---
title: "Proximal hip malalignment in pediatric flexible flatfoot despite preserved gait: dual-level static"
id: "plos-one-18-compensatory-proximal-malalignment-despite-preserved-macroscopic-gait-in"
canonical_url: "https://medichelpline.com/clinical-feed/plos-one-18-compensatory-proximal-malalignment-despite-preserved-macroscopic-gait-in"
content_type: "clinical_feed_article"
specialty: "Pediatrics"
source_name: "PLOS ONE (Medicine)"
source_url: "https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0358183"
published_at: "2026-09-16T14:00:00.000Z"
evidence_level: "Journal Feed"
license: "CC-BY-NC-4.0 / Informational Use"
---
# Proximal hip malalignment in pediatric flexible flatfoot despite preserved gait: dual-level static
## Provenance & Clinical Metadata
- **Canonical URL:** https://medichelpline.com/clinical-feed/plos-one-18-compensatory-proximal-malalignment-despite-preserved-macroscopic-gait-in
- **Specialty:** [Pediatrics](https://medichelpline.com/clinical-feed/pediatrics.md)
- **Primary Source:** PLOS ONE (Medicine)
- **Source URL:** [Original Journal Publication](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0358183)
- **Published At:** 2026-09-16T14:00:00.000Z
- **Evidence Rating:** Journal Feed
## Executive GIST (TL;DR)
- This study analyzed 153 children (306 lower extremities; 25 unilateral, 128 bilateral) with **pediatric flexible flatfoot** using a high-precision motion capture system to examine both static 3D alignment and dynamic gait kinematics. - A dual-level analytical strategy was applied: subject-level comparisons of macroscopic spatiotemporal parameters (Mann–Whitney U test) and limb-level analyses using linear mixed-effects models (LMMs) that treated subject as a random effect and adjusted for age, BMI, and unilateral leg length. - At the subject and limb levels, no significant differences were found in core spatiotemporal parameters such as mean velocity, cadence/frequency, and step width (P > 0.05), indicating preserved macroscopic gait. - Limb-level static 3D alignment showed a statistically significant reduction in external static **Hip Rotation** on the flatfoot side versus the normal side (−2.11° ± 0.67° vs. −5.79° ± 1.79°, P = 0.043), representing relative internal rotation. - During dynamic walking, the Hip Abduction/Adduction **Gait Variable Score (GVS)** was significantly increased on the flatfoot side (P = 0.032), indicating frontal-plane hip kinematic deviation. - Global gait indices including the **Gait Profile Score (GPS)** and Gait Deviation Index (GDI) did not show significant overall between-group differences. - The findings indicate subtle proximal compensations in hip alignment and frontal-plane hip dynamics occurring despite largely normal macroscopic gait measures, supporting the need for broader kinetic-chain assessment in clinical evaluation and follow-up. - Raw data are stored offline at the authors’ institution and are not publicly available; access requests must follow the institutional process. Funding was provided by Beijing Traditional Chinese Medicine Science and Technology Development Fund; authors declared no competing interests.
## Clinical Analysis & Structured Key Points
Compensatory proximal malalignment despite preserved macroscopic gait in pediatric flexible flatfoot: A dual-level analysis of static alignment and dynamic kinematics | PLOS One Browse Subject Areas ? Click through the PLOS taxonomy to find articles in your field. For more information about PLOS Subject Areas, click here . Article Authors Metrics Comments Media Coverage Reader Comments Figures Figures Abstract Background & objective Previous biomechanical studies on pediatric flexible flatfoot have treated the subject as a single analytical unit, thus failing to elucidate mechanical transmission within the lower extremity closed kinetic chain. This study investigates the impact of distal arch collapse on macroscopic gait parameters, static joint alignment, and dynamic kinematic deviation by integrating a dual-level analytical strategy at both the subject and individual limb levels. Methods 153 children with pediatric flexible flatfoot (25 unilateral, 128 bilateral) were included, and 3D gait data from 306 lower extremities were analyzed. At the subject level, macroscopic spatiotemporal parameters were compared using the Mann-Whitney U test. At the limb level, linear mixed-effects models (LMMs) compared static 3D joint angles and Gait Variable Scores (GVS) between normal feet and flatfeet, treating subject as a random effect and adjusting for age, body mass index (BMI), and unilateral leg length. Results At both the subject and limb levels, no significant between-group differences were observed in any core spatiotemporal parameters (e.g., Mean Velocity, Frequency, and Step Width) (P > 0.05). Regarding static joint alignment at the limb level, the static Hip Rotation angle on the flatfoot side exhibited significantly less external rotation (i.e., relative internal rotation) compared to the normal side (−2.11° ± 0.67° vs. −5.79° ± 1.79°, P = 0.043). During