Abstract

Background:Metabolic bone disease of prematurity (MBDP) 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 birth weight preterm infants receiving contemporary neonatal care.

Methods:tSOS was measured, using a quantitative ultrasound device and LLL, using an electronic neonatal knemometer and in the same limb, weekly, for a median period of 4 weeks (3-16 weeks) in 84 preterm infants. The median gestation and birth weight of infants was 26.8 weeks (23-35.2 weeks) and 869.5g (418-1481g) respectively.

Results:The initial tSOS and LLL were associated with gestation (r=0.42, p<0.001; r=0.76, p<0.001) and birth weight (r=0.23, p=0.038; r=0.93, p<0.001). Postnatally, tSOS decreased (r= -0.15; p=0.011) whereas the LLL increased (r=0.96; p<0.001) with age. The rate of postnatal change in LLL, but not the change 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 likely to be due to cortical thinning secondary to endocortical bone loss, and increase in LLL provides a new insight into long-bone development in preterm infants.