BackgroundFlatfoot deformity is a lever arm disease that incurs kinetic inefficiency during gait. The purpose of this study was to measure the degree of kinetic inefficiency by comparing the gait analysis data of a flatfoot group with a normal control group.MethodsThe patient group consisted of 26 children (21 males and 5 females) with symptomatic flatfoot. They were examined with gait analysis between May 2005 and February 2014. Exclusion criteria were patients with secondary flatfoot caused by neuromuscular disorders, tarsal coalition, vertical talus, or others. Patients' mean age was 9.5 years (range, 7 to 13 years). The gait analysis data of the study group and the normal control group were compared.ResultsThe mean vertical ground reaction force (GRF) in the push-off phase was 0.99 for the patient group and 1.15 for the control group (p < 0.05). The mean ankle moment in the sagittal plane during the push-off phase was 0.89 for the patient group and 1.27 for the control group (p < 0.05). The mean ankle power in the sagittal plane during the push-off phase was 1.38 for the patient group and 2.52 for the control group (p < 0.05). The aforementioned results show that patients with pes planovalgus had a reduction of moment, power, and GRF in the push-off phase during gait.ConclusionsSymptomatic flatfeet had a moment inefficiency of 30% and power inefficiency of 45% during gait compared to feet with preserved medial longitudinal arches.