Elsevier

Clinical Biomechanics

Volume 30, Issue 5, June 2015, Pages 493-499
Clinical Biomechanics

One- and multi-segment foot models lead to opposite results on ankle joint kinematics during gait: Implications for clinical assessment

https://doi.org/10.1016/j.clinbiomech.2015.03.004Get rights and content

Highlights

  • Foot model affects resultant ankle kinematics.

  • All anatomical axes are not equally affected by the foot model.

  • Flat feet children showed larger discrepancy on ankle kinematics than healthy ones.

  • Lower limb kinetics can be impacted by foot model.

Abstract

Background

Biomechanical models representing the foot as a single rigid segment are commonly used in clinical or sport evaluations. However, neglecting internal foot movements could lead to significant inaccuracies on ankle joint kinematics. The present study proposed an assessment of 3D ankle kinematic outputs using two distinct biomechanical models and their application in the clinical flat foot case.

Methods

Results of the Plug in Gait (one segment foot model) and the Oxford Foot Model (multisegment foot model) were compared for normal children (9 participants) and flat feet children (9 participants). Repeated measures of Analysis of Variance have been performed to assess the Foot model and Group effects on ankle joint kinematics.

Findings

Significant differences were observed between the two models for each group all along the gait cycle. In particular for the flat feet group, opposite results between the Oxford Foot Model and the Plug in Gait were revealed at heelstrike, with the Plug in Gait showing a 4.7° ankle dorsal flexion and 2.7° varus where the Oxford Foot Model showed a 4.8° ankle plantar flexion and 1.6° valgus.

Interpretation

Ankle joint kinematics of the flat feet group was more affected by foot modeling than normal group. Foot modeling appeared to have a strong influence on resulting ankle kinematics. Moreover, our findings showed that this influence could vary depending on the population. Studies involving ankle joint kinematic assessment should take foot modeling with caution.

Introduction

The foot is a complex anatomical structure composed of many articulated segments that allow a wide variety of movements. Modeling the foot is consequently known as a key issue in gait analysis (Deschamps et al., 2011). Classical biomechanical models, such as the Plug in Gait (PIG) (Kadaba et al., 1990), consider the foot as a mono-segmental unit linked to the tibia by the ankle joint, thus neglecting internal foot movements. Numerous multisegment foot models have been developed to overcome this limitation (Deschamps et al., 2011, Dixon et al., 2012, Baker and Robb, 2006). Among them, the Oxford Foot Model (OFM) represents the foot as three segments which are the rearfoot (calcaneum), the forefoot (metatarsal segments) and the hallux. This model is aimed at better transcribing the foot anatomy. The OFM repeatability has been validated for adults and children (Curtis et al., 2009, Stebbins et al., 2006). These multi-segment foot models undoubtedly made a consequent knowledge emerge on internal foot movements.

Even with the known limitations in mind, such as the drastic reduction of the anatomical degrees of freedom when using a mono-segment foot model, the ankle joint kinematics and kinetics computed by one-segment foot models are still used daily for clinical or sport lower limb evaluations (Moore and Dixon, 2014, Pasini Neto et al., 2012, Böhm and Döderlein, 2012, Thompson et al., 2014). As kinematics are input data for inverse dynamics computations, it is of prime interest to understand the implications of using different foot kinematic models and their influences when assessing lower limb function (Dixon et al., 2012).

Furthermore, it could be important to analyze whether the differences in ankle joint kinematics observed between two kinematic models are consistent even when the foot is highly distorted, especially in sport and clinical evaluations. Indeed in these situations, more strain can be generated within the foot and lead to a different influence of the foot model on ankle kinematics. Together with typically developing children, this study assessed idiopathic pediatric flat feet gait, a common clinical deformation (Mosca, 2010), to investigate this issue. Indeed, children displaying flexible flat feet are often a source of concern for parents and lead to a large number of orthopedic consultations (Pfeiffer et al., 2006), being conducted using clinical gait analysis techniques. This deformation is characterized by a flattening medial longitudinal arch associated with a rearfoot valgus exceeding 4° in weight bearing position. This particular situation of foot distortion can enhance the weakness of one segment foot models for gait analyses.

The aim of this study was to assess the differences in the ankle joint kinematics computed by the PIG and the OFM models, and to compare these differences between flexible flat feet children (flat group) and normal children (normal group). We hypothesized that 1) differences between the OFM and the PIG models will emerge in the ankle joint kinematics for normal children, 2) the flat feet group will show more significant differences between foot models than normal children.

Section snippets

Subjects

Nine normal children (mean 8.1 years old (SD 1.6 years old), mean 135.2 cm (SD 10 cm), mean 30.9 kg (SD 6.5 kg)) and nine flat feet children (mean 8.2 years old (SD 3.4 years old), mean 135 cm (SD 19.4 cm) and mean 34 kg (SD 13 kg) were recruited. Every participant was examined using a homogenous clinical exam, gave informed consent, while the experiment was approved by the local ethical committee. Children from the flat feet group were selected by pediatric orthopedists after a standardized clinical

Results

Repeated measure ANoVAs confirmed that, for both normal and flat feet groups, 3D ankle joint kinematics computed by the OFM and the PIG were significantly different (Fig. 2 and Table 1). These differences principally occurred about the dorsal/plantar flexion and varus/valgus axes (Fig. 2).

About the ankle flexion axis, ANoVA revealed a simple effect of foot model on ankle flexion amplitude (F(1,34) = 10.6, P < 0.001) where the PIG displayed higher amplitude compared to the OFM (PIG = mean 25.1° (SD

Discussion

The aim of this study was to propose a quantified evaluation of the differences that emerge on ankle joint kinematics while selecting different foot models. Results obtained for the ankle joint kinematics during gait using single segment model were compared to those obtained using a multisegment model in normal feet and flat feet groups.

In normal children, significant differences emerged in ankle joint kinematics in between the mono and the multisegment foot models, in accordance with our first

Conclusion

The present study brought out that ankle joint kinematics are widely dependent on foot model and groups. Considering these results, it seems natural to hypothesize that the differences would not be consistent when looking at different pathologies, which represents a major issue in clinical diagnoses and treatments. Although the importance of considering the foot as a multi-segment structure is well admitted among the biomechanical community, this study is the first one to propose a quantified

Conflict of interest

The authors declare having no conflict of interest in relation to this article.

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