Pediatric flexible flatfoot (FFT) is characterized by collapse of the medial longitudinal arch and excessive subtalar eversion. Although many affected children are asymptomatic in the short term, persistent structural deformity can alter lower extremity mechanics and transmit distal instability proximally through the closed kinetic chain. Prior research has often analyzed patients as a single unit or focused only on dynamic gait angles, limiting insight into how static three-dimensional (3D) joint alignment relates to dynamic kinematic deviations. This study used a dual-level approach to examine whether distal arch collapse in FFT influences macroscopic gait parameters, static 3D joint alignment, and dynamic kinematics.
The primary aims were: (1) to compare static 3D alignment of lower-extremity joints between normal feet and flatfeet during static stance, and (2) to determine whether static structural alterations are reflected in spatiotemporal gait measures or in multi-planar kinematic indices, including the Gait Profile Score (GPS), Gait Variable Scores (GVS), and Gait Deviation Index (GDI).
This single-center, retrospective observational study used clinical gait data from the Third Department of Sports Medicine, Wangjing Hospital (data accessed 01/02/2026). The cohort comprised 153 children with clinically diagnosed pediatric flexible flatfoot, including 25 with unilateral involvement and 128 with bilateral involvement, resulting in 306 lower extremities analyzed.
A high-precision infrared optoelectronic motion capture system collected 3D gait and static alignment data. Analyses were performed at two levels: at the subject level, macroscopic spatiotemporal variables (for example, mean velocity, cadence/frequency, and step width) were compared using the Mann–Whitney U test; at the limb level, linear mixed-effects models (LMMs) were applied to compare static 3D joint angles and Gait Variable Scores between normal feet and flatfeet. LMMs treated subject as a random effect and adjusted for age, body mass index (BMI), and unilateral leg length to account for within-subject correlations and developmental covariates.
Key outcome measures included static 3D joint angles at the hip, knee, and ankle; dynamic GVS for selected joint motions; and global indices (GPS and GDI) to quantify overall gait deviation.
The sample included 153 children and 306 lower extremities. At both the subject and limb levels, no significant between-group differences were observed in core spatiotemporal parameters (mean velocity, frequency/cadence, step width) (P > 0.05), indicating preserved macroscopic gait characteristics in this cohort.
At the limb level, static 3D alignment analysis identified a statistically significant change in hip rotation: the static Hip Rotation angle on the flatfoot side exhibited less external rotation (i.e., relative internal rotation) compared with the normal side (−2.11° ± 0.67° vs. −5.79° ± 1.79°, P = 0.043).
Dynamic gait analysis demonstrated a significant increase in Hip Abduction/Adduction GVS on the flatfoot side (P = 0.032), indicating greater frontal-plane hip kinematic deviation during walking. Despite this localized kinematic difference, comprehensive gait indices—GPS and GDI—did not differ significantly between groups, suggesting that global gait quality remained comparable.
Using a dual-level design and mixed-effects modeling, this study found that pediatric FFT can be associated with subtle proximal biomechanical changes despite otherwise preserved macroscopic gait parameters. Specifically, the combination of reduced static hip external rotation and increased frontal-plane hip GVS on the flatfoot side suggests compensatory proximal malalignment and altered hip dynamics within the closed kinetic chain.
These results support the conceptual model in which distal structural instability (arch collapse) can transmit mechanical consequences proximally, eliciting static alignment changes and task-specific kinematic adaptations. The absence of significant differences in gross spatiotemporal measures and in global gait indices (GPS, GDI) suggests that common clinical gait metrics may not detect these more subtle, limb-specific adaptations.
Clinically, the findings imply that assessment of children with FFT may benefit from a broader kinetic-chain approach that includes static 3D alignment measures and targeted multi-planar kinematic indices, rather than relying solely on macroscopic spatiotemporal variables or overall gait scores.
In this cohort of children with pediatric flexible flatfoot, macroscopic gait measures were largely preserved, but limb-level analyses revealed compensatory proximal malalignment manifested as reduced static hip external rotation and increased frontal-plane hip GVS. These subtle proximal changes indicate that static and task-specific dynamic assessments may provide complementary information beyond conventional gait measures and support incorporating kinetic-chain evaluation into clinical assessment and follow-up.
The raw experimental data are stored offline at the Third Department of Sports Medicine, Wangjing Hospital, China Academy of Chinese Medical Sciences, and are managed under institutional data management regulations; they are not publicly released. Researchers meeting institutional access requirements may apply to the Research Management Office at Wangjing Hospital (wjyyyjkt@163.com) for data access.
This study was supported by the Beijing Traditional Chinese Medicine Science and Technology Development Fund (project numbers reported in the source). The authors declared no competing interests.