1. Bones Part 4
DR. T
Jim, Tyler and Matt

2. Overview Phases of bone development Peak levels of bone
Dysfunctional levels of bone

3. Phases of Bone Development
Growth
Birth to ~20 years old
Bone formation outpaces resorption
Increased length, circumference, function, strength
Time of greatest bone mass growth
Modeling or Consolidation
~20 to 30 years old
Upkeep of existing bone mass with small bone mass growth
At 95% peak bone mass (PBM) around age 18
PBM reached during this phase

4. Peak Bone Mass
The amount of bony tissue present at the end of skeletal maturation
Skeletal mass increases from g at birth to g in young adulthood
Typically reached in late 20’s
Important determinant of osteoporotic fracture risk
Higher PBM = lower risk of osteoporosis

5. Peak Bone Mass Affected by many different factors
Genetics determine the size and structure of skeleton
PBM is directly related to physical activity prior to reaching PBM
Impact and weight-bearing exercises increase PBM the most

6. Remodeling Phase ~30 years old to death Decrease of bone mass from PBM
Increased risk of fractures
Onset of bone loss can be delayed by physical activity
Rate of bone loss can be reduced by physical activity
Hormones and nutrition also play important roles
Typically the phase where dysfunctional levels are seen

7. Dysfunctional Levels of Bone
A bone mineral density (BMD) test performed with a dual-energy x-ray absorptiometry (DXA) machine can be used to find dysfunctional levels of bone
BMD results are compared to an ideal PBM of a healthy 30 year old adult
World Health Organization Definitions Based on Bone Density Levels
Level
Definition
Normal
Bone density is within 1 SD (+1 or −1) of the young adult mean.
Low Bone Mass (Osteopenia)
Bone density is between 1 and 2.5 SD below the young adult mean (−1 to −2.5 SD).
Osteoporosis
Bone density is 2.5 SD or more below the young adult mean (−2.5 SD or lower).
Severe (established) osteoporosis
Bone density is more than 2.5 SD below the young adult mean, and there have been one or more osteoporotic fractures.

8. Dysfunctional Levels of Bone
Normal: A healthy bone density
Low Bone Mass (Osteopenia): Bones show the beginning of bone loss, but not enough to be osteoporosis
Osteoporosis: Bones are weak and porous, and more likely to break
The National Osteoporosis Foundation estimates that 10 million people in the U.S. have osteoporosis and nearly 34 million more have osteopenia, which puts them at greater risk for osteoporosis

9. Osteopenia BMD 1-2.5 SD below mean
Characterized by an increase risk of fractures
Causes: inadequate intake of calcium and vitamin D, excessive alcohol consumption, smoking, physical inactivity, decreased hormones (menopause) and genetics
Symptoms don’t occur until there is a fracture

10. Osteoporosis BMD >2.5 SD below mean
White and Asian women past menopause are at the highest risk to develop
Causes are the same as osteopenia
Bones can become so weak and brittle that mild stresses such as bending over or coughing can cause a fracture
Most common fracture sites are hip, wrist and spine

11. Osteoporosis
Symptoms can include: easy bone fracture, loss of height, stooped posture and back pain due to fractured or collapsed vertebrae
Healthy diet and weight-bearing exercise can help prevent bone loss or strengthen already weak bones
Having a higher PBM lowers the risk of development

12. References