The effect of foot structure and custom molded functional orthotic (FO) intervention on walking kinematics was investigated using a novel multi-segment three-dimensional (3D) foot model. Eighteen participants with low and mobile arch structures (LAMF) and 11 participants with "typical" arch structure and mobility (TYPF) were recruited. The LAMF participants were randomly assigned to one of two different FOs. Following a semi-weightbearing anatomical calibration procedure, subjects completed 5 walking trials along a 10 m walkway at a speed of 3--3.15 mph. Three-dimensional data were captured using 8 optical electronic cameras sampling at 120 Hz (Peak Performance Technologies, Inc.). The LAMF group performed trials during no FO and FO conditions while the TYPF group only performed no FO condition trials. A software program written in Matlab (MathWorks) was used to compute joint angles and discrete kinematic stance phase variables. The LAMF group (no FO condition) demonstrated less rearfoot complex (RC) sagittal plane angular displacement (p = 0.012), slower time-to-peak (TTP) inversion (p = 0.043) and greater inversion velocity (p = 0.049) compared to the TYPF group. LAMF group no FO versus FO condition comparisons revealed increased RC inversion (p = 0.001) and internal rotation (p = 0.016) angles and decreased eversion (p = 0.001) angles during the FO condition. At the calcaneonavicular complex, later TTP plantarflexion angle (p = 0.001) and eversion velocity (p = 0.045) and earlier adduction angular velocity (p = 0.012) were observed during the FO condition. At the medial forefoot, decreased plantarflexion (p = 0.002) and inversion (p = 0.001) angles and sagittal plane angular displacements (p 0.001) were observed during the FO condition while eversion angles were increased (p = 0.012). Decreased plantarflexion (p = 0.004) and eversion (p = 0.003) velocities were also observed during the FO condition. Finally, decreased eversion angles (p = 0.046) and sagittal (p = 0.008) and frontal plane (p = 0.001) angular displacements were observed at the first metatarsophalangeal joint during the FO condition. The results of the study suggest significant kinematic differences do exist between subjects with "typical" foot structures and those with low and mobile arch structures. It also demonstrated that FO intervention significantly affects walking gait kinematics in persons with low and mobile arch structures.
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