Objective: To determine the quantitative effects of a corrective rearfoot orthotic device on the vertical, anteroposterior, and mediolateral ground reaction forces (GRFs) during ambulation. Design: We conducted a prospective, randomized, single-blinded study of 25 subjects during ambulation with and without a rearfoot orthotic device. Material and Methods: Thirteen men and 12 women were enrolled in the study; the inclusions criteria included asymptomatic pes planus (5 to 10 degrees of calcaneal eversion). Each subject walked across a standard force plate in 10 trials with and 10 trials without an orthotic device. The force plate was used to quantify the effect of a semirigid function rearfoot orthotic device on GRFs and the center of pressure versus a standard shoe with no device. The observer was blinded, trials were completed in random order, and the paired t test was used for statistical analysis. Results: No evidence suggested the presence of a significant difference in mediolateral GRFs and in the center of pressure exerted at 10%, 20%, 50%, and 80% of stance phase with and without the orthotic device. Significant reductions were noted in vertical GRFs per newton of body weight exerted at 10% (P = 0.0009) and 20% (P = 0.0383) of stance phase and in anteroposterior GRFs exerted at 10% (P = 0.0009) and 50% (P = 0.0033) of stance phase when ambulation was compared with and without the orthotic device. Conclusion: These results indicate that a rearfoot orthotic device reduces vertical and anteroposterior GRFs in the early stages of the stance phase during the gait cycle. We found no evidence to suggest a significant difference at any of the percent stance phases when comparisons were made of mediolateral GRFs exerted with and without the orthotic device. The data are contrary to current hypotheses about use of orthotic devices, and further studies would be helpful to reproduce these findings and to determine whether these changes are related to clinical improvement in symptomatic pes planus.
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