The tarsal bones articulate with each other and demonstrate complicated kinematic characteristics. The in vivo motions of these tarsal joints during normal gait are still unclear. Seven healthy subjects were recruited and fourteen feet in total were tested in current study. Three dimensional models of the tarsal bones were first created using CT scanning. Corresponding local 3D coordinate systems of each tarsal bone was subsequently established for 6DOF motion decompositions. The fluoroscopy system captured the lateral fluoroscopic images of the targeted tarsal region whilst the subject was walking. Seven key pose images during the stance phase were selected and 3D to 2D bone model registrations were performed on each image to determine joint positions. The 6DOF motions of each tarsal joint during gait were then obtained by connecting these positions together. The TNJ (talo-navicular joint) exhibited the largest ROMs (range of motion) on all rotational directions with 7.39 ? 2.75?of dorsi/plantarflexion, 21.12 ? 4.68?of inversion/eversion, and 16.11 ? 4.44?of internal/external rotation. From heel strike to midstance, the TNJ, STJ (subtalar joint), and CCJ (calcaneao-cuboid joint) were associated with 5.97?, 5.04?, and 3.93?of dorsiflexion; 15.46?, 8.21?, and 5.82?of eversion; and 9.75?, 7.6?, and 4.99?of external rotation, respectively. Likewise, from midstance to heel off, the TNJ, STJ, and CCJ were associated with 6.39, 6.19?, and 4.47?of plantarflexion; 18.57?, 11.86?, and 6.32?of inversion and 13.95?, 9.66?, and 7.58?of internal rotation, respectively. In conclusion, among the tarsal joints, the TNJ exhibited the greatest rotational mobility. Synchronous and homodromous rotational motions were detected for TNJ, STJ, and CCJ during the stance phase.
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