Effects of custom-made insole on the mechanical response characteristics of the foot during static standing and walking

Custom-made insoles are designed to redistribute foot load and prevent potential pain. Common methods to investigate the effectiveness of insoles include finite element method and experimental approach. However, most finite element research has focused on the two-dimensional plantar fascia stresses during static standing with insoles, rather than those of three-dimensional plantar fascia. Furthermore, the effects of insole with design parameters (metatarsal pad, toe pad, and arch support) on dynamic plantar pressures still need further exploration. Therefore, this study aimed to quantify the impact of custom-made insoles on foot biomechanics by combining both methods. Finite element method was employed to evaluate stress on the plantar fascia and bony structures when static standing, both barefoot and with a custom-made insole. Furthermore, 10 participants were recruited to investigate dynamic plantar pressures during walking barefoot and with insole. The relative time of four subphases during stance phase, total contact time, peak plantar pressure (Peak P), and pressure time integral (PTI) were assessed. Finite element results revealed reduced plantar fascia stresses and more uniform stress distribution over metatarsals and phalanges when standing with insole. Additionally, Peak P and PTI values in the second and third metatarsals were significantly lower when walking with insole. With the presence of insole, Peak P and PTI values in medial regions were significantly reduced, except for the midfoot region. In conclusion, custom-made insole with the addition of a metatarsal pad, toe pad, and arch support can effectively distribute foot tissue stress evenly, alleviate plantar pressure, and thus prevent pain.