dynamic walking, the Hip Abduction/Adduction GVS on the flatfoot side was significantly elevated ( P = 0.032). However, comprehensive gait indices, including the GDI and GPS, showed no significant overall between-group differences. Conclusion Pediatric flexible flatfoot was associated with subtle proximal biomechanical alterations despite preserved macroscopic gait characteristics. Changes in static hip alignment and dynamic frontal-plane hip kinematics may therefore provide complementary information beyond conventional gait measures, supporting a broader kinetic-chain assessment in clinical evaluation and follow-up. Citation: Wang H, Li M, Liang X, Wang W, Luo P, Zhang J, et al. (2026) Compensatory proximal malalignment despite preserved macroscopic gait in pediatric flexible flatfoot: A dual-level analysis of static alignment and dynamic kinematics. PLoS One 21(9): e0358183. https://doi.org/10.1371/journal.pone.0358183 Editor: Rohan Kothurkar, Somaiya Vidyavihar University K J Somaiya College of Engineering, INDIA Received: June 20, 2026; Accepted: August 27, 2026; Published: September 16, 2026 Copyright: © 2026 Wang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: The raw experimental data are stored on an offline computer in the Third Department of Sports Medicine, Wangjing Hospital, China Academy of Chinese Medical Sciences, and managed by a designated full-time staff member. The data cannot be publicly released due to institutional internal data management regulations. Researchers who meet relevant access requirements may submit formal data access applications to the institutional research office. Institutional contact for data access: Research Management Office, Wangjing Hospital, China Academy of Chinese Medical Sciences Email: wjyyyjkt@163.com . Funding: This study was supported by the Beijing Traditional Chinese Medicine Science and Technology Development Fund (Project Nos. BJZYZD-2025-06 and BJZYQN-2025-38). The funders participated in study design and the decision to publish, but had no role in data collection and analysis or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist. Introduction Pediatric flexible flatfoot (FFT) is a common musculoskeletal disorder of the lower extremities. It is primarily characterized by the collapse of the medial longitudinal arch and excessive subtalar joint eversion [ 1 , 2 ]. These structural abnormalities significantly alter the mechanical characteristics of the lower extremities. Although many children remain asymptomatic in the short term, clinical observations indicate that persistent structural deformities can lead to altered stress distribution, lower extremity fatigue, and an elevated risk of injury [ 3 – 5 ] Current evidence suggests that the biomechanical consequences of FFT involve complex structural and sensorimotor adaptations that extend well beyond local foot and ankle complex mechanics [ 6 ]. Specifically, within the closed kinetic chain of the lower extremities, distal instability is transmitted proximally, thereby altering the kinematics and dynamic motor control of proximal joints [ 7 – 9 ]. According to biomechanical principles, static alignment significantly influences dynamic function [ 10 ] Clinically, adaptive changes within the closed kinetic chain of the lower extremities often manifest as altered neuromuscular recruitment patterns [ 11 ]and an increased demand on proximal stabilizing muscle groups to maintain posture and distal control [ 12 ]. These muscle groups must counteract the abnormal joint moments (e.g., excessive or misdirected inversion/eversion and rotational moments) generated by the flatfoot deformity to prevent further biomechanical dysfunction.Although these functional compensations persist to maintain overall walking efficiency, this motor strategy—rooted in an initial structural malalignment—may induce an occult loss of postural stability. Furthermore, prolonged and unmanaged proximal compensation can lead to adverse consequences, including accelerated joint wear [ 13 ], patellofemoral pain syndrome [ 14 ], and altered force transmission across the articular surfaces of the hip and knee [ 15 ]. However, research concerning the biomechanical consequences of FFT—particularly regarding its systematic impact on overall postural control and proximal joints of the lower extremities—remains relatively limited. First, previous studies have predominantly focused on joint angle alterations during dynamic gait cycles, frequently overlooking potential three-dimensional (3D) kinematic abnormalities during static stance. Consequently, few studies have systematically explored how static 3D joint malalignments translate into dynamic gait deviations. Second, when evaluating dynamic gait quality, isolated spatiotemporal parameters often mask multi-planar kinematic deficits [ 16 ]. The incorporation of objective, comprehensive gait indices—such as the Gait Profile Score (GPS) and Gait Variable Scores (GVS)—can more sensitively quantify neuromuscular adaptability to distal deformities [ 17 ]. More importantly, regarding