Quantifying lower limb inter-joint coordination and coordination variability after four-month wearing arch support foot orthoses in children with flexible flat feet.

Introduction: Flat feet in children negatively affect lower limb alignment and cause adverse health-related problems. The long-term application of foot orthoses (FOs) may have the potential to improve lower limb coordination and its variability.

Aim: To evaluate the effects of long-term use of arch support FOs on inter-joint coordination and coordination variability in children with flexible flat feet.

Methods: Thirty boys with flexible flat feet were randomly assigned to the experimental (EG) and control groups. The EG used medial arch support FOs during daily activities over a four-month period while the control group received a flat 2-mm-thick insole for the same time period. Lower-limb coordination and variability during the 3 sub-stance phases were quantified using a vector coding technique.

Results: Frontal plane ankle-hip coordination in EG during mid-stance changed to an anti-phase pattern (156.9) in the post-test compared to an in-phase (221.1) in the pre-test of EG and post-test of CG (222.7). Frontal plane knee-hip coordination in EG during loading response (LR) changed to an anti-phase pattern (116) in the post-test compared to an in-phase (35.5) in the pre-test of EG and post-test of CG (35.3). Ankle inversion/eversion-knee internal/external rotation joint coupling angle in EG changed to an in-phase pattern (59) in the post-test compared to a proximal phase (89) in the pre-test. Coupling angle variability increased in the post-test of EG for sagittal plane ankle-hip during push-off, transverse plane ankle-hip during LR and mid-stance, and transverse plane knee-hip during LR and mid-stance compared to pre-test of EG and post-test of CG.

Conclusion: The long-term use of arch support FOs proved to be effective to alter lower limb coordination and coordination variability during walking in children with flexible flat feet. This new insight into coordinative function may be useful for improving corrective exercise strategies planned for children with flat feet.