Effects of a foot orthosis custom-made to reinforce the lateral longitudinal arch on three-dimensional foot kinematics

摘要

There is extensive evidence of the benefits of a foot orthosis; however, it is dependent on the skill and experience of the clinician. The purpose of this study was to clarify the effects on 3D foot kinematics of a custom-made foot orthosis (CMFO) which reinforced the lateral longitudinal arch, without subjective assessments. All eighteen feet of nine normal volunteers who had a flat-foot deformity were included in this study. The CMFO was designed according to each participant's foot shape using high-density polyethylene for the medial CMFO. The lateral part of the CMFO was then designed to cover the lateral longitudinal arch using polypropylene and was made to fit the medial CMFO. The full CMFO was defined as the medial CMFO together with the lateral CMFO. Eleven reflective skin markers were mounted over the anatomical landmarks of the foot and foot motion during the forward lunge without stride were recorded using eight infrared cameras; the spatial coordinates of those markers were then calculated. Differences between the three conditions: without CMFO, with medial CMFO and with full CMFO in displacement of all markers, were then calculated during the forward lunge. Medial movements of the third metatarsal base, and the medial and posterior top of the calcaneus with the full CMFO were significantly smaller than those with the medial CMFO. Therefore, the full CMFO which reinforced the lateral longitudinal arch could cause reduced movement of the rear-foot indicated by the calcaneus during the forward lunge. Our CMFOs demonstrate that changing the stiffness of the lateral part of the CMFO could reduce rear-foot motion in the medial direction without any form change. This might help with the manufacture of an appropriate CMFO without subjective assessment.