Pathways of load transfer in custom accommodative insoles for people with diabetes

Background

Custom accommodative insoles help reduce plantar pressures in people with diabetes who are at risk of developing foot ulcers. We have developed 3D printed custom accommodative insoles with patient-specific geometry and material properties that improve offloading performance compared to traditional insoles. While effective at offloading forefoot pressure, their load redistribution mechanisms across the full foot remain unclear. The purpose of this study is to compare the load redistribution mechanisms and pathways across nine plantar regions between standard and 3D printed insoles using a load transfer algorithm.

Methods

Twenty-six feet from 17 individuals with diabetes and high forefoot plantar pressure were included. Each participant received three pairs of custom accommodative insoles: standard of care, finite element optimized 3D printed, and pressure-based 3D printed. Peak plantar pressure and force-time-integral were recorded during walking, and a load transfer algorithm was used to map redistribution.

Findings

The main pathway of load transfer across all insoles was from the metatarsal heads to the midfoot, particularly from the first metatarsal head to the medial midfoot. The finite element optimized 3D printed custom accommodative insoles had the largest load transfers away from the metatarsal heads compared to the other insole conditions.

Interpretation

Design elements like arch height, metatarsal bars, and offloading zones influenced load transfer pathways. These results underscore the potential of custom accommodative insole designs to offload high-risk areas and adds an additional perspective to quantify insole performance, though subject-specific variability remains an important factor.