Quantifying bone strength deficits in young adults born extremely preterm or extremely low birthweight.

The long-term bone health of young adults born extremely preterm (EP; <28 weeks' gestation) or extremely low birth weight (ELBW; <1000 g birth weight) in the post-surfactant era (since the early 1990s) is unclear. This study investigated their bone structure and estimated bone strength using peripheral quantitative computed tomography (pQCT)-based finite element modelling (pQCT-FEM). Results using this technique have been associated with bone fragility in several clinical settings. Participants comprised 161 EP/ELBW survivors (46.0% male) and 122 contemporaneous term-born (44.3% male), normal birthweight controls born in Victoria, Australia, during 1991-92. At age 25 years, participants underwent pQCT at 4% and 66% of tibia and radius length which was analysed using pQCT-FEM. Groups were compared using linear regression and adjusted for height and weight. An interaction term between group and sex was added to assess group differences between sexes. Parameters measured included compressive stiffness (k comp ), torsional stiffness (k torsion ), and bending stiffness (k bend ). EP/ELBW survivors were shorter than the controls while their weights were similar. Several unadjusted tibial pQCT-FEM parameters were lower in the EP/ELBW group. Height- and weight-adjusted k torsion at 66% tibia remained lower in EP/ELBW (mean difference (95% confidence interval) -180 (-352,-8) Nm/deg). The evidence for group differences in k torsion and k bend at 66% tibia was stronger among males than females (p interactions <0.05). There was little evidence for group differences in adjusted radial models. Lower height- and weight-adjusted pQCT-FEM measures in EP/ELBW compared with controls suggest a clinically-relevant increase in predicted long-term fracture risk in EP/ELBW survivors, particularly males. Future pQCT-FEM studies should utilise the tibial pQCT images due to the greater variability in the radius possibly related to lower measurement precision. This article is protected by copyright. All rights reserved.