Age at Onset ofWalking in Infancy Is AssociatedWith Hip Shape in Early

Bones’ shapesandstructuresadapt to themuscleand reaction forces theyexperienceduringeverydaymovements.Onsetof independent walking, at approximately 12months, represents thefirst postnatal exposure of the lower limbs to the large forces associatedwithbipedal movements; accordingly, earlier walking is associated with greater bone strength. However, associations between early life loading and joint shapehavenotbeenexplored.We thereforeexaminedassociationsbetweenwalkingageandhip shapeat age60 to64years in 1423 individuals (740 women) from the MRC National Survey of Health and Development, a nationally representative British birth cohort. Walking age in months was obtained from maternal interview at age 2 years. Ten modes of variation in hip shape (HM1 to HM10), described by statistical shape models, were ascertained from DXA images. In sex-adjusted analyses, earlier walking age was associated with higher HM1 and HM7 scores; these associations were maintained after further adjustment for height, body composition, and socioeconomic position. Earlier walking was also associated with lower HM2 scores in women only, and lower HM4 scores in men only. Taken together, this suggests that earlier walkers have proportionately larger (HM4) and flatter (HM1, HM4) femoral heads, wider (HM1, HM4,HM7) andflatter (HM1,HM7) femoral necks, a smaller neck-shaft angle (HM1,HM4), anteversion (HM2,HM7), andearly development of osteophytes (HM1). These results suggest that age at onset of walking in infancy is associatedwith variations in hip shape in older age. Early walkers have a larger femoral head and neck and smaller neck-shaft angle; these features are associated with reduced hip fracture risk, but also represent an osteoarthritic-like phenotype. Unlike results of previous studies of walking age and bone mass, associations in this study were not affected by adjustment for lean mass, suggesting that associations may relate directly to skeletal loading in early life when joint shape changes rapidly. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.