The effect of the subtalar orientations on the plantar foot geometry

Abstract

Foot alignment control is regarded as one of the most important elements in the impression procedure in foot orthosis. Keeping the subtalar joint in its neutral position by palpating the joint congruity and keeping the plane of the forefoot parallel to the plane of the heel are recommended. However, results of gait analyses showed that the subtalar joint is in an everted position for over 60% of the stance phase in normal walking. The rationale of keeping the subtalar joint in a neutral position during the foot impression procedure is questionable. This study aimed at investigating the effect of the subtalar orientations on the plantar foot geometry three-dimensionally. Twenty adults with normal foot type participated in this study. Bilateral foot impressions were taken with the subtalar joint angles ranging from 2o inversion to 4o eversion. The plane of the forefoot at the metatarsal heads region was kept perpendicular to the calcaneal bisection line. Positive plaster models were generated from these impressions and scanned with a three dimensional laser imaging system. Custom computer software was designed to quantify the plantar foot geometry in terms of foot parameters such as projection volumes at different foot regions, medial-lateral cross-section slopes, arch heights, and etc. It was observed that the projection volume and the medial-lateral slopes of the medial longitudinal arch were the lowest at 2o eversion. On the other hand, the projection volume under the medial forefoot region became the highest at 4o eversion. Although these were significant differences found in the projection volume under the medial midfoot regions among various subtalar joint orientations, the changes in the arch heights were 0.1- 0.6 mm (p = 0.05). This implied that the changes were concentrated at the soft tissue margin medial to the medial longitudinal arch. Thus it is suggested that the subtalar neutral position during foot impression procedure should not be over emphasized. Investigation on the effect of the forefoot alignment control on the plantar geometry is recommended in further studies.