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Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Walking is an important skill with positive impacts on health, function, and well-being. Many disorders impair walking and its positive impacts through a variety of complex and interrelated mechanisms. Any attempt to understand walking impairments, or the effects of interventions intended to treat these impairments, must respect this complexity. Therefore, our main objectives in conducting this study were to (1) propose a comprehensive model for quantifying the causes and consequences of walking impairments and (2) demonstrate the potential utility of the model for supporting clinical care and addressing basic scientific questions related to walking. To achieve these goals, we introduced a model, described by a directed acyclic graph, consisting of 10 nodes and 23 primary causal paths. We gave detailed descriptions of each node and path based on domain knowledge. We then demonstrated the model's utility using a large sample of gait data (N = 9504) acquired as part of routine care at a regional referral center. We analyzed five relevant examples that involved many of the model's nodes and paths. We computed causal effect magnitudes as Shapley values and displayed the overall importance of variables (mean absolute Shapley value), the variation of Shapley values with respect to underlying variables, and Shapley values for individual observations (case studies). We showed that the model was plausible, captured some well-known cause-effect relationships, provided new insights into others, and generated novel hypotheses requiring further testing through simulation or experiment. To aid in transparency, reproducibility, and future enhancements we have included an extensively commented Rmarkdown file and a deidentified data set., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2022 Schwartz 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.)

Aim: The dynamic motor control index during walking (walk-DMC) is a scaled measure of motor control derived from electromyographic analysis of the lower extremity during gait. Walk-DMC has been shown to be related to patient outcomes and there has been an increasing interest from motion analysis centers regarding using this metric in their own practice. However, the methods for computing the index reported in the literature are not consistent. Here we propose a standardized method and investigate if this leads to results that are consistent between laboratories., Method: Comparisons between three sets of typically developing controls contributed by three independent motion analysis centers are made. Comparisons are also made between the proposed and previously published methods. A program script to compute the walk-DMC was used for this study and is made freely available with this manuscript., Results: Using this script, results are highly consistent between three participating centers. The currently proposed method results in a wider distribution of walk-DMC values than those previously reported., Interpretation: Using consistent processing methods, synergy measures are equivalent between centers. The major differences between current and published data are attributed to the use of concatenation of several walking trials., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

Background: Pedobarography is a commonly used testing procedure in clinical gait analysis, yet has limited roles in quantification for treatment planning, outcome assessment, and classification. Spatial registration between plantar pressure and motion capture data allows for accurate quantitative assessment and metric development based on a typically developing cohort., Research Question: This study assesses the validity of new center of pressure based metrics of anatomically registered pedobarography data by evaluating kinematic relationships over a broad spectrum of feet and by evaluating the sensitivity of these metrics to pathologies, interventions, and outcomes in two common clinical foot pathologies., Methods: 3D trajectories from retroreflective markers were recorded to establish a single foot axis simultaneous with plantar pressure mat data spatially calibrated to a global coordinate system. Indices for clinical populations were determined as mediolateral (MLI, |MLI|, MFI) and anteroposterior (API, |API|) deviations of center of pressure excursions from typically developing feet. 198 feet were retrospectively identified to evaluate relationships between mediolateral (ML) indices and foot kinematics over a spectrum of foot pathologies. Additional feet from two broad pathologic foot types, planovalgus (PV) and cavovarus (CV), were assessed pre and post-surgery to determine sensitivity to pathology, surgical intervention, and outcomes., Results: ML indices and supination were highly correlated (r 2  > 0.5). Two mediolateral indices (MLI, MFI) and one anteroposterior index (|API|) demonstrated significant differences between typical and PV feet, with the MFI index also exhibiting significant improvement with surgery. All three mediolateral indices and |API| demonstrated differences between typical and cavovarus feet, with |API| significantly improving with surgery. Changes in API also correlated with patient goals., Significance: Spatial registration between plantar pressure center of pressure and motion capture data allows calculation of indices that reflect foot function and are sensitive to foot pathologies and treatment outcomes., Competing Interests: Declaration of Competing Interest The authors of this manuscript have no financial or personal relationships with any peoples or organizations which could inappropriately influence this work., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Introduction: Spasticity is one of the primary pathologies associated with cerebral palsy (CP), yet no definitive evidence exists to guide the appropriate level of spasticity management for an individual. Spasticity management strategies often differ by center. On one end of this strategy spectrum is a highly-interventional approach, characterized by treatments such as a selective dorsal rhizotomy (SDR), intrathecal baclofen pump (ITB), and anti-spasticity injections and medications. On the other end of the spectrum is a less interventional approach, involving minimal use of these treatments, and no SDR., Methods and Analysis: A retrospectively-matched, multi-center study protocol is described that comprehensively compares the long-term outcomes of a highly-interventional versus a minimally-interventional spasticity management strategy. We will analyze two groups of adults with spastic bilateral CP (≥21 years). In one group are individuals who underwent an SDR between the ages of 4 and 10 years, along with ongoing spasticity management during childhood and adolescence. In the other group are individuals who received minimal spasticity management and did not undergo an SDR. Individuals with prolonged use of an intrathecal baclofen (ITB) pump will be excluded. The two groups will be matched for spasticity and other important clinical characteristics at baseline. This study design improves on many of the limitations found in the existing outcome literature., Ethics and Dissemination: This study received necessary approval from the University of Minnesota and Western Institutional Review Boards. Results will be disseminated via peer-reviewed publications and conference presentations., Trial Registration Number: NCT03789786., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

