The mechanism of force transference in feet of children ages two to six

Highlights

• An algorithm was designed to quantify the plantar force transferences of toddlers;.

• Intra-, inter- and across-level force transferences were calculated within ages;.

• Both transverse and longitudinal arches had developed at an early stage of toddlerhood;.

• Arches are an important attractor engaged in the windlass mechanism while walking.

Abstract

The aim of this study was to design an algorithm to quantify the plantar force transference of children from ages 2–6. In total, 319 healthy children without abnormal gait patterns, foot deformities or injuries, able to walk independently, and with normal BMIs were recruited, and their plantar force distributions were measured. Their plantar areas were divided into ten parts: the hallux, toes #2–5, the first to fifth metatarsal heads (1st–5th MTH), the mid-foot (MF), medial heel (MH) and lateral heel (LH), in which a relative force-time integral (FTIrel) (%) was calculated. Our results show that the FTIrel was significantly transferred along either the transverse or longitudinal arches. The middle of the forefoot and the toe areas were the two main loading regions in children aged 2–3, and posterior to anterior FTIrel shifting was typical. However, anterior to posterior and lateral to medial FTI transferences were found in children aged 5–6, and major loading was found in the heel area. Further, loading in the mid-foot varied with the child's development and was observed to tend to decrease over time. Overall, according to the algorithm designed in this study, these results demonstrated that the development of the arches, both in transverse and longitudinal directions, had already begun in early stages of toddlerhood. Meanwhile, the arches were an important attractor engaged in the windlass mechanism while walking, and they played a major role as bridges to promote posterior to anterior and medial to lateral force transference.

Introduction

Infants develop rapidly, both in structure and function, particularly from the period of independent walking up until age six. During this stage, their feet experienced dynamic and progressive changes: one is the ossification of their bones and the other is the appearance of the arch structure. Arches act as link between the fore and hind foot, as well as between the medial and lateral forefoot, but also function as a cushion that ensures the safe loading of one’s feet [1]. Therefore, exploring the role of foot arches in cushioning and load transference in walking could be beneficial for better comprehension of children’s development in motion.

In early independent walking, Bosch et al. [2], [3] found a decrease in the relative maximum force under the mid-foot. Hallemans [4], [5] indicated that a clear heel roll-over gait pattern had already developed in young toddlers who were in their first 5 months of independent walking. In studies of further development, Alvarez et al. [6] and Hennig et al. [7] reported that adult-like loading patterns of young children were found after the age of 6. Meanwhile, the windlass mechanism emerges while the foot arches are developing.

With the help of the windlass mechanism, in the terminal stance phase, the longitudinal arch is lifted to produce a rigid lever [8], ensuring the foot is stable at push-off. Vereecke suggested that the flattening of the arch and stretching of the plantar aponeurosis during walking lowers the total energy cost [9]. Hence, a properly activated windlass mechanism gives a child the stability they need to effectively walkand also produces force transferences in the anterior-posterior and media-lateral directions. In terms of quantitatively assessing the plantar transfer, Bus et al. [10] designed a plantar pressure transference algorithm, based on which the effectiveness of insoles in relieving pressure was evaluated in diabetic patients; however, a similar approach has not been applied in the child population. Presently, most current studies focused on the distribution of plantar pressure of children, and its correlations within the plantar areas were not usually considered.

Therefore, the aim of this study was to design an algorithm to quantify the plantar force transference in children from ages 2–6. One hypothesis was proposed: since the roll-over gait pattern already appears in the short period of the first weeks of independent walking, the arches would play a key role in the roll-over process, as well as supporting or transferring loads in anterior-posterior and media-lateral directions.