# Association Between Foot Morphology and Hallux Valgus Angle During Rotational Motion

## TL;DR

This study explores how foot shape changes during rotational motion and how these changes affect the hallux valgus angle, which could help in designing better treatments.

## Contribution

The study identifies specific foot shape factors associated with hallux valgus angle changes during rotational motion.

## Key findings

- On the rotational side, higher forefoot height and varus displacement of the digitus minimus were linked to a more varus hallux angle.
- On the non-rotational side, lower navicular height and valgus displacement of the digitus minimus were associated with a more valgus hallux angle.
- Foot shape changes during rotation are influenced by the kinetic chain and weight-bearing position.

## Abstract

Background:The foot changes shape in response to rotational motion; however, the specific nature of these changes and their relationship to hallux valgus remain unclear. In this study, we aimed to examine the relationship between foot shape alterations due to rotational motion and the hallux valgus angle.

Methods:Foot shape in healthy adult participants was measured using a three-dimensional (3D) foot scanner. Differences in foot morphology due to rotational motion were analyzed using Dunnett’s multiple comparisons method. Additionally, multiple regression analysis was conducted to identify foot shape factors associated with changes in the hallux angle.

Results:On the rotational side, the foot arch was higher, and the hallux angle tended toward varus. In contrast, on the non-rotational side, the arch was lower, and the hallux angle tended toward valgus. The forefoot, midfoot, and medial-lateral malleolus inclination angles showed angular patterns that opposed changes in the calcaneus inclination angle. Multiple regression analysis revealed that, on the rotational side, higher forefoot height and varus displacement of the digitus minimus were associated with a more varus displacement of the hallux angle. On the non-rotational side, a lower navicular height, valgus displacement of the digitus minimus, lower forefoot height, and an everted midfoot inclination angle were associated with a more valgus displacement of the hallux angle.

Conclusion:Foot shape changes induced by rotational motion are influenced by the kinetic chain and weight-bearing position resulting from lower leg rotation. The hallux valgus angle appears to be modulated by both forefoot transverse height and medial longitudinal arch function. These findings may inform targeted interventions such as exercise therapy and custom insole design.

Clinical relevance: This study suggests that insoles providing support to the forefoot transverse and medial longitudinal arches may help mitigate hallux valgus progression by reducing mechanical stress on the hallux.