A retrospective analysis of computational gait studies performed in a single lab over a 12 year period was undertaken to characterize how recommendations to perform or not to perform hamstring lengthenings were utilized by physicians and the effect on outcomes. 131 Subjects were identified as either having hamstring lengthening considered by the referring surgeon, recommended by gait analysis data, or performed. A subset of this data meeting inclusion criteria for pre- and post-surgical timeframes, and bilateral diagnosis was further analyzed to assess the efficacy of the recommendations. There was initial agreement between planned procedures and recommended procedures in just 41% of the cases. Including the cases where there was agreement, gait analysis altered the initial procedure in 54%. In the cases where the initial plan was not supported by gait data, surgeons followed gait recommendations in 77%. In subjects who underwent hamstring lengthening, when surgeons followed or agreed with gait recommendations, patients were 3.6 times more likely to experience a positive outcome., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Torsional deformities of the femur in children may occur as a result of either idiopathic or neuromuscular disorders and may be corrected with derotational osteotomies. Regardless of the underlying etiology, neither the effects of the torsional pathologies nor the alterations resulting from corrective osteotomies are well understood. A study of children with isolated femoral anteversion undergoing a single corrective procedure may assist in understanding the biomechanics of the pathology and the efficacy of surgical correction. A multicenter retrospective study included 25 subjects with idiopathic femoral anteversion who underwent femoral derotational osteotomy and had completed pre and postoperative gait analyses. Both changes with surgery and comparisons to typically developing controls were analyzed. Reduced gait pathology and expected improvements in hip rotation and foot progression were found with derotational osteotomy. Overall gait pathology and pathological differences in pelvic tilt, hip flexion moment and knee adduction moment were found comparing anteversion subjects with typically developing subjects. Following surgery, only hip rotation was significantly and clinically different from typically developing subjects, changing from relatively inward to outward. Idiopathic femoral anteversion creates multifaceted and significant alterations to normal gait and should not be considered solely a cosmetic issue. Additionally, the efficacy of derotational osteotomy is illustrated and may be more broadly applied to other conditions where pathologic femoral anteversion is present., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Gait indices are now commonly used to assess overall pathology and outcomes from studies with instrumented gait analyses. There are differences in how these indices are calculated and therefore inherent differences in their sensitivities to detect changes or differences between groups. The purpose of the current study was to examine the three most commonly used gait indices, Gillette Gait Index (GGI), Gait Deviation Index (GDI), and Gait Profile Score (GPS), comparing the statistical sensitivity and the ability to make meaningful interpretations of the clinical results. In addition, the GDI*, a log transformed and scaled version of the GPS score which closely matches the GDI was examined. For seven previous or ongoing studies representing varying gait pathologies seen in clinical laboratories, the GGI, GDI, and GPS/GDI* were calculated retrospectively. The GDI and GPS/GDI* proved to be the most sensitive measures in assessing differences pre/post-treatment or from a control population. A power analysis revealed the GDI and GDI* to be the most sensitive statistical measures (lowest sample sizes required). Subjectively, the GDI and GDI* interpretation seemed to be the most intuitive measure for assessing clinical changes. However, the gait variable sub-scores of the GPS determined several statistical differences which were not previously noted and was the only index tool for quantifying the relative contributions of specific joints or planes of motion. The GGI did not offer any advantages over the other two indices., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Planovalgus deformity is prevalent in cerebral palsy patients, but very few studies have quantitatively reported differences between planovalgus and normal foot function. Intersegmental foot kinetics have not been reported in this population. In this study, a three segment (hindfoot, forefoot, hallux) kinematic and kinetic model was applied to typically developing (n=10 subjects, 20 feet) and planovalgus (n=10 subjects, 18 feet) pediatric subjects by two clinicians for each subject. Intra-clinician and inter-clinician repeatability of kinematic variables have been previously reported. Variability of kinetic outcomes (joint moments and power) is reported and found to be equally repeatable in typically developing and planovalgus groups. Kinematic differences in the planovalgus foot including excessive ankle eversion (valgus) and plantarflexion, reduced ankle flexion range of motion, and increased midfoot joint dorsiflexion and pronation reflected the reported pathology. Contrary to clinical expectations no significant difference was observed in midfoot flexion or ankle eversion ranges of motion. Kinetic differences in planovalgus feet compared to typically developing feet included reduced ankle plantarflexion moment, ankle power and midfoot joint power., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Background: This study quantifies the three-dimensional motion of lumbar vertebrae during gait via direct in vivo measurement with the use of indwelling bone pins with retroreflective markers and motion capture. Two previous studies in which bone pins were used were limited to instrumentation of two vertebrae, and neither evaluated motions during gait. While several imaging-based studies of spinal motion have been reported, the restrictions in measurement volume that are inherent to imaging modalities are not conducive to gait applications., Methods: Eight healthy volunteers with a mean age of 25.1 years were screened to rule out pathology. Then, after local anesthesia was administered, two 1.6-mm Kirschner wires were inserted into the L1, L2, L3, L4, L5, and S1 spinous processes. The wires were clamped together, and reflective marker triads were attached to the end of each wire couple. Subjects underwent spinal computed tomography to anatomically register each vertebra to the attached triad. Subjects then walked several times in a calibrated measurement field at a self-selected speed while motion data were collected., Results: Less than 4° of lumbar intersegmental motion was found in all planes. Motions were highly consistent between subjects, resulting in small group standard deviations. The largest motions were in the coronal plane, and the middle lumbar segments exhibited greater motions than the segments cephalad and caudad to them. Intersegmental lumbar flexion and axial rotation motions were both extremely small at all levels., Conclusions: The lumbar spine chiefly acts to contribute abduction during stance and adduction during swing to balance the relative motions between the trunk and pelvis. The lumbar spine acts in concert with the thoracic spine. While the lumbar spine chiefly contributes coronal plane motion, the thoracic spine contributes the majority of the transverse plane motion. Both contribute flexion motion in an offset phase pattern., Clinical Relevance: This is a valid model for measuring the three-dimensional motion of the spine. Normative data were obtained to better understand the effects of spine disorders on vertebral motion over the gait cycle.

