Catchy Title Up Here!

1
Paediatric bone densitometry reference data for
the Stratec XCT-2000 peripheral quantitative
computed tomography (pQCT) scanner
RL Ashby1 KA Ward1 SA Roberts2 MZ Mughal3 JE
Adams1 1Imaging Sciences, 2Biostatistics, The
University of Manchester 3CMMC University
Hospitals NHS Trust, Manchester
Figure 1 The non-dominant radius is measured at
4 and 50 of forearm length, from the growth
plate (A). Resulting cross-sectional pQCT images
at the (B) 50 and (C) 4 sites.
pQCT is being increasingly recognised as a
valuable tool for the study of healthy skeletal
development and for the assessment of paediatric
disorders associated with skeletal fragility.
Currently, there is a lack of reference data
using this technique in children and young
adults. The aim of this study was to produce
gender-specific centile charts for the clinical
interpretation of bone densitometry results in
children.
A pre-pubertal female aged 11.5 years whose
advanced stage cystic fibrosis treatment and
limited mobility placed her at increased risk of
skeletal fragility. Her pQCT measurements were
obtained and standard deviation scores for age
were calculated (table 1).
Subjects 379 healthy Caucasian children (203
male) mean age 123 (range 5-18) years were
studied. Height (cm) and weight (kg) were
measured and body mass index (kg/m2) calculated.
Bone densitometry assessment pQCT The Stratec
XCT-2000 pQCT scanner (Pforzheim, Germany) was
used to measure the non-dominant radius. One
slice was performed at the 4 distal metaphysis
and 50 midshaft diaphysis (Figure 1).
Measurements were made of total and trabecular
volumetric bone mineral density (vBMD, mg/cm3),
and bone area (mm2) at the distal radius and
cortical bone mineral content (cortical BMC
mg/mm), cortical area (mm2), cortical thickness
(mm) bone area at the midshaft radius. Data
analysis Gender-specific centile charts for pQCT
measurements of the distal and midshaft radius
were produced using the LMS method (Cole and
Green, 1992)(1).
This patients bone size at the distal radius is
reduced, most likely due to her short stature and
delayed puberty. Her trabecular vBMD is reduced,
which may indicate defective bone remodelling or
increased osteoclastic activity. Whilst bone area
is normal at the 50 radius, cortical BMC is
reduced. Low 4 radius trabecular vBMD, small
bone area and reduced cortical BMC may predispose
her to low trauma fractures. This patient
commenced cyclical three monthly infusions of
pamidronate to reduce her susceptibility to
fractures at axial and appendicular sites.
Centile charts Centile charts for 4 radius
total and trabecular vBMD (Figure 2), bone area
and all measured parameters at the 50 midshaft
radius (data not shown) by age were produced for
each gender.

• We have successfully produced the first
  UK-specific reference data for the Stratec
  XCT-2000 pQCT scanner.
• These data will assist in the interpretation of
  vBMD and bone geometric parameters of the radius
  in children aged 6-17 years.
• These pQCT data may be used with DXA(2)
  reference data to provide an enhanced evaluation
  of children who may have bone disorders.

1) Cole, TJ and Green, PJ (1992) Smoothing
reference centile curves the LMS
method and penalized likelihood. Stat Med, 11
1305-19. 2) Ward, K.A., Ashby, R.L. et al.
(2007) UK reference data for the Hologic QDR
DXA scanner in healthy children
aged 6-17 years. Arch Dis Child, 92 53-9.
Author email rebecca.ashby_at_manchester.ac.uk