Secular changes in the angle of divergence of the first two metatarsals in the Japanese.

Abstract

This investigation concerns secular changes of the intermetatarsal M1-M2 angle in the foot of Japanese, from the prehistoric Jomon period to early modern times. The divergence of the first metatarsal from the second in both sexes in the reconstructed tarsometatarsal bones gradually decreased during this period. In addition, the difference between sexes or sides in each period is small and statistically insignificant. With time, the first metatarsocuneiform angles, in both sexes, also decreased in parallel with the reduction of the intermetatarsal M1-M2 angle, while the second metatarsocuneiform angles in both sexes increased. Both may play a role in decrease of the intermetatarsal M1-M2 angle. A conspicuous angular divergence of the first metatarsal from the second one occurred in comparatively recent times. This change would be accelerated by modification in life-style, together with the effects of footwear.