Elsevier

Clinical Biomechanics

Volume 71, January 2020, Pages 208-213
Clinical Biomechanics

Can pedobarography predict the occurrence of heel rocker in children with lower limb spasticity?

https://doi.org/10.1016/j.clinbiomech.2019.10.022Get rights and content

Highlights

  • We present new pedobarography measures to quantify the centre-of-pressure trajectory.

  • Point of initial contact and rollback were validated against three-dimensional gait analysis.

  • Point of initial contact and rollback predict heel rocker with high accuracy.

  • Point of initial contact and rollback provide a sensitive measure of foot contact pattern.

Abstract

Background

Pedobarography software calculates the centre-of-pressure trajectory in relation to the foot to quantify foot contact patterns. This study presents two new pedobarography measures using the centre-of-pressure trajectory to assess heel rocker.

Methods

To validate these pedobarography measures against 3D gait analysis, emed®-x and Vicon Nexus gait analysis data were captured from 25 children aged 8–16 years (11 male) with unilateral (n = 18) and bilateral (n = 7) cerebral palsy or acquired brain injury. 3D gait analysis identified whether heel rocker was intact (n = 22 feet) or absent (n = 28 feet) based on centre-of-pressure at initial contact and the ankle kinematic curve between 0 and 2% of the gait cycle. Pedobarography measures calculated from the initial centre-of-pressure point were the distance to the heel (point of initial contact) and to the most posterior point of the trajectory (rollback), reported as a percentage of foot length.

Findings

The median point of initial contact in limbs with an intact heel rocker was 9% (range 7–12%) and median rollback was 0% (range 0–0.2%), whereas the median point of initial contact in limbs with an absent heel rocker was 58% (range 8–78%) and rollback was 18% (range 0–40%). Point of initial contact is the more accurate method for predicting heel rocker, with a threshold of 14% of foot length identifying the correct heel rocker status in 94% of cases.

Interpretation

Point of initial contact can assess heel rocker with high accuracy. Both point of initial contact and rollback provide sensitive information on foot strike pattern, enhancing the utility of pedobarography.

Introduction

Spasticity, muscle weakness and compromised selective motor control are common features in children with neuromuscular disorders. The severity of these features tends to be more problematic in the shank and foot muscles (Fowler et al., 2010; Wiley and Damiano, 1998). As a result, many children with disorders of the neuromuscular system, including children with spastic cerebral palsy, are unable to position the foot effectively at initial contact. Overactivity of the ankle plantarflexor muscles or weak ankle dorsiflexor muscles result in forefoot or midfoot contact with the floor, which disrupts the normal heel-to-toe foot contact pattern and the function of the heel rocker (Davids, 2009; Perry and Burnfield, 2010).

The heel rocker, also known as the first rocker, is one of the three rockers proposed by Perry to describe the action of the ankle and foot as the body progresses forward over the stance limb (Perry, 1992). The heel rocker occurs during loading response and results from the ground reaction force acting on the tuberosity of the calcaneus as it contacts the ground, causing the foot to roll into plantarflexion. An intact heel rocker is dependent on appropriate pre-positioning of the foot in terminal swing, one of the prerequisites of normal gait (Gage and Schwartz, 2009). Disruption of this mechanism affects stability in stance, forward progression, step length and efficiency of gait (Perry et al., 2003). Although gait problems in children with cerebral palsy are frequently complex, inadequate positioning of the foot may be the primary gait impairment for some children with mild cerebral palsy. In these children, improving foot position at initial contact is often an aim of interventions such as botulinum toxin injections, serial casting and functional electrical stimulation.

Three-dimensional gait analysis (3DGA) is considered best practice in the assessment of gait problems in children with cerebral palsy. While observational gait analysis is convenient and quick, it is known to have low accuracy and 3DGA is accepted as the superior method for quantifying lower limb joint motion during walking (Williams et al., 2009). Specialised foot models can be used with 3DGA to obtain the most detailed information on foot and ankle kinematics but these are not routinely used in clinical gait analysis. Most centres therefore assess ankle motion and heel rocker using conventional 3DGA. However, the cost, time and expertise associated with 3DGA often excludes it from use as a routine outcome measure, and its availability is generally limited to specialist centres.

