Abnormal foot kinematics is observed in flatfoot subjects with postural foot deformity. We aimed to investigate joint instability in flatfoot subjects by analyzing the abnormal rotational position and speed of their joints while walking. Five flatfoot subjects participated in our study. Three-dimensional motions of the tibia, talus, calcaneus, navicular, and cuboid were obtained during walking using the biplanar fluoroscopic motion analyses. An anatomical coordinate system was established for each bone. The rotations and ranges of motion (ROMs) of the joints from heel-strike to toe-off were quantified. The relative movements on the articular surfaces were quantified by surface relative velocity vector analysis. The data from flat foot subjects were compared with the data from normal foot subjects in previous studies. The average relative speed on the articular surface of the tibiotalar, subtalar, and calcaneocuboid joints for the flatfoot subjects was significantly higher (p < 0.05) than that for the normal foot subjects. The flatfoot subjects exhibited increased movements toward plantar flexion in the tibiotalar joint, and eversion and external rotations in the talonavicular joint during the stance phase, compared to the normal subjects (p < 0.01). Furthermore, the flatfoot subjects had a significantly larger ROM along with the inversion/eversion rotations (5.6 ± 1.8° vs. 10.7 ± 4.0°) and internal/external rotations (7.1 ± 1.5° vs. 10.5 ± 3.5°) in the tibiotalar joint. The flatfoot subjects demonstrated abnormal kinematics and larger joint movements in multiple joints during the mid-stance and terminal stance phases of walking. This demonstrates their high instability levels.

在具有姿势性足部畸形的平足受试者中观察到异常足部运动学。我们旨在通过分析步行时关节的异常旋转位置和速度来研究平足受试者的关节不稳定性。五名扁平足受试者参与了我们的研究。使用双平面荧光透视运动分析在行走过程中获得胫骨、距骨、跟骨、舟骨和长方体的三维运动。为每个骨骼建立了解剖坐标系。量化关节从足跟触地到脚趾离地的旋转和运动范围 (ROM)。通过表面相对速度矢量分析量化关节表面上的相对运动。扁平足受试者的数据与之前研究中正常足受试者的数据进行了比较。平足受试者胫距、距下和跟骰关节关节面的平均相对速度明显高于正常足受试者（p < 0.05）。与正常受试者相比，扁平足受试者的胫距关节向跖屈运动增加，在站立期距舟关节的外翻和外旋运动增加（p < 0.01）。此外，扁平足受试者的 ROM 以及胫距关节的内翻/外翻旋转（5.6 ± 1.8° vs. 10.7 ± 4.0°）和内/外旋转（7.1 ± 1.5° vs. 10.5 ± 3.5°） . 扁平足受试者在行走的中间站立和站立末期阶段表现出异常的运动学和多个关节的较大关节运动。