2. The biology of bones
Our bones are comprised of living tissue, have
their own blood vessels, and are made of living
cells, which help them to grow and to repair
themselves.
Bones are in a perpetual state of remodelling
throughout life, with the entire skeleton being
replaced every 10 years!
3. The biology of bones
Bones are composed of two types of tissue:
1. A hard outer layer called cortical (compact) bone, which is
strong, dense and tough.
2. A spongy inner layer called trabecular (cancellous) bone. This
network of trabeculae is lighter and less dense than compact
bone.
Bone is also composed of:
• Bone forming cells (osteoblasts and osteocytes)
• Bone resorbing cells (osteoclasts)
• Nonmineral matrix of collagen and noncollagenous proteins
(osteoid)
• Inorganic mineral salts deposited within the matrix
4. The biology of bones
Bone cells
Cells in our bones are responsible for bone production, maintenance
and modelling:
• Osteoblasts: responsible for bone matrix synthesis and its
subsequent mineralization.
• Osteocytes: These cells are osteoblasts that become incorporated
within the newly formed osteoid, which eventually becomes calcified
bone. They are thought to be ideally situated to respond to changes
in physical forces upon bone and to transduce messages to cells on
the bone surface, directing them to initiate resorption or formation
responses.
• Osteoclasts: Function in the resorption of mineralized tissue and
are found attached to the bone surface at sites of active bone
resorption.
5. The biology of bones
Bone matrix
Osteoid is made by osteoblasts. It is gelatinous and is comprised
of type I collagen (~94%) and noncollagenous proteins.
Eventually becomes calcified. The hardness and rigidity of bone
is due to the presence of mineral salt in the osteoid matrix.
Calcified bone contains about 25% organic matrix, 5% water
and 70% inorganic mineral (hydroxyapatite).
6. The biology of bones
Bone Modelling
Modelling is when bone resorption and bone formation occur on
separate surfaces (i.e. formation and resorption are not coupled).
An example of this process is when long bone increases in length and
diameter. Bone modelling occurs during birth to adulthood and is
responsible for gain in skeletal mass and changes in skeletal form.
7. The biology of bones
Bone Remodelling
Remodelling is the replacement of old tissue by new bone tissue. This
mainly occurs in the adult skeleton to maintain bone mass. This process
involves the coupling of bone formation and bone resorption and
consists of five phases:
1. Activation: preosteoclasts are stimulated and differentiate under the
influence of cytokines and growth factors into mature active osteoclasts
2. Resorption: osteoclasts digest mineral matrix (old bone)
3. Reversal: end of resorption
4. Formation: osteoblasts synthesize new bone matrix
5. Quiescence: osteoblasts become resting bone lining cells on the newly
formed bone surface
8. The biology of bones
Bone Remodelling
Remodelling is the replacement of old tissue by new bone tissue. This
mainly occurs in the adult skeleton to maintain bone mass. This process
involves the coupling of bone formation and bone resorption and
consists of five phases:
1. Activation: preosteoclasts are stimulated and differentiate under the
influence of cytokines and growth factors into mature active osteoclasts
2. Resorption: osteoclasts digest mineral matrix (old bone)
3. Reversal: end of resorption
4. Formation: osteoblasts synthesize new bone matrix
5. Quiescence: osteoblasts become resting bone lining cells on the newly
formed bone surface
9. The function of bones
Bone plays a critical structural role in the body. Bone
also:
• supports the body
• facilitates movement
• protects internal organs
• produces blood cells
• stores and releases minerals and fat
10. What is Osteoporosis?
Osteoporosis is a chronic disease. An individual experiences low bone
mineral density which results in the bones becoming more fragile.
Osteoporosis leads to an increased risk of fracture, which can in turn
have an extreme impact on the quality of life due to ongoing pain,
reduced mobility, and loss of function/independence.
Osteoporosis is a ‘silent’ disease, as there is no pain until a fracture
occurs. As such it is under diagnosed and under treated.
11. What is Osteoporosis?
Basic pathogenetic mechanisms
Skeletal fragility can result from:
1. failure to produce a skeleton of optimal mass and strength
during growth
2. excessive bone resorption resulting in decreased bone mass
and microarchitectural deterioration of the skeleton
3. an inadequate formation response to increased resorption
during bone remodelling.
As we age, there is a reduction in hormone levels which can lead
to an imbalance in this bone rebuilding process which leaves
them thinner and more fragile
12. Fractures associated with
Osteoporosis
Osteoporotic Fragility Fracture or Minimal Trauma Fracture (MTF) is
defined as a fracture resulting from trauma equal to (or less than) a fall
from standing height.
A 10% loss in bone mass in the vertebrae can double the risk of
vertebral fractures and a 10% loss of bone mass in the hip can result in
a 2.5 times greater risk of hip fracture.
It has been well documented that following an MTF at any site, there is
a 2-4 fold increase in the risk of a subsequent fracture. Patients with a
history of prior fracture at any site should be evaluated for osteoporosis
and fracture risk
Only 20% of people who come to medical attention with osteoporotic
fractures are treated to prevent further bone loss and fractures.
13. Hip Fractures associated with
Osteoporosis
Most hip fractures occur following a fall and 90%
occur in people over 50.
Half of all patients who have had a hip fracture will
be unable to regain their previous independence and
will require some form of additional walking aid or
assistance with mobility
14. Osteoporosis Statistics
An estimated 1.2 million Australians have osteoporosis. Many remain
unaware that they are living with the condition.
The prevalence of osteoporosis increases with age, and it is estimated
that 80% of the population over 70 years have osteoporosis or
osteopenia.
Even after a fracture has occurred, up to 80% of people still go
undiagnosed and receive no treatment.
