Novel shoe inserts for adult-acquired flatfoot deformity—design, fabrication, and biomechanical assessment

Flatfoot is a condition where the curve of medial longitudinal arch is missing, and excessive subtalar joint eversion is observed while standing and walking. The abnormal foot structure compromises foot motion and increases risk of injury and musculoskeletal symptoms. Flatfoot may potentially progress to a more severe foot deformity if no preventive action is taken. Corrective shoe insert is the most common intervention for flatfoot, which have been shown to increase the arch height and reduce the excessive joint¿s motion. However, current shoe insert uses full arch support made by solid filling that can restrict the dynamic response of the foot arch and compromise the natural foot motion in gait. This can result in reducing the elastic energy return and decreasing the movement efficiency. In current study, the novel inserts with elastic mesh pad are developed to address the current limitations of flatfoot shoe insole. A fully automated process including 3D scanning, computer-aided design, and addictive manufacturing was used for novel insert customization. Through our motion analysis, the novel inserts showed to facilitate the dynamic response of the foot arch and increase the midfoot motion (i.e. arch compression and recoil) in gait. Additionally, the tissue and joint stress of the foot are reduced by the novel inserts and increases the comfort level of the users. In current study, a foot arch assessment system through subject-specific 3D foot model reconstruction has been also developed, which successfully reduces the misclassification rate between low and normal arch from 55%, as reported by previous study, to 6.9%. Moreover, a parametric insert design method is developed to automatically transferred the 3D scanned data to customized insert geometry, which reduced the required time of customized insert design from 3 hours to 3 minutes.