The Influence of Prefabricated Foot Orthosis Use on the Modification of Foot Posture in Adults with Pronated Feet: A Randomised Controlled Trial

<b>Background:</b> The use of foot orthoses to treat different pathologies in pronated feet in adults is widespread among podiatric professionals, although it has not been conclusively demonstrated to modify foot posture in the short or medium term. <b>Objective:</b> The aim of this study was to evaluate whether prefabricated foot supports reduce pronated foot posture in adults, as measured by the foot posture index (FPI). <b>Methods:</b> A randomised controlled clinical trial was conducted in 109 subjects with pronated feet. The participants were randomly placed into a control group that did not receive any intervention and an experimental group that used prefabricated orthoses for 6 months. The changes in the FPI were evaluated in both groups at 6 months. <b>Results:</b> Over the six-month follow-up period, the delta FPI variable was changed by -1.1 ± 2.2 points in the experimental group, whereas the same variable was reduced by 1.2 ± 2.1 points in the control group (<i>p</i> = 0.001). The participants in the experimental group neutralised their FPIs significantly more than those in the control group did (39.3% vs. 8.5%; <i>p</i> = 0.041). Moreover, individuals in the experimental group were more likely to migrate from highly pronated feet to pronated feet than those in the control group were (45.8% vs. 20%; <i>p</i> < 0.001). Finally, multivariate analysis indicated that prefabricated foot orthoses were associated with an improved FPI (OR: 6.23, CI%95: 2.72-17.09; <i>p</i> < 0.001). However, the corrective effect provided by the prefabricated foot orthoses, which neutralised the pronated posture, was nullified by the presence of index minus metatarsal formula. <b>Conclusions:</b> The use of prefabricated orthoses resulted in a decreased FPI in adults, especially in those with highly pronated feet. However, the index minus presence nullified the effect of prefabricated orthoses on foot posture neutralisation.