Several multi-segment foot models to measure the motion of intrinsic joints of the foot have been reported. Use of these models in clinical decision making is limited due to lack of rigorous validation including inter-clinician, and inter-lab variability measures. A model with thoroughly quantified variability may significantly improve the confidence in the results of such foot models. This study proposes a new clinical foot model with the underlying strategy of using separate anatomic and technical marker configurations and coordinate systems. Anatomical landmark and coordinate system identification is determined during a static subject calibration. Technical markers are located at optimal sites for dynamic motion tracking. The model is comprised of the tibia and three foot segments (hindfoot, forefoot and hallux) and inter-segmental joint angles are computed in three planes. Data collection was carried out on pediatric subjects at two sites (Site 1: n=10 subjects by two clinicians and Site 2: five subjects by one clinician). A plaster mold method was used to quantify static intra-clinician and inter-clinician marker placement variability by allowing direct comparisons of marker data between sessions for each subject. Intra-clinician and inter-clinician joint angle variability were less than 4°. For dynamic walking kinematics, intra-clinician, inter-clinician and inter-laboratory variability were less than 6° for the ankle and forefoot, but slightly higher for the hallux. Inter-trial variability accounted for 2-4° of the total dynamic variability. Results indicate the proposed foot model reduces the effects of marker placement variability on computed foot kinematics during walking compared to similar measures in previous models., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Several full body musculoskeletal models have been developed for research applications and these models may potentially be developed into useful clinical tools to assess gait pathologies. Existing full-body musculoskeletal models treat the foot as a single segment and ignore the motions of the intrinsic joints of the foot. This assumption limits the use of such models in clinical cases with significant foot deformities. Therefore, a three-segment musculoskeletal model of the foot was developed to match the segmentation of a recently developed multi-segment kinematic foot model. All the muscles and ligaments of the foot spanning the modeled joints were included. Muscle pathways were adjusted with an optimization routine to minimize the difference between the muscle flexion-extension moment arms from the model and moment arms reported in literature. The model was driven by walking data from five normal pediatric subjects (aged 10.6+/-1.57 years) and muscle forces and activation levels required to produce joint motions were calculated using an inverse dynamic analysis approach. Due to the close proximity of markers on the foot, small marker placement error during motion data collection may lead to significant differences in musculoskeletal model outcomes. Therefore, an optimization routine was developed to enforce joint constraints, optimally scale each segment length and adjust marker positions. To evaluate the model outcomes, the muscle activation patterns during walking were compared with electromyography (EMG) activation patterns reported in the literature. Model-generated muscle activation patterns were observed to be similar to the EMG activation patterns., (Published by Elsevier Ltd.)

