Bone Health and Assessment in Children

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Bone Health and Assessment in Children

• Virginia Stallings, MD
• The Childrens Hospital of Philadelphia
• University of Pennsylvania School of Medicine

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Overview

• Assessing bone health in children
• Quantitative Ultrasound (QUS)
• Dual Energy Xray Absorptometry (DXA)
• Peripheral Quantitative Computed Tomography
  (pQCT)
• DXA Distal Femur site
• Body Composition
• Development of a Calcium Food Frequency
  Questionnaire
• Vitamin D status

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Bone Health Assessment
Children are not little adults!
http//www.bowhouse.com.au
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Ultrasound Sites and Techniques
From Baroncelli 2008, Pediatric Research 62(3)
220-228.
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Principles of QUS

• Properties of the ultrasound wave (shape,
  amplitude) are altered by the material through
  which it passes in a way that is characteristic
  of the structural properties of the material
• Material density and biomechanical properties
  (elastic modulus, compressive strength) of bone
  influence QUS waves

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Principles of QUS

• Trabecular bone scatters energy of ultrasound
  waves
• Cortical bone absorbs energy of ultrasound waves

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Principles of QUS

• QUS applied to peripheral sites (calcaneus,
  phalanges, patella, radius, tibia)
• Most ultrasound devices use a transmitter and
  detector to measure attenuation of the ultrasound
  wave
• Critical angle reflectometry uses a single probe
  to measure the reflected wave as it travels along
  cortical bone and determine the speed of sound

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Speed of Sound
SoS speed of sound AD-SoS amplitude
dependent SoS BTT Bone transmission time
(independent of soft tissue)
From Baroncelli 2008, Pediatric Research 62(3)
220-228.
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Sunlight Omnisense

• Portable
• Versatile can measure radius or tibia
• Probe sizes for different ages/sizes
• Pediatric reference data from Israel

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QUS Pediatric Reference Data
Tibia
Radius
From Zadik et al. Osteoporosis International
(10)857-62, 2003
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Quantitative Ultrasound (QUS)

• Advantages
• Rapid assessment
• Radiation-free
• Inexpensive and portable
• Easily accessible measurement sites
• Can be used in subjects without sleep/sedation
• Limitations
• What are the bone properties (cortical vs
  trabecular) being measured?
• Is it stable within an individual, and predictive
  of fracture?

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Dual energy x-ray absorptiometry - DXA

• Bone Mass, gm
• Bone area, cm2
• Bone Density, gm/cm2

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Advantages of DXA

• Non-invasive test for measurement of BMD
• Rapid, safe, easily tolerated, very low radiation
  exposure
• Can assess bone density at different skeletal
  sites, both axial and peripheral
• Widely available (100,000 in operation)
• Excellent precision in children and adults

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Pediatric Applications for DXA

• Hologic infant software - Whole Body Scan
• Requires no movement (sleep or sedation)
• Clothing / swaddling material can affect body
  composition results
• No reference data for current generation of DXA
  scanners

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Pediatric Applications for DXA

• Infant Spine scans
• Not traditionally used for infants
• Rapid scan time
• Doesnt require sedation
• No body composition data, but clothing less of an
  issue

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Why do both DXA and QUS

• Tibia QUS is a measure of cortical bone
• DXA spine scan is an integrated measure of
  cortical and trabecular bone
• Studies of cortical and trabecular bone density
  changes during puberty stage suggest different
  effects in the 2 bone compartments

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Why do both DXA and QUS

• DXA can also be used for non-traditional
  measurement sites like the tibia to validate
  tibia QUS measurements
• DXA is widely available and used clinically for
  children and adults, so study results may have
  greater clinical utility

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Puberty Effects on Tibia Trabecular and Cortical
Bone Density in Girls and Boys
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Other Measurement Sites
Distal Femur
Radius
Distal Femur
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Peripheral Quantitative Computed Tomography
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Peripheral Quantitative CT
Total Density Total Area
Cortical Density Cortical Area
Trabecular Density Trabecular Area
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Peripheral Quantitative CT
Muscle Cross Sectional Area
Cortical vBMD, dimensions and strength
Trabecular Total vBMD
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Distal Femur DXA Scan

• Indicated for
• Children with contractures
• Indwelling hardware that would interfere with a
  spine or total body scan
• Anomalies that would interfere with scan analysis
  or interpretation at standard sites
• Might be especially useful for immobilized
  children who may be at increased risk of femur
  fractures

Zemel et al J Clin Dens 2009 (in press)
Henderson et al AJR Am J Roentgenol 178439
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Development of the Calcium Counts Questionnaire

• Conducted by interview with the assistance of
  food models and probing by interviewer
• Recall over the previous 4 weeks because of the
  high intra-individual variability in calcium
  intake
• Quantitative FFQ based on serving size and
  frequency of intake
• First generation questionnaire
• Modified an existing calcium food-frequency
  questionnaire to capture foods that children
  usually eat based on recommendations of
  experienced pediatric research dietitians

Zemel et al (in review)
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Development of the Calcium Counts Questionnaire

• Second generation questionnaire
• Reviewed results of several hundred first
  generation questionnaires
• Dropped items that were never selected
• Reviewed the CSFII data for African Americans and
  Caucasians children identified the top 50
  sources of dietary calcium and added them to the
  questionnaire
• Panel of pediatric research dietitians reviewed
  several nutrient content sources and assigned
  calcium values to items by consensus

Zemel et al (in review)
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Validation of the Calcium Counts Questionnaire

• Compared results of the CCFFQ to 7-d weighed food
  diaries in 139 children 7 to 10 years of age
• Conducted a test-retest over a 1 month interval
  to determine reproducibility
• Concurrent validity was moderate (r0.61) and
  test-rest reliability was high (r0.74)
• CCFFQ, like most FFQs, overestimated calcium
  intake compared to weighed food record

Zemel et al (in review)
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Radiation Exposure
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Gender differences in body composition
From Butte et al. 2000 Ped Research 47(5)578-85
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Pea Pod (Air Displacement Plethysmograph)
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Pea Pod Infant Body Composition

• Uses air displacement to determine body volume
• With an accurate weight and volume measurement
  ?body density
• If assume that fat tissue has a constant density,
  ? body composition derived from body density ?
  fat-free mass, fat mass and percent body fat

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Pea Pod Infant Body Composition

• Rapid assessment
• Safe, reliable, accurate, provides immediate
  results
• Used up to measure infants up to 4 to 6 months
  of age (1 to 8kg 1kg)
• Length is the usual limtation

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SUMMARY

• Major advances in technology support bone health
  assessment in all ages
• Optimal reference data are limited
• Interpretation of results are complex in children
  with illness
• Stature, FFM, velocity
• Not just age and gender

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