Pathological kinematic patterns of the tarsal complex in stage II adult-acquired flatfoot deformity.

The in vivo kinematic characteristics of the tarsal joints during gait stance phase were still unclear in adult-acquired foot deformity (AAFD). This study included seven healthy subjects (14 feet) and 12 stage II AAFD patients (14 feet). The 3D models of tarsal bones were reconstructed based on CT scan. Each subject took standard gait on the single fluoroscopy system. Continuous lateral fluoroscopic images were collected. The key postures during the stance phase were selected. The 2D-3D registration technique was applied to explore the spatial motions of the tarsal joints in 6 degrees of freedom (DOF). During the whole stance phase, the AAFD talo-navicular joint (TNJ) exhibited ROM of 13 ± 6° in the sagittal plane while the normal subjects showed ROM of 7 ± 3° (p = 0.004). In AAFD, the subtalar joint (STJ) demonstrated 19 ± 8° and 7 ± 3° of motion in coronal and horizontal plane, respectively, while the normal subjects showed 14 ± 4°(p = 0.031) and 11 ± 3° (p = 0.014) of motion, respectively. Additionally STJ of AAFD patients showed significantly less dorsiflexion during the weight acceptance and showed significantly less external rotation both during the weight acceptance and single limb support of stance phase. In conclusion, for stage II AAFD patients, the talonavicular joint and the subtalar joint showed hypermobility in dorsi/planterflexion and inversion/eversion, respectively, during the gait stance phase while the internal/external rotation of the subtalar joint was reduced. The current study improves our understanding of the pathological kinematics of the tarsal complex in AAFD patients. Notice should be taken about these tarsal joints mobility in AAFD during clinical practice.