Effect of Flatfoot on Rearfoot Eversion Moment During the Support Phase of Walking
Excessive eversion of the talus and calcaneus (i.e., the rearfoot) during the support phase of walking occurs as a result of excessive moments about the ankle caused by ground reaction forces (GRF) and may eventually lead to chronic lower limb injuries. In this study, I investigated whether individuals with flatfoot are susceptible to excessive rearfoot eversion during walking. Healthy adult male participants (n = 29) were divided, by normalized truncated navicular height, into 2 groups—individuals with flatfoot (n = 14, low values) and individuals with normal foot characteristics (n = 14, high values; the participant with the median value was excluded). Rearfoot eversion moments and the factors generating moments (ankle height, mediolateral GRF, mediolateral distance of COP, mediolateral distance of center of the ankle, vertical GRF) were calculated. These variables were compared between groups. Participants with flatfoot had significantly larger eversion moments than those in the control group after foot contact and during the loading phase; ankle joint centers in participants with flatfoot were located significantly medial to those of participants in the control group, and as a result, the mediolateral distance between the COP and the ankle (the eversion moment arm of vertical GRF) was significantly larger. Because individuals with flatfoot have ankle joint centers located medial to those with normal foot characteristics during the support phase of walking, and consequently, have an increased mediolateral distance between COP and the center of the ankle, individuals with flatfoot are susceptible to large rearfoot eversion moments.