A thorough understanding of the influence of the foot skeletal structure on hallux valgus (HV) is required for HV prevention. We developed a system using a 3D foot scanner on a smartphone to clarify the relationships between foot features and HV risk. Two-dimensional video images were recorded on a smartphone, sent to a computer or cloud server, and used to construct a 3D foot-feature model, considering 10 foot features associated with HV. The participants (419 individuals, aged 40-89 years) stood with their toes 12 cm apart and heels 8 cm apart during video recording. The height and weight were measured for body-mass index calculation. Age-dependent foot-feature variations were observed slightly for males and distinctively for females. For females, the great toe-first metatarsal head-heel (GFH) angle associated with HV increased with age, i.e., the GFH angle increased with age, suggesting that HV increased with age. Multiple regression analysis revealed that the features determining the GFH angle are the second toe-heel-navicular angle, bone distance axis, and transverse arch length and height. The adjusted coefficients of determination were 0.54 and 0.52 for males and females, respectively. This approach enables simple foot structure assessment for HV risk evaluation.

Abnormalities in the feet and toenails are common among the elderly and may increase the risk of falls. This study aimed to investigate the changes in toe-gap force, knee-gap force, foot pressure distribution, the ability to perform activities of daily living, subjects’ feelings and behaviors, and physical function resulting from daily lifestyle modification and foot care. The study participants included 74 elderly adults (mean age 80.3 ± 7.5 years) with foot problems who had been divided into three groups based on Japan’s nursing care insurance system levels: certified ineligible for support, eligible for support, or eligible for long-term care. Additionally, a control group of 106 elderly adults in good health was recruited. The differences between the intervention and control groups was examined using the Student’s t-test, and differences between the three intervention subgroups and the control group were examined using one-way analysis of variance. After intervention, abnormalities in the participants’ feet and toenails improved. Significant increases in lower-limb muscle strength were observed, and foot pressure distribution had improved. The foot-care intervention significantly improved lower-limb muscle strength and decreased the risk of falling, even in elderly adults whose physical function had deteriorated. In frail elderly adults, care of the feet and toenails can improve lower-limb muscle strength and foot pressure distribution. In addition, the individuals’ social participation increased, and their behavior improved. University hospital Medical Information Network- Clinical Trials (UMIN-CTR) with the number: UMIN000034742 . Registration date: 11/01/2018.

Frailty in older adults often leads to foot issues, increasing fall-related fracture risk. Mechanoreceptors, the pressure receptors in the foot sole, are pivotal for postural control. Foot problems can impair mechanoreceptor function, compromising balance. This study aimed to examine the effect of foot care on postural control in frail older adults. Forty-eight participants underwent a five-month monthly foot care intervention. Measurements were taken before and after this intervention. Participants stood for 45 s in a static, open-eyed position on a stabilometer. Center-of-pressure (CoP) analysis included total trajectory length, integrated triangle area, rectangular area, and range of motion in anterior-posterior and medio-lateral directions. Results indicated that foot care significantly increased toe ground contact area by 1.3 times and improved anterior-posterior motion control during static standing. Enhanced postural control resulted from improved skin condition due to foot care that intensified mechanoreceptor signal input and improved postural control output. These findings underscore the potential for reducing fracture risks in older adults through proactive foot care. The study highlights the vital role of foot care in enhancing postural control, with broader implications for aging population well-being and safety.

The structures around the navicular bones, which constitute the medial longitudinal arch, develop by 10 years of age. While navicular bone height is often emphasized in the assessment of flatfoot, three-dimensional (3D) evaluations, including those of structural parameters during inversion, have rarely been investigated. If the development of flatfoot during the growth process could be predicted, appropriate interventions could be implemented. Therefore, in this longitudinal cohort study, we developed a system, utilizing smartphones, to measure the 3D structure of the foot, performed a longitudinal analysis of changes in midfoot structures in 124 children aged 9–12 years, and identified factors influencing the height of the navicular bone. The foot skeletal structure was measured using a 3D system. Over 2 years, foot length and instep height increased during development, while navicular height decreased. The 25th percentile of the instep height ratio and navicular height ratio at ages 9–10 years did not exceed those at ages 11–12 years, with percentages of 17.9% and 71.6%, respectively, for boys, and 15.8% and 49.1%, respectively, for girls. As the quartiles of the second toe–heel–navicular angle (SHN angle) increased at ages 9–10 years, the axis of the bone distance (ABD) and SHN angles at ages 11–12 years also increased, resulting in a decrease in the navicular height ratio. A significant inverse correlation was found between changes in SHN angle and navicular height ratio. These findings indicate that the navicular bone rotation of the midfoot is a predictor of the descent of the navicular bone. This study revealed that some children exhibit decreases in navicular bone height with growth. As a distinct feature, the inversion of the navicular bone promotes flattening of the midfoot. Thus, this study provides insights into changes in midfoot development in children and provides an effective evaluation index.