Comparative radiographic analysis of three-dimensional innate mobility of the foot bones under axial loading of humans and African great apes

The human foot is considered to be morphologically adapted for habitual bipedal locomotion. However, how the mobility and mechanical interaction of the human foot with the ground under a weight-bearing condition differ from those of African great apes is not well understood. We compared three-dimensional (3D) bone kinematics of cadaver feet under axial loading of humans and African great apes using a biplanar X-ray fluoroscopy system. The calcaneus was everted and the talus and tibia were internally rotated in the human foot, but such coupling motion was much smaller in the feet of African great apes, possibly due to the difference in morphology of the foot bones and articular surfaces. This study also found that the changes in the length of the longitudinal arch were larger in the human foot than in the feet of chimpanzees and gorillas, indicating that the human foot is more deformable, possibly to allow storage and release of the elastic energy during locomotion. The coupling motion of the calcaneus and the tibia, and the larger capacity to be flattened due to axial loading observed in the human foot are possibly morphological adaptations for habitual bipedal locomotion that has evolved in the human lineage.

Automated summary

This study compared the 3D bone kinematics of cadaver feet under axial loading between humans and African great apes, finding that the human foot shows more coupling motion of certain bones and greater deformability than the feet of African great apes, possibly to accommodate for habitual bipedal locomotion. The morphological adaptations of the human foot, such as the coupling motion of the calcaneus and tibia, and the increased deformability under axial loading, suggest evolutionary changes in the human lineage for bipedal locomotion.