Pregnancy-related transverse arch deformation: a subject-specific finite element analysis of the contributions of body weight and tissue stiffness

Pregnancy is accompanied by physiological changes that alter foot structure and loading conditions, which may contribute to foot pain, instability, and an increased risk of falls. Gestational weight gain and pregnancy-related changes in passive soft-tissue compliance occur simultaneously, making it difficult for clinical studies to distinguish their individual contributions to transverse arch deformation. The purpose of this study was to independently quantify the effects of increased body weight and reduced soft tissue stiffness on transverse foot arch geometry during pregnancy and to clarify their potential mechanical relevance.

A computed tomography (CT) -based subject-specific finite element (FE) model and a full factorial design were used to independently quantify the effects of body weight (W) and tissue stiffness (K) on the transverse arch. The reference-condition FE prediction was benchmarked against in-shoe plantar pressure measurements from the same participant, showing close agreement for forefoot and heel peak pressures (< 3% difference). A 4 × 4 factorial analysis was then performed across sixteen conditions, including the reference condition and the 1st, 2nd, and 3rd trimester pregnancy states.

Under the prescribed W–K schedule, the greatest model-predicted flattening occurred in the second trimester, corresponding to the stage with the largest prescribed reduction in tissue stiffness. Regression analysis showed that increased load was the primary driver of transverse widening of the midfoot, whereas modelled reductions in passive tissue stiffness predominantly governed loss of arch height and curvature. Interaction effects between load and tissue stiffness were minimal, indicating largely independent mechanical pathways. Model-predicted stresses in the medial cuneiform, intermediate cuneiform, and cuboid were highest in the second trimester.

Within this single-subject static FE framework, gestational weight gain (W) and modelled reductions in passive tissue stiffness (K) influenced the tarsal transverse arch through distinct mechanical pathways. Increased W was more strongly associated with transverse widening, whereas lower modelled K was more closely related to vertical flattening and loss of arch curvature. Among the simulated conditions, the most pronounced model-predicted flattening occurred in the second trimester, consistent with the prescribed second-trimester minimum in K. These findings provide a mechanical interpretation of pregnancy-related transverse arch deformation and may help guide future studies of supportive exercise and footwear strategies.

Not applicable.