Bone Health and Assessment in Children
Virginia Stallings, MDThe Children’s Hospital of Philadelphia
University of Pennsylvania School of Medicine
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
Bone Health Assessment
http://www.bowhouse.com.au
Children are not
little adults!
From Baroncelli 2008, Pediatric Research 62(3): 220-228.
Ultrasound Sites and TechniquesPhalanges – IGEA Tibia – Sunlight Omnisense
Calcaneus – Sahara, Cuba
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
Principles of QUS
Trabecular bone scatters energy of ultrasound waves
Cortical bone absorbs energy of ultrasound waves
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
Speed of Sound
From Baroncelli 2008, Pediatric Research 62(3): 220-228.
SoS – speed of sound; AD-SoS – amplitude dependent SoS; BTT – Bone transmission time (independent of soft tissue)
Sunlight Omnisense
Portable Versatile – can
measure radius or tibia Probe sizes for different
ages/sizes Pediatric reference data
from Israel
QUS Pediatric Reference Data
From Zadik et al. Osteoporosis International (10):857-62, 2003
Tibia Radius
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?
Dual energy x-ray absorptiometry - DXA
• Bone Mass, gm• Bone area, cm2
• Bone Density, gm/cm2
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
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
Pediatric Applications for DXA
Infant Spine scans Not traditionally used for infants Rapid scan time Doesn’t require sedation No body composition data, but clothing less of an issue
AgeAll Study Subjects
Last 100 Subjects
6-12 mo 46/62 = 74% 25/31 = 81%
12-18 mo 26/35 = 74% 13/14 = 93%
18-24 mo 34/39 = 87% 25/26 = 96%
24-30 mo 34/36 = 94% 20/21 = 95%30-36 mo 32/33 = 97% 15/16 = 94%
Success Rate for Infant DXA Measurements Cincinnati Children's Medical Center
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
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
Puberty Effects on Tibia Trabecular and Cortical Bone Density in Girls and Boys
150
200
250
300
350
Tra
becu
lar
Den
sity, gm
/cm
3
1 2 3 4 5
F M F M F M F M F M
Breast / Genital Stage
900
1,0
00
1,1
00
1,2
00
1,3
00
Co
rtic
al D
en
sity, gm
/cm
3
1 2 3 4 5
F M F M F M F M F M
Breast / Genital Stage
Other Measurement Sites
Distal FemurRadius Distal Femur
Peripheral Quantitative Computed Tomography
Peripheral Quantitative CT
Cortical DensityCortical Area
Total DensityTotal Area
Trabecular DensityTrabecular Area
Cortical DensityCortical AreaBone Strength
Bone Strength Index =
(Moment of Inertia x Density)
Peripheral Quantitative CT
Muscle Cross Muscle Cross Sectional AreaSectional Area
Cortical vBMD, Cortical vBMD, dimensions and dimensions and strengthstrength
Trabecular & Trabecular & Total vBMDTotal vBMD
66%
38%
3%
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
Henderson et al AJR Am J Roentgenol ;178:439
Zemel et al J Clin Dens 2009 (in press)
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)
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)
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 (r=0.61) and test-rest reliability was high (r=0.74)
CCFFQ, like most FFQs, overestimated calcium intake compared to weighed food record
Zemel et al (in review)
Radiation Exposure
Source Effective Dose Equivalent (Sv)
Natural Radiation Sources
Natural background radiation at sea level 3,000 per year
Roundtrip transcontinental airplane flight 60 QCT
Peripheral QCT (Stratec 2000) < 0.01
Spine QCT 30 – 100 DXA (Hologic QDR-4500)
Lumbar spine 3.8
Lateral spine 1.4
Whole body 2.6 Hand-wrist x-ray 1 Ultrasound 0
Gender differences in body composition
From Butte et al. 2000 Ped Research 47(5):578-85
Pea Pod (Air Displacement Plethysmograph)
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
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
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