Diaphyseal cross-sectional geometry of the metatarsal bones in the Jomon population.

OBJECTIVES: This study aimed to investigate differences in the diaphyseal cross-sectional geometry (CSG) of the metatarsal bones (MTs) between two populations with different habitual activities: the Jomon hunter-gatherers and modern Japanese people.

MATERIALS AND METHODS: We evaluated the first through fifth MTs of 117 skeleton samples: 59 (33 men and 26 women) were obtained from Late and Final Jomon period archeological sites and 58 (31 men and 27 women) were from modern Japanese people. CSG properties were calculated at the mid-shaft of the MTs and the relative values of the polar section modulus (Zp ) of each second-to-fifth MTs to first MTs were calculated. These variables were compared according to population and sex.

RESULTS: Many of the CSG properties of MTs, except first MTs, were higher in the Jomon population than in the modern Japanese population for both sexes. Additionally, the relative values of the Zp of the MTs were higher in Jomon men and women than in modern Japanese men and women. Moreover, the Jomon population had sex-based differences in the ratio of the shape of third MTs and fourth MTs and the relative MTs value. Jomon women had elliptical third MTs and fourth MTs, and the relative Zp values of the third-to-fifth MTs to first MTs were higher in Jomon women than in Jomon men.

DISCUSSION: Our result suggests that the habitual activity of the Jomon population placed heavy loads on the forefoot. This finding possibly relates to mediolateral forefoot loading that appears to be related to traversing uneven terrain.