The Long-Term Wearing of Foot Orthoses Can Change the Frequency Domain of Ground Reaction Forces in Children with Flexible Flat Feet

ABSTRACT Introduction Analyzing the frequency content of ground reaction forces (GRFs) might be helpful when assessing gait abnormalities in children with flexible flatfeet. The aims of this study were therefore to evaluate 1) differences in GRF frequency content between children with and without flatfeet; and 2) whether the long-term wearing of foot orthoses changes the GRF frequency contents in children with flatfeet. Materials and Methods This is a pre-post study design. GRFs were collected at baseline for boys both with and without flatfeet. Boys with flatfeet wore custom-made foot orthoses with unique shoes for 4 months; GRFs were collected for the flatfeet group after 4 months too. Data were collected while participants wore shoes without foot orthoses in the pretest and shoes with foot orthoses in the posttest. GRFs were collected during walking by two Kistler force platforms (each force plate was used for each leg). Multivariate analysis of variance (MANOVA) test and a separate 2 (side: dominant vs. nondominant) × 2 (time: pretest vs. posttest) ANOVA with repeated measures were used for statistical analysis. Results The flatfeet group indicated lower vertical GRF frequency (P = 0.003; d = 1.21; 95% confidence interval [CI], 7.12–7.59) and greater vertical amplitude of harmonic 16 for the nondominant limb (P = 0.030; d = 0.71; 95% CI, 0.0001–0.0022) than the normal feet group. No significant differences in GRF frequency content were found for the dominant limb between pretest and posttest (P > 0.05; d = 0.01–039). However, for nondominant limb, vertical GRF frequency content (P < 0.001; d = 0.85; 95% CI, 6.21–7.36) was diminished at posttest compared with pretest. In the nondominant limb, the anteroposterior GRF frequency with a power of 99.5% showed a significant increase at posttest compared with pretest (P = 0.025; d = 0.50; 95% CI, 13.30–16.20). For both limbs, amplitudes of three-dimensional GRF components were lower at posttest than at pretest (P < 0.05; d = 0.0.14–1.20; 95% CI, −0.0005 to −0.0083). Conclusions The results indicated lower GRF frequency content and amplitudes after long-term wearing of foot orthoses. Therefore, long-term wearing of foot orthoses may be applied to obtain functional improvements in children with flatfeet. Clinical Relevance Clinicians are advised to apply foot orthoses to improve functions in children with flatfeet.