan that measures the density of a bone in the spine (vertebra). A form of QCT called peripheral QCT (pQCT) measures the density of bones in your arms or legs, usually your wrist. QCT is not usually used because it is expensive, uses higher radiation doses, and is less accurate than DEXA, P-DEXA, or DPA.
Before being screened for osteoporosis, you may want to think about what you will do if the tests show you have a high chance of getting osteoporosis. For more information, see:

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Types of Loading

11. 3 Point Bending Load Situations on Long Bones
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3 Point Bending Load Situations on Long Bones
Broken fibula ends season for Wisconsin TE Beckum
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The school announced on Sunday that tight end Travis Beckum fractured his left fibula against Illinois on Saturday and will miss the rest of the season. He underwent successful surgery on Saturday night at University of Wisconsin Hospital.
Which bone did Travis break?
Oct 27, 2008 (AP) ... Wisconsin tight end Travis Beckum suffered a fractured tibula on Saturday …
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12. Lab 5 – 3 Point Bending of Bones
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Lab 5 – 3 Point Bending of Bones