Several functional methods to determine joint centers of rotation (CoR) and axes of rotation (AoR) have been reported in the literature. These have previously been compared using noise introduced to marker positions. The current study compares four of these methods under both rigid body and deformable body conditions using a mechanical analog of the lower extremity. In the latter condition, significant inter-marker distance changes were present in patterns directly related to the joint motion. Both hip CoR location and knee AoR location and direction are determined. Results indicate that while all methods produced accurate measures under rigid body conditions (<5mm location and <2 degrees direction), there were many differences between methods in deformable conditions. Under these conditions, the method described by Gamage and Lasenby performed better than the other methods examined. Maximum mean errors for this technique were approximately 1cm for CoR and AoR locations and 1 degrees for AoR direction.

The Gillette Gait Index (GGI) is a tool used to measure pathologic gait severity and assess outcomes. The purpose of this study is to assess the variation in calculated GGI values with different sets of control data. Five able bodied control sets from four labs were used to establish the basis of the GGI. Gait data from three pediatric patients seen pre- and post-operatively at one lab and one adult control subject that visited each lab were input to calculate GGI values. Differences in underlying control data created large differences in computed GGI values for both pathologic and able bodied subjects. Initial pre-operative GGI values calculated for the three patients with cerebral palsy using different control data sets varied widely with differences as large as 1129 and had magnitudes of improvement differing by as much as 800 (or 21%). GGI value differences greater than 250 were determined from an able bodied control subject seen at each lab, both when examining a single trial with different control sets, and when examining different trials of the same individual collected from different labs using a single control set. These results highlight the importance of the underlying control set for establishing mean values and variance in the GGI and suggest that if GGI values are compared longitudinally or between sites these comparisons should be based on a single control dataset.

Researchers have suggested that sensory cues can improve gait initiation in persons with Parkinson's disease (PD); however, there is little research that documents the effects of sensory cues on gait initiation. The purpose of this study was to examine the effects of auditory and cutaneous sensory cues on maximal speed gait initiation in person's with PD and healthy elderly. Seven persons with PD of moderate severity (mean age=69 years) and seven age, gender, and height matched healthy elders participated. Temporal, kinematic and center of pressure (COP) data were recorded as participants performed eight trials within four randomly ordered conditions (no cue (NC), a single auditory cue (SA), repetitive auditory cues (RA), and repetitive cutaneous cues (RC)). In each condition, participants were instructed to perform each gait initiation trial at their maximal speed. In all conditions, person's with PD reacted more slowly and moved less far than did the matched elders. Relative to conditions with NCs, sensory cueing resulted in decreased double limb support (DLS), and increased COP displacement and velocity in both groups. However, in both groups, displacements and velocities of the swing limb and sacrum during the sensory-cued conditions were less than those during the NC condition. These results suggest that when movement speed is a primary goal, sensory cues may interfere with swing limb and body movement outcomes during the gait initiation task in both person's with PD and healthy elders., (Copyright 2003 Elsevier B.V.)

Gait analysis models typically analyze the ankle joint complex and treat the foot as a rigid segment. Such models are inadequate for clinical decision making for patients with foot impairments. While previous multisegment foot models have been presented, no comprehensive kinematic and kinetic databases for normal gait exist. This study provides normative foot joint angles, moments and powers during adolescent gait. Eighteen subjects were evaluated using 19 retroreflective markers, six cameras, a pressure platform and a force plate. A nine-segment model determined 3D angles, 3D moments, and powers in eight joints or joint complexes. A complete sets of sagittal, coronal and frontal plane results are presented. Results indicate that single link models of the foot significantly overestimate ankle joint powers during gait. Understanding normal joint kinematics and kinetics during gait will provide a baseline for documenting impairments in patients with foot disorders.