More than 50% of postmenopausal women over the age of 60 will
suffer one or more osteoporotic fragility fracture or minimal trauma
fracture during their remaining lifetime.
15. Osteoporosis Statistics
Why is osteoporosis undiagnosed and under-
treated?
• Limited awareness regarding the risks of osteoporosis by
both health professionals and the general public
• Lack of focus on osteoporosis compared to other chronic
diseases
• There is a mismatch between the burden of the
disease and its prioritisation in policy and resourcing
16. Increase awareness
Focus on early prevention
Osteoporosis is NOT simply a part of the normal ageing
process
People need to know what they can do to improve their bone
health
Be aware of modifiable risk factors
17. Risk Factors
The most common secondary cause of osteoporosis is long-term use
of corticosteroids, which are often used in the treatment of
respiratory disease (asthma), musculoskeletal conditions (rheumatoid
arthritis), inflammatory diseases and skin diseases
reducing bone formation and the viability of osteoblasts and
osteocytes.
Corticosteroids reduce intestinal calcium absorption and increase
renal calcium excretion. This may contribute to hyperparathyroidism
and bone loss. These negative effects on calcium balance can be
reversed with oral calcium and vitamin D3 supplementation
18. Risk Factors
Non modifiable:
• Family history of osteoporosis or fractures
• Age
Modifiable:
• Low vitamin D levels
• Low Calcium levels
• Low body weight
• Physical inactivity
• Smoking
• Excess alcohol consumption
Other:
• Malabsorption disorders (coeliac disease)
• Hormonal disorders (overactive thyroid or parathyroid)
• Early menopause
• Diabetes mellitus
• Hormonal treatments for breast cancer
19. Know Your Bones!
This is an evidence-based, consumer online health tool that
reviews risk factors for poor bone health by asking a series of
questions surrounding:
1. Medical history
2. Clinical risk factors
3. Lifestyle risk factors
4. Medication and supplement use
It also produces a summary report which you can discuss with
your GP.
https://www.knowyourbones.org.au/
20. Minimize your risk!
A healthy Lifestyle can more than halve a person’s risk of
suffering a fragility fracture.
• Eat a good diet with fruits and veg that is low in salt, has
adequate protein and calcium, and has optimal vitamin D.
• Aim to eat 1300mg of calcium per day form women
over 50 years
• Decrease alcohol consumption and stop smoking
• Regular weight bearing, physical exercise
• At least 30 minutes per day
• Moderate activities (for your heart, lungs and blood
vessels)
• Strength activities (to maintain bone strength)
• Flexibility activities (move more easily)
• Balancing activities (help prevent falls)
21. Calcium and Vitamin D
The keys to strong bones!
• Calcium is an important nutrient for building bone and
slowing the pace of bone loss.
• With age, the intestines absorb less calcium from the diet
and the kidneys seem to be less efficient at conserving
calcium. This can lead to your body ‘stealing’ calcium from
your bones.
• Vitamin D is calcium’s indispensable assistant.
• Helps the body absorb calcium
• Small amount of sun exposure can help body manufacture
its own vitamin D
• Fortified foods, or supplement
Talk to your GP if you think you need a supplement
22. The muscle-bone connection
Exercise affects your muscles and bones in similar ways. When
you work out regularly, your muscles get bigger and stronger.
The opposite occurs if you sit around and do nothing. The
same principle holds true for your bones.
Muscles and bones work together, so the changes in both of
them happen in tandem. Your body will maintain the right
balance, so as your muscles grow stronger from exercise, they
pull harder on your bones, and the harder they tug, the more
your bones will strengthen.
The bones that bear the load of the exercise will get the most
benefit. So if you only do upper body exercises, that will do
little for your lower body.
23. Yoga
It has been shown that a dozen yoga poses, performed daily,
may increase your bone density.
Scientific paper titled “Twelve-Minute Daily Yoga Routine
Reverses Osteoporotic Bone Loss”.
Yoga’s known benefits of improved balance and coordination
protect against falls (a major cause of osteoporotic fractures).
Also found that those who adhered to the daily program
significant increases in bone density in the spine, as well as
increased density in the hip as well.
None of the participants reported bone fractures or injuries
caused by doing yoga.
24. What is osteopenia?
Loss of bone density. If you think of bone mineral
density as a slope, normal would be at the top and
osteoporosis would be at the bottom. Osteopenia
would fall somewhere in between. In summary,
osteopenia is when your bones are weaker than
normal but not so far gone when compared to
osteoporosis.
25. Bone Density Scan
Diagnoses of osteoporosis (and osteopenia) is based on
measurement of bone mineral density (BMD).
Anyone over 50 with risk factors for osteoporosis warrants
investigation with a scan.
BMD is measured in g/cm² and expressed as a T-score.
• Normal: -1.0 or greater
• Osteopenia: -1.0 and -2.5
• Osteoporosis: equal or less than -2.5
• Severe osteoporosis: -2.5 or less AND 1+ osteoporotic fractures
26. Medicines
In patients with high fracture risk, especially those who have had
fractures, specific anti-osteoporosis therapy may be appropriate.
There are treatments covered by the PBS for high risk individuals.
Major component of anti-resorptive therapy are the bisphonates.
There are others available as well.
Hormone replacement therapy acts by restoring estrogen levels and
slow rate of bone loss.
Speak further with GP if you have questions.
27. More information is available on various
trustworthy websites
• www.osteoporosis.org.au
• www.womenshealth.gov
Information in this presentation is
adapted from
• National Strategic Action Plan for Osteoporosis 2019
• Osteoporosis Australia
• Sports Medicine Australia – Choose Health: Be Active
• International Osteoporosis Foundation
• Harvard Health Publishing: Healthbeat and Harvard Women’s Health Watch
