["American Journal of Biological Anthropology, Volume 190, Issue 4, August 2026. ", "\nABSTRACT\n\nObjectives\nPlatycnemia, a mediolateral flattening of the tibial shaft, has been argued to be an adult phenomenon caused by mechanical forces shaping bone. Here we investigate the possibility that this condition develops prior to growth plate closure, at a time when the epiphyseal cartilage is responsive to torsional loading.\n\n\nMaterials and Methods\nWe analyze the degree of torsion along the tibial shaft and compare that to the cnemic index (a measure of platycnemia) in two populations: ancient Jomon and modern Japanese. Through linear mixed‐effects modeling, we aimed to determine whether platycnemia, as measured by the cnemic index, is correlated with the magnitude of torsion that the tibia undergoes during development, prior to growth plate closure.\n\n\nResults\nOur results show that cnemic index significantly decreases as individuals age and the tibia lengthens, resulting in increasing mediolateral flattening and greater instances of platycnemia. However, we found no significant relationship between tibial torsion and the cnemic index.\n\n\nDiscussion\nOur findings suggest that a broader range of genetic, biomechanical, and environmental properties needs to be considered when hypothesizing how skeletal modeling might be related to the development of platycnemia.\n\n"]