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Relationship of tibial speed of sound and lower limb length to nutrient intake in preterm infants
  1. J Mercy1,
  2. B Dillon2,
  3. J Morris2,
  4. A J Emmerson1,
  5. M Z Mughal3
  1. 1Department of Neonatal Medicine, St Mary’s Hospital for Women and Children
    Manchester, UK
  2. 2Department of Medical Statistics, South Manchester University Hospitals Trust
    Manchester, UK
  3. 3Department of Paediatric Medicine, St Mary’s Hospital for Women and Children
    Manchester, UK
  1. Dr M Zulf Mughal, Department of Paediatric Medicine, St Mary’s Hospital for Women & Children, Hathersage Road, Manchester M13 0JH, England; zulf.mughal{at}


Background: Metabolic bone disease of prematurity is characterised by impaired postnatal mineralisation of the rapidly growing infant skeleton.

Objective: To longitudinally evaluate postnatal changes in tibial speed of sound (tSOS; which reflects cortical thickness and bone mineral density) and lower limb length (LLL; a measure of tibial growth) in very low birthweight preterm infants receiving contemporary neonatal care.

Methods: tSOS and LLL were measured using a quantitative ultrasound device and an electronic neonatal knemometer, respectively, in the same limb, weekly, for a median period of four weeks (3–16 weeks) in 84 preterm infants (median gestation 26.8 weeks (range 23–35.2 weeks) and median birth weight 869.5 g (range 418–1481 g)).

Results: Initial tSOS and LLL were correlated with gestation (r = 0.42, p<0.001; r = 0.76, p<0.001, respectively) and birth weight (r = 0.23, p = 0.038; r = 0.93, p<0.001, respectively). Postnatally, tSOS decreased (r = −0.15, p = 0.011) whereas LLL increased (r = 0.96, p<0.001) with age. The rate of postnatal change in LLL, but not in tSOS, was positively influenced by intake of calcium (p = 0.03), phosphorus (p = 0.01) and vitamin D (p = 0.03).

Conclusions: The postnatal decline in tSOS, which is probably due to cortical thinning secondary to endocortical bone loss, and increase in LLL provide new insight into the development of long bones in preterm infants.

  • quantitative ultrasound
  • speed of sound
  • lower limb length
  • knemometry
  • metabolic bone disease of prematurity

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  • The study was funded by St Mary’s Regional Neonatal Medical Unit Research Endowment Fund.

  • Competing interests: None.

  • Abbreviations:
    birthweight standard deviation score
    dual energy x ray absorptiometry
    generalised estimating equations
    metabolic bone disease of prematurity
    small for gestational age
    speed of sound
    tibial speed of sound