Comparison of in vivo hindfoot joints motion changes during stance phase between non-flatfoot and stage II adult acquired flatfoot.

BACKGROUND

To compare the kinematic characteristics of hindfoot joints in stage II adult acquired flatfoot deformity (AAFD) with those of non-flatfoot through the 3D-to-2D registration technology and single fluoroscopic imaging system.

METHODS

Eight volunteers with stage II AAFD and seven volunteers without stage II AAFD were recruited and CT scans were performed bilateral for both groups in neutral positions. Their lateral dynamic X-ray data during the stance phase, including 14 non-flatfeet and 10 flatfeet, was collected. A computer-aided simulated light source for 3D CT model was applied to obtain the virtual images, which were matched with the dynamic X-ray images to register in the "Fluo" software, so that the spatial changes during the stance phase could be calculated.

RESULTS

During the early-stance phase, the calcaneous was more dorsiflexed, everted, and externally-rotated relative to the talus in flatfoot compared with that in non-flatfoot (p < 0.05). During the mid-stance phase, the calcaneous was more dorsiflexed and everted relative to the talus in flatfoot compared with that in non-flatfoot (p < 0.05); however, the rotation did not differ significantly between the two groups (p > 0.05). During the late-stance phase, the calcaneous was more plantarflexed, but less inverted and internally-rotated, relative to the talus in flatfoot compared with that in non-flatfoot (p < 0.05). During the early- and mid-stance phase, the navicular was more dorsiflexed, everted, and externally-rotated relative to the talus in flatfoot compared with that in non-flatfoot (p < 0.05). During the late-stance phase, the navicular was more plantarflexed, but less inverted and internally-rotated, relative to the talus in flatfoot compared with that in non-flatfoot (p < 0.05). There was no difference in the motion of cuboid between the two groups during the whole stance phase (p > 0.05).

CONCLUSIONS

During the early- and mid-stance phase, excessive motion was observed in the subtalar and talonavicular joints in stage II AAFD. During the late-stance phase, the motion of subtalar and talonavicular joints appeared to be in the dysfunction state. The current study helps better understanding the biomechanics of the hindfoot during non-flatfoot and flatfoot condition which is critical to the intervention to the AAFD using conservative treatment such as insole or surgical treatment for joint hypermotion.