The influence of foot orthoses on foot mobility magnitude and arch height index in adults with flexible flat feet

Background: Flexible flat foot is described as a reduction in the height of the medial longitudinal arch and may occur from abnormal foot pronation. A foot orthosis is thought to modify and control excessive pronation and improve arch height. Objective: To compare the immediate effect of three types of orthoses on foot mobility and the arch height index in subjects with flexible flat feet. Study design: A quasi-experimental study. Method: The dorsal arch height, midfoot width, foot mobility and arch height index were assessed in 20 participants with flexible flat feet (mean age = 23.2 3 years) for three different foot orthosis conditions: soft, semi-rigid and rigid University of California Biomechanics Laboratory (UCBL). Results: Maximum midfoot width at 90% with arch mobility in the coronal plane was shown in the semi-rigid orthosis condition. The semi-rigid orthosis resulted in the highest mean foot mobility in 90% of weight bearing, and the rigid orthosis (UCBL) had the lowest mean foot mobility. The soft orthosis resulted in foot mobility between that of the rigid and the semi-rigid orthosis. UCBL orthosis showed the highest arch height index, and the semi-rigid orthosis showed the lowest mean arch height index. Conclusion: Due to its rigid structure and long medial-lateral walls, the UCBL orthosis appears to limit foot mobility. Therefore, it is necessary to make an orthosis that facilitates foot mobility in the normal range of the foot arch. Future studies should address the dynamic mobility of the foot with using various types of foot orthoses. Clinical relevance Although there are many studies focussed on flat foot and the use of foot orthoses, the mechanism of action is still unclear. This study explored foot mobility and the influence of foot orthoses and showed that a more rigid foot orthosis should be selected based on foot mobility.