Kinematic analysis of ankle stiffness in subjects with and without flat foot

•The subjects with flat foot demonstrated increased ankle stiffness during dorsiflexion.•This ankle stiffness difference was regardless of demographic factors.•Future studies needed for kinematic analysis and joint stiffness.

BackgroundAlthough the magnitude of ankle motion is influenced by joint congruence and ligament elasticity, there is a lack of understanding on ankle stiffness between subjects with and without flat foot.ObjectiveThis study investigated a quantified ankle stiffness difference between subjects with and without flat foot.MethodsThere were forty-five age- and gender-matched subjects who participated in the study. Each subject was seated upright with the tested foot held firmly onto a footplate that was attached to a torque sensor by the joint-driving device.ResultsThe flat foot group (mean ± standard deviation) demonstrated increased stiffness during ankle dorsiflexion (0.37 ± 0.16 for flat foot group, 0.28 ± 0.10 for control group; t = −2.11, p = 0.04). However, there was no significant group difference during plantar flexion (0.35 ± 0.15 for flat foot group, 0.33 ± 0.07 for control group; t = 0.64, p = 0.06).ConclusionThe results of this study indicated that the flat foot group demonstrated increased ankle stiffness during dorsiflexion regardless of demographic factors. This study highlights the need for kinematic analyses and joint stiffness measures during ankle dorsiflexion in subjects with flat foot.