Foot bone structure and plantar soft tissue deformation behavior in different functional positions

Although the static structure of the foot arch has been extensively investigated, limited information exists on the deformation of arch bones and plantar soft tissue during gait. This study aimed to evaluate the dynamic changes in foot bones and plantar soft tissues at three key gait phases (non-weight-bearing, weight-bearing, and tiptoe positions) and to analyze sagittal plane arch motion.

Sixty-seven participants underwent three-dimensional (3D) plantar scans and X-ray imaging in the three key positions. Radiographic measurements included the talo-first metatarsal angle, calcaneal pitch angle, medial arch angle, lateral arch angle, calcaneus-fifth metatarsal angle, anterior arch angle, and posterior arch angle. The arch index and arch volume were derived from a 3D foot model.

Significant differences were observed in radiographic angles and morphological parameters across positions (P<0.001). The calcaneal pitch angle and medial arch angle demonstrated the most notable changes, with arch volume increasing by 48.71% at the tiptoe position compared to weight-bearing. Participants were grouped by arch flexibility (flexible, neutral, and stiff), and the difference in changes in the medial arch angle, anterior arch angle and posterior arch angle in the flexible and stiff groups were significant (P<0.05). The change in the non-weight-bearing versus weight-bearing position in the flexible group was approximately 1.98 times greater than that in the stiff group.

The arch changes during gait are complex. At the end of the support phase, the windlass mechanism drives arch reconstruction, while arch flexibility at this stage does not affect the arch reconstruction. However, differences in arch flexibility can directly lead to changes in arch buffering patterns during weight-bearing conditions. These findings advance the understanding of foot biomechanics and offer insights into foot function assessment, orthotic design, and therapeutic strategies.