Quantitative Study of Walker-Assisted Gait in Children With Celebral Palsy

8/12/2019 Quantitative Study of Walker-Assisted Gait in Children With Celebral Palsy

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Quantitative Study of Walker Assisted Gait

in Children With Cerebral Palsy:

Anterior Versus Posterior Walkers

R. Bachschmidt G . F. Harr is J Ackman

S

Hassani M. Carter A. Caudill

K. Reiners W.

Olson P .

Smith

Shriners Hosp ital fo r C hildren

Chicago IL 6 7 7

J . Klein

Department of

Biostatistics

Medical College

of

Wisconsin

Milwaukee WI 53226

Abstract

Many children with cerebral palsy require walkers to achieve functional ambulation, yet

little scientific study has been done to understand the mechanics of usage. Th e objective

of this work was to provide a quantitative pilot comparison of ambulation with anterior

and posterio r walkers in children with cereb ral palsy using temporal-spatial gait

parameters and an upper extremity joint kinetics. Following informed consent, data

were collected for nine children with spastic, diplegic cerebral palsy who were

community ambulators and who routinely used posterior walkers. Results of the study

showed increased double limb support time (24.3 -30.7 ) with the anterior walker,

increased walking speed (16.7 -21.4 ) with the posterio r walker. Elbow extensor and

wrist flexor demands were greater with the anterior walker (-0.19 “/ kg , 0.07 “/ kg )

than with the posterior walker (-0.06 “ k g , 0.02 “/kg ). The methodology developed

in this study appears to provide improved insight into the effect

of

upper extremity

muscular demands in addition to the traditional lower extremity gait analysis, clinical

evaluation, and energy expenditure assessment.

Keywords

upper extremity kinem atics, upper extremity kinetics, walker dynamom eter

1. Introduction

Impaired equilibrium reactions, balance, postural stability, and abnormal muscle tone are

chara cteristics of children with cereb ral palsy. Ambulation in these patien ts is

sometimes limited by these factors, and their mobility may be dependent upon the use of

assistive ambulatory devices, such as canes, crutches, or walkers. These aids afford

improved balance and theoretically fac ilitate the forward progression of gait. Thou gh

the literature contains information regarding the use of canes and crutches as assistive

devices and their biomechanics and determinants on gait, little quantitative data

is

availa ble on the effect of walkers on gait pattern s of childre n with cerebral palsy.

217

0-7803-6469-4/00/ 10.00

2000

IEEE



The selection of the type of walker, either anterior

or

posterior, is typically subjective,

based upon the observ ation of the child by the physician and/or therapist. This

observation is usually done in the clinic

or

at school or private therapist with little time

for adaptation. Objective data regarding parameters of gait, statiddynam ic stability,

load borne by the upper extrem ities, and efficienc y of gait are rarely determ ined.

Current studies do not address quantitative three-dimensional upper extremity kinem atics

or loads borne by the upper extremities. Small population sample sizes also limit

application of the findings. The purpose of this study was to obtain insight

in

children

with spastic cerebral palsy who use walkers to assist in their ambulation, comparing the

traditional front

or

anterior walker, with the newer posterior wa lker.

2. Methods

2.1

Subject Selection and Testing

Nine patients aged

8

to 17 ( p = l l years) with spastic cerebral palsy and a diplegic

distribution were studied using two-wheeled anterior and posterior walkers. Signed

informed consent was received from paren ts

or

guardians. They were first evaluated on

three separate occasions over a three week period while using their posterior walkers.

Evaluation consisted of com puter-assisted gait analysis and clinical exam ination. In the

gait analysis laboratory, the subjects were asked to walk on a 10 m walkway with an

instrumented walker. A minimum of

five

acceptable bilateral strides were collected for

analysis. Follow ing the initial three-test series, the subjects receive d training in the use

o an anterior walke r by a physical therapist. After succ essful com pletion of training, the

subjects used anterior walkers daily within their community environment

for

a period of

one month. The subjects then underwent another three-test series using the anterior

walker.