Pedobarography platform systems measure plantar pressure distributions beneath the foot to quantify pressure distribution, pressure magnitude and progression of the centre-of-pressure (CoP) as the participant walks barefoot over a force plate embedded in a dense rubber walkway (Jameson et al., 2008). In contrast to 3DGA, pedobarography can usually be completed in <20 min and requires less specialised expertise to perform. Due to the complex nature of gait in cerebral palsy, pedobarography is ideally used with 3DGA to provide complimentary information on foot dynamics. When foot posture is the primary area of interest however, pedobarography may provide sufficient information to answer clinical questions without the need for concurrent 3DGA. To optimise the information gained when using pedobarography as a primary assessment tool, methods to quantify heel-to-toe loading of the foot are required.

The CoP trajectory can be plotted from pedobarography data in relation to the plantar surface of the foot to produce 2D coordinates. This provides a visual representation of the CoP trajectory in the antero-posterior and medio-lateral planes. Pedobarography data has been used to document and classify position and progression of the COP through stance phase in typically developing and pathological populations (Bowen et al., 1998; Jameson et al., 2008). To our knowledge however, there is currently no published method to quantify progression of the CoP in the antero-posterior plane and compare to a non-pathological foot contact pattern. Abnormal pressure distribution under the foot during gait in children with footdrop or flexible equinus deformity is reflected by altered movement of the CoP trajectory. Instead of moving from heel to toe, the CoP trajectory begins with initial contact at the forefoot or midfoot and moves posteriorly toward the heel (“rollback”), before moving anteriorly (Fig. 1). An altered point of initial contact and the presence of rollback both imply an absent heel rocker. While a CoP trajectory starting at the forefoot can always be associated with an absent heel rocker, there is currently no method of predicting heel rocker status in trajectories that begin in the posterior third of the foot. A measurement that quantifies progression of the CoP with reference to a normal trajectory would provide additional information to increase the utility of pedobarography in the assessment of children with disorders such as cerebral palsy.

The aim of this study was to validate the use of two new pedobarography measures, the point of initial contact (PIC) and the magnitude of rollback, to detect the status of the heel rocker compared to 3DGA in children with lower limb spasticity. We also present reference values for PIC and rollback, collected from 120 typically developing children.

Section snippets

Children with lower limb spasticity

Twenty-five independently ambulant children with lower limb spasticity were selected from the database of the Paediatric Gait Analysis Service of New South Wales. Children were included if they had undergone 3DGA and pedobarography as part of their clinical care and if they demonstrated sufficient foot contact to calculate foot length from the pedobarography software. Ethics approval for use of clinical data in research was obtained from the Sydney Children's Hospitals Network Human Research

Results

Fifty limbs from 25 children with lower limb spasticity (11 males, 14 females) were analysed. Twenty-two children had a diagnosis of cerebral palsy, two had a brain injury sustained after the age of two years, and one had a diagnosis of incontinentia pigmenti. Five children were classified as having a unilateral distribution affecting the left side, 13 children had a unilateral distribution affecting the right side and seven children were bilaterally affected. Descriptive characteristics for

Discussion

Data from both limbs of each participant were analysed. There are well-documented conceptual and statistical problems that can arise from the inclusion of data from two feet from a single participant, as feet are unlikely to respond independently (Menz, 2004; Sutton et al., 1997). This can result in falsely narrow confidence intervals and invalid results. However, there are statistical methods that can overcome this problem by taking the correlation between feet into account. One method is the

Conclusions

PIC and rollback measured by pedobarography can generally distinguish an intact from an absent heel rocker, as measured by 3DGA. Although our results show little difference between the two measures, we have noted that a foot-flat position at initial contact can be associated with little or no rollback. It is therefore likely that PIC is the more accurate of the two measures for predicting heel rocker, with a threshold of 14% of foot length identifying the correct heel rocker status in 94% of

Acknowledgments

We are grateful to Elizabeth Barnes for her assistance with statistical analysis.

This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors. The 1000 Norms Project was supported by grants from the National Health and Medical Research Council of Australia Centre for Research Excellence in Neuromuscular Disorders (NHMRC #1031893) and Australian Podiatry Education and Research Foundation, as well as scholarship funding from the

Declaration of competing interest

No conflicts of interest are declared.

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