research design and statistical methodology, prior studies have largely utilized the subject as a single analytical unit. This approach overlooks the fact that the closed kinetic chain of the lower extremities is fundamentally a limb-specific mechanical transmission process. Clinically, FFT presents with either unilateral or bilateral involvement; grouping solely by subject may obscure critical biomechanical differences between an unaffected limb and a collapsed arch within the same patient. Furthermore, the uncontrolled pooling of bilateral limb data violates the assumption of statistical independence. Finally, because pediatric gait is significantly influenced by growth and development, studies failing to strictly control for confounding factors, such as age and body mass index (BMI), often yield inconsistent and less robust conclusions [ 18 ]. To address these limitations, this study employed a high-precision infrared optoelectronic motion capture system and a dual-level analytical strategy integrating both the limb and subject levels. By utilizing linear mixed-effects models (LMMs) to rigorously control for within-subject correlations and developmental covariates, we compared the biomechanical characteristics of normal feet and flatfeet, treating the individual lower extremity as the primary unit of analysis. Specifically, this study aims to investigate the following two primary objectives: (1) Assessing static differences: To quantitatively compare the 3D spatial alignment of the lower extremity joints between the two groups during static stance; (2) Quantifying dynamic function and gait deviations: To determine whether static structural alterations influence the spatiotemporal parameters of dynamic walking, and to reveal underlying multi-planar kinematic deviations using comprehensive gait indices (i.e., GDI, GPS, and GVS). Materials and methods Research design This single-center, retrospective observational study was conducted using data from the clinical gait database of the Third Department of Sports Medicine, Wangjing Hospital, China Academy of Chinese Medical Sciences, spanning the period from 2025 to 2026.All research data included in this study were accessed on 01/02/2026 from the clinical gait database. Ethical approval and informed consent This study protocol was approved by the Ethics Committee of Wangjing Hospital, China Academy of Chinese Medical Sciences (Approval No.: WJEC-KT-2025–064-P001). Given the retrospective nature of this study, which involved no additional interventions or risks to the subjects, the requirement for informed consent was waived by the Ethics Committee. All data were strictly anonymized prior to analysis; personal identifying information (e.g., names and medical record numbers) was removed and replaced with unique identification codes. The collection, storage, and analysis of all data were conducted in strict accordance with the ethical principles outlined in the Declaration of Helsinki. Participants Inclusion criteria. (1) Patients who underwent 3D gait analysis and arch index measurement at our institution between January and December 2025;(2) A confirmed clinical diagnosis of FFT, established via physical examination and plantar pressure analysis (diagnostic reference standard: arch index > 0.28) [ 19 ];(3) Aged between 6 and 18 years;(4) Availability of complete arch index and 3D gait analysis data, without missing key parameters. Exclusion criteria. (1) Presence of concomitant neurological or neuromuscular disorders (e.g., cerebral palsy, poliomyelitis, peripheral neuropathy, or muscular diseases);(2) A history of lower extremity fracture, dislocation, joint replacement, or severe musculoskeletal deformity;(3) Diagnosis of inflammatory or degenerative joint diseases (e.g., rheumatoid arthritis, ankylosing spondylitis, or osteoarthritis);(4) Receipt of lower extremity surgery, orthotic interventions (bracing), or standardized rehabilitation within the 6 months prior to assessment;(5) Presence of lower extremity pain, limited mobility, or any other condition affecting natural gait during the assessment. Grouping and sample size. Based on the arch index and the laterality of the deformity, patients were categorized into a unilateral flatfoot group (n = 25) and a bilateral flatfoot group (n = 128). This yielded a total of 281 flatfeet and 25 normal feet for limb-level analysis. The sample size was determined by the number of eligible cases available during the study period; no a priori power analysis was conducted. Data collection Arch Index Measurement: The BENECOR plantar pressure assessment system (Beijing Zhengxing Medical Technology Co., Ltd., Beijing, China) was utilized to simultaneously collect plantar pressure and morphological data. The arch index was calculated automatically, with a value > 0.28 serving as the diagnostic threshold for FFT. Gait Parameter Acquisition: Three-dimensional gait data were acquired using an 8-camera infrared motion capture system (SMART-D 400, BTS Bioengineering, Milan, Italy) at a sampling rate of 100 Hz, integrated with