Bones Part 4 DR. T Jim, Tyler and Matt

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

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

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 PBM Impact 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