Bone Abstracts

Hip development is influenced by mechanical loading during fetal movement by joint and reaction forces equivalent to several times bodyweight. These forces increase with fetal size and gestation length, and are lower in oligohydramnios and breech presentation which are both risk factors for developmental hip disorders. However, associations between indicators of prenatal mechanical loading and hip shape in later life remain unexplored. We therefore examined associations between prenatal loading indicators (birthweight, gestation length, oligohydramnios, polyhydramnios and presentation at birth) and hip shape in late adolescence in 2004 participants (1086 female) from the Avon Longitudinal Study of Parents and Children (ALSPAC). Prenatal indicators were obtained from obstetric records, and hip shape was quantified using dual-energy X-ray absorptiometry (DXA) images taken at age 17 years from which hip shape modes (HSMs) were generated. Associations were examined in models adjusted for sex, and potential confounders (maternal education, maternal smoking, parity, maternal age). 21 participants had oligohydramnios, 19 had polyhydramnios and 103 had breech presentation. Birthweight was positively associated with HSM1, and negatively associated with HSM2 and HSM5, whilst gestation length was positively associated with HSM4 and HSM5. There was little evidence of associations between polyhydramnios or breech presentation and hip shape. In contrast, oligohydramnios was associated with substantially lower HSM1 scores in males (−1.14 S.D., 95%CI −1.82S.D. to −0.45S.D.) but not females (0.08S.D., −0.47 to 0.63 S.D., sex interaction P=0.006). Oligohydramnios was also associated with lower HSM7 scores in both sexes (−0.43S.D., −0.86 to −0.01S.D., sex interaction P=0.788), and with greater HSM8 scores in males (1.05S.D., 0.38 to 1.71S.D.) but not females (0.23S.D., −0.33 to 0.78S.D., sex interaction P=0.063). In males with prenatal oligohydramnios, the shape described by these HSM differences was characterised by narrower upper femur width, and differences in greater and lesser trochanter size and shape. Further adjustment for potential mediators (delivery method, and height, fat mass and lean mass at 17 years) did not affect results. These results suggest that prenatal skeletal loading may influence joint shape in adolescent males. In particular, oligohydramnios is associated with large differences in hip shape, although small sample size means replication is required.

Disclosure: The authors declared no competing interests.