synchronized force platforms sampling at 1000 Hz. Testing protocol All assessments were administered by two uniformly trained clinicians. Testing was conducted in a standardized gait laboratory equipped with an 8-meter walkway, under controlled environmental conditions (i.e., level surface, ambient temperature, and absence of intense light interference). Initially, basic anthropometric indices (height, weight, and BMI) and specific lower extremity parameters (including bilateral leg length, pelvic width, and pelvic depth) were recorded. All measurements were performed in duplicate, and the mean values were utilized for anthropometric scaling in the subsequent biomechanical model to normalize individual differences. Subsequently, plantar pressure distribution was recorded to calculate the bilateral arch index. Subjects stood barefoot in the center of the force platform with their arms resting naturally at their sides. The system synchronously acquired the plantar pressure data; this procedure was repeated twice to obtain an average value. Following arch assessment, 22 retroreflective markers were attached to specific anatomical landmarks using hypoallergenic double-sided tape, in accordance with the Helen Hayes marker set [ 20 , 21 ]. These landmarks included the vertebra prominens (C7), bilateral acromion processes, bilateral anterior superior iliac spines (ASIS), midpoint of the posterior superior iliac spines (PSIS), and bilaterally on the greater trochanters, lateral and medial femoral condyles, fibular heads, lateral and medial malleoli, between the first and second metatarsal heads, and the calcaneus. For static calibration, subjects stood barefoot in the center of the capture volume in a neutral stance with their arms abducted horizontally for 5 seconds. This allowed for the spatial calibration of both the 3D infrared motion capture system and the force platforms. Post-calibration, the medial malleolus and medial femoral condyle markers were removed bilaterally to prevent marker collision and interference during dynamic walking trials. Subjects were then instructed to walk barefoot along the 8-meter walkway at a self-selected, comfortable pace. Following a period of acclimatization to the testing environment, each subject performed three walking trials, and for each trial a minimum of two valid, complete gait cycles were acquired. The data were then averaged across the three trials for statistical analysis to minimize intra-individual variability and ensure data reliability. The following specific biomechanical indices were extracted for analysis: (1) Spatiotemporal parameters: Stride Time, Stance Time, Swing Time, Stance Phase, Swing Phase, Single Support Phase, Double Support Phase, Mean Velocity, Frequency, Stride Length, Step Length, and Step Width; (2) Static joint angle parameters: Pelvis Tilt, Pelvis Obliquity, Pelvis Rotation, Hip Flexion/Extension, Hip Abduction/Adduction, Hip Rotation, Knee Flexion/Extension, Ankle Dorsi/Plantarflexion, and Foot Progression Angle; (3) Comprehensive gait indices: The Gait Deviation Index (GDI) was utilized to assess overall gait pathology; the Gait Profile Score (GPS) was employed to evaluate gait asymmetry and quantify the overall deviation of kinematic variables. Furthermore, the Gait Variable Score (GVS), which decomposes the GPS across nine specific kinematic variables, was used to evaluate the deviation of individual joint kinematics. Statistical analysis All statistical analyses were performed using SPSS software (version 26.0; IBM Corp., Armonk, NY, USA). The Shapiro-Wilk test was utilized to assess the normality of continuous variables. Normally distributed continuous variables are presented as mean ± standard deviation (SD), whereas non-normally distributed data are expressed as median (interquartile range, IQR). To evaluate local mechanical transmission within the closed kinetic chain of the lower extremities, the individual limb was selected as the unit of analysis for static 3D joint angles, spatiotemporal parameters, and comprehensive gait indices (GDI, GPS, and GVS). Given the nested structure of the data (i.e., the inherent correlation between bilateral limbs within the same subject), linear mixed-effects models (LMMs) were employed to compare parameter differences between normal feet and flatfeet with medial longitudinal arch collapse. In these models, the diagnosis of FFT (arch index > 0.28) was designated as a fixed effect, while subject ID was included as a random intercept to account for within-subject bilateral non-independence. To rigorously control for the confounding effects of pediatric growth and development on joint kinematics and gait, age, body mass index (BMI), and unilateral leg length were included as covariates. A compound symmetry covariance structure was specified for the models. The LMM results are reported as estimated marginal means (EMMs) with standard errors (SEs). A P-value 0.05). This indicates that during level walking, the flatfoot deformity does not d
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