Jim, Tyler and Matt

DR. T

Overview

Phases of bone development Peak levels of bone Dysfunctional levels of bone

Phases of Bone Development

GrowthBirth to ~20 years oldBone formation outpaces resorption

○ Increased length, circumference, function, strengthTime of greatest bone mass growth

Modeling or Consolidation~20 to 30 years oldUpkeep of existing bone mass with small bone

mass growth○ At 95% peak bone mass (PBM) around age 18

PBM reached during this phase

Peak Bone Mass The amount of bony

tissue present at the end of skeletal maturation Skeletal mass increases

from 70-95 g at birth to 2400-3300 g in young adulthood

Typically reached in late 20’s

Important determinant of osteoporotic fracture risk Higher PBM = lower risk

of osteoporosis

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 PBMImpact and weight-bearing

exercises increase PBM the most

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

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.

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

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

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

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

References

http://www.niams.nih.gov/Health_Info/Bone/Bone_Health/bone_mass_measure.asp

http://www.webmd.com/osteoporosis/living-with-osteoporosis-7/causes

http://www.medicinenet.com/osteopenia/article.htm#osteopenia

http://www.webmd.com/osteoporosis/guide/bone-mineral-density