Elsevier

Gait & Posture

Volume 36, Issue 3, July 2012, Pages 600-604
Gait & Posture

Differences in the dynamic gait stability of children with cerebral palsy and typically developing children

https://doi.org/10.1016/j.gaitpost.2012.05.029Get rights and content

Abstract

The aim of this investigation was to evaluate the differences in the dynamic gait stability of children with cerebral palsy (CP) and typically developing (TD) children. The participants walked on a treadmill for 2 min as a motion capture system assessed the walking kinematics. Floquet analysis was used to quantify the rate of dissipation of disturbances that were present in the walking kinematics, and the variability measures were used to assess the magnitude of the disturbances present in the step length and width. The Floquet multipliers, step width and length values were correlated with Sections D and E of the Gross Motor Function Measure (GMFM). The children with CP had a larger Floquet multiplier and used a wider step width than the TD children. The magnitude of the maximum Floquet multiplier was positively correlated with the step width. Furthermore, the magnitude of the maximum Floquet multiplier and the step width were negatively correlated with the score on Section E of the GMFM. Lastly, the children with CP used a more variable step length than the TD children. These results suggest that children with CP have poor dynamic gait stability because they require more strides to dissipate the disturbances that are present in their walking pattern. In effort to stabilize these disturbances, the children with CP appear to utilize a wider step width and modulate their step length. Overall the inability to effectively dissipate the gait disturbances may be correlated with the child's ability to perform a wide range of gross motor skills (e.g., step over obstacles, jump, walk up stairs).

Highlights

► Floquet analysis and variability measures were used to assess gait stability. ► Sections E and D of the GMFM were used to assess the gross motor abilities. ► The largest Floquet multiplier (FM) was greater for the children with CP. ► Children with CP had a wider step width and a more variable step length. ► Step width and FM were negatively correlated with section D of the GMFM.

Introduction

Cerebral palsy (CP) is a neurologic disorder that results from a defect or insult to the immature brain. Although the brain insult does not progressively worsen, there is often an accumulation of musculoskeletal impairments that result in slower walking speed, a shorter-stride length, and more time spent in double support [1], [2]. It has been speculated that these gait changes reflect the unstable walking pattern seen in these children. Although it is well recognized that children with CP have poor balance and a higher incidence of falls [3], few efforts have been made to quantify the dynamic walking stability of these children. Rather, the majority of the scientific literature in this area has focused on using standing posture measurements to assess the balance instabilities seen in these children [4], [5]. The problem with this approach is that static balance tests do not correlate well with measures of dynamic gait stability or the prediction of falls [6], [7]. Hence, standing balance measures may not be the best metric for assessing the dynamic gait stability of children with CP.

In general, bipedal walking is inherently unstable because the center of mass (COM) is in a constant state of fluctuation, and may exceed the base of support during single support [8], [9]. In spite of this, the walking pattern remains dynamically stable because the COM is decelerated and redirected to remain within the base of support during the double support period [8], [9]. In typically developing children, the COM has the largest amount of displacement and acceleration in the forward direction [8], [10], and is stabilized by adjusting the step length [11]. In a similar fashion, the step width is also actively modulated to redirect the COM in the frontal plane to remain within the base of support [11], [12].

A considerable amount of experimental evidence has shown that the variability present in the step length and width is related to the balance impairments seen in adults with neurological impairments [13], [14], [15], [16]. In these studies, a greater amount of variability is thought to reflect larger foot placement errors that may result in the loss of balance. Only recently have the variability concepts begun to infiltrate the current CP literature where it has been shown that children with CP have a more variable step length [17]. However, these initial results should be interpreted with caution because variability metrics do not provide direct information on how the neuromuscular system recovers from disturbances that are present in the walking pattern [18]. Rather variability measures only provide an indication of the overall magnitude of the disturbances present in the walking pattern. Furthermore, variations in the walking pattern may not always be related to poor gait stability. It is alternatively possible that an increased amount of variation in the step length and width may also indicate that the child has greater adaptability for overcoming disturbances in the gait pattern [11], [12]. This paradox remains as a limitation for the application of variability measures, such as standard deviation and coefficient of variation, for effectively quantifying the dynamic walking gait stability of children with CP.

Floquet analysis is a well-established technique that has been successfully used to quantify the dynamic stability of the unperturbed walking patterns of humans [19], [20], [21], [22], [23]. The stability of the movement pattern can be assessed based on the rate of change of a set of state variables that quantify the behavior of the joint kinematics. Experimental data has shown that the state variables that define the walking kinematics oscillate in a rhythmic pattern and form a closed loop trajectory or limit cycle (Fig. 1) [19], [20]. Floquet analysis quantifies the rate that the walking pattern returns back to the limit cycle trajectory after experiencing a disturbance. A walking pattern is less stable if it takes more strides to return back to the limit cycle trajectory [19], [20], [21], [22], [23]. The Floquet multipliers are used to quantify the rate that the gait pattern returns back to the limit cycle trajectory. The maximum Floquet multiplier dominates the behavioral change in the gait pattern and is used to define the rate of change in the gait pattern. A maximum Floquet multiplier that is closer to one indicates that it takes more strides to dissipate the disturbances [19], [20], [21], [22], [23].

The purpose of this investigation was (1) to determine if there are differences in the maximum Floquet multipliers calculated from the walking patterns of children with CP and typically developing (TD) children, (2) to determine if the largest Floquet multiplier is related to the standing and walking clinical Gross Motor Function Measure (GMFM) scores for children with CP, (3) to determine if children with CP have greater variations in their step width and length than TD children, (4) to determine if the amount of variability in the step width and length is related to the clinical GMFM scores for children with CP.

Section snippets

Methods

The University Institutional Review Board approved all experimental procedures, and the parents consented and the children assented to participating in the experiment. Nine children with spastic diplegic CP (age = 7.8 ± 2.8 yrs), and six typically developing (TD) children (age = 8.0 ± 2.4 yrs) participated in this investigation. The children with CP had a Gross Motor Function Classification System level between I and II, and wore their prescribed ankle-foot orthosis during the experiment. Sections D

Results

There was no difference in the walking speeds used by the children with CP and the TD children during the experiment (CP = 0.79 ± 0.05 m/s; TD = 0.81 ± 0.03 m/s; p = 0.28). The children with CP had a significantly (p = 0.03) larger maximum Floquet multiplier than the TD children, which indicated that the CP children required more strides to dissipate disturbances that were encountered during walking (Fig. 2). There was a negative correlation between GMFM Section E scores and the magnitude of the maximum

Discussion

The gait patterns of the children with CP had a larger maximum Floquet multiplier than the TD children, which indicated that children with CP required more strides to dissipate the disturbances that were present in their walking pattern. The experimental work of Granata and colleagues [26] implied that there might be link between the magnitude of the maximum Floquet multiplier and the probability of a future fall occurring. Hence, it is possible that the inability to quickly dissipate the

Conflict of interest statement

The authors have no conflicts of interest for the present work.

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