Orthoses can stabilize the foot and restore the medial longitudinal arch for symptomatic flexible flatfoot. However, the effectiveness of orthoses remains controversial. The purpose of this study was to evaluate effectiveness of a customized soft inflatable orthosis on the medial longitudinal arch of flexible flatfoot patients under load.

We obtained CT scans of the feet of 14 healthy volunteers and 14 patients with flexible flatfoot under non- and simulated weight-bearing conditions. Then CT scans under the same conditions were taken for patients with flexible flatfoot equipped with soft inflatable orthosis. Three-dimensional models of the medial longitudinal arch and hindfoot were constructed from CT images. The three-dimensional mobility of the medial longitudinal arch joints under load was compared between patients with flexible flatfoot equipped with soft inflatable orthosis or not.

From non- to simulated weight-bearing condition, the eversion and dorsiflexion of the talocalcaneal joint, the eversion of the talonavicular joint, the abduction and dorsiflexion of the cuneonavicular joint, and the dorsiflexion of the first tarsometatarsal joint were significantly larger in patients with flexible flatfoot than healthy volunteers. The customized soft inflatable orthosis could reduce the eversion of the talonavicular joint and the eversion and dorsiflexion of the talocalcaneal joint.

The soft inflatable orthosis is effective to improve medial longitudinal arch height and reduce excessive mobility of joints for flexible flatfoot deformity. The results of this study could provide evidence for the optimal orthosis design to treat flexible flatfoot in the future.