2.2 Walker Dynamometer

To study pediatric w alker-assisted gait, we modified a pediatric posterior w alker (Kaye

Model W3B, Kaye Products, Inc., Hillsborough, NC) and an anterior walker (Guardian

Products Model 7749, Sunrise Medical, Simi Valley, CA) to accept two 6 axis, strain

gage-based, load cells (AMTI Model MCW-6-500), in a cooperative effort with

Advanced Me chanical Technology, Inc. (AMTI, Watertown, MA), (Figures 1,2). The

results from our finite element study and prototype walker instrumentation were used to

position the load cells

so

that the forces and mom ents generated at each hand could be

accurately detected

[ l ]

[2] [3].

The system was lightweight, with each load cell

weighing about 100 grams and were cylindrical in shape with a diam eter of

38 mm

and

height

of 60

mm. The load cells were tethered to two AMTI orce plate amplifiers

(Model OR6-5).

The manufacturer-supplied primary sensitivities

in

units of mV /N(cm ). Sensitivities

were m aximum in the anterior-posterior Fx loading direction and minimum in the

vertical Fz loading direction. The specified non-linearity and hysteresis of the loads

cells were less than +0.20 . The lowest resonant frequency of a stand-alone cell was

700

Hz. Based on preliminary data collection, system gains of 4000 were set for the

218



vertical force channels and gains of 2000 were selected for the anterior-posterior and

medial-lateral force channels. Gains of 1000 were set for all mom ents.. Mornen ts

applied by the hands were uniquely determined by subtracting from the recorded

moment signals the product of applied force and distance from the transducer center to

the point of force application.

Figure 1. Posterior Walker Dynamometer

Figure 2. Anterior Walker Dynamometer

219



2.3

Upper Extremity Biomechanical Model

A biomechanical model to calculate sagittal, coronal, and transverse kinetics of the

shoulder, elbow, and wrist joints was developed

[l].

The upper body segments are

modeled as rigid links connected by idealized joints located at stationary, estimated

centers-of-rotation. The coordinates of external passive reflective markers are used to

determine flexiodextension (sagittal), abductiodadduction (coronal), and

internal/external (transverse) rotations of the upper body using a multi-segment rigid

body model similar to that used by K adaba, et al. [4] (Figure

3) .

Complete joint motion

is described with three sequence-de pendent Euler angles. The loading of the upper body

joints (w rist, elbow, and shoulde r) was determined using an inverse dynam ics model.

Upper Body Kinematic Model

Place external reflective markers

over anatomical andmarks

Estimate nternal oint centers ron

markers and anthropometric

relationships

Construct local

body

reference

frames using vector methods

Calculate relative oint angles

using Euler angle theory

Upper Body KiLetic Model

An Inverse Dynamics

model i ncorporating

measured with the

walker dynamometer

Angular and l inear

Figure 3. Represen tation of Upper Body Kinematic and Kinetic Models

3 Results

3.1

Gait Metrics

Double stance time w ith anterior walker use was significantly greater than with posterior

walker use (p=0.0004) for both the left and right sides. Mean do uble limb support time

increased 24.3 30.7 with the anterior walker compare d to the posterior walker.

Walking speed with posterior walker use was significantly greater than for anterior

walker use (p=O.OOOl) for both the left and right sides. Mean increases in speed were

16.7%

21.4 with the posterior walker. This was accom plished by significant

increases

in

cadence

(7.9%

9.6%)

and

in

stride length

(6.1%

-7.6 ).

3.2 Upper Extremity Kinematics

Figure 4 illustrates the mean trunk and elbow sagittal plane joint angles when walking

with the anterior and posterior walkers. Group means were plotted at discrete

increments of the gait cycle (IO , 30 , 50 , 70 ,

90%).

The right side upper

extremity kinematics were graphed with respect to the right foot stride (rfc, rfo, rfc) and

similarly the left side upper extremity kinematics were graphed with respect to the left

foot stride (lfc, Ifo, lfc).

220



trunk

left elbow

X

ait cycle

right elbow

I,

20 4

60

60

X

ait cycle

Figure

4.

Mean sagittal plane upper extremity kinematics for walking with an

anterior and posterior pediatric walker. N=9 subjects with spastic,

diplegic cerebral palsy,

n= 5

per subject, per walker. Flexion

(+)/extension

(-).

Trunk flexiodex tension did not differ significantly between the two walkers. Changes in

the trunk angle ranged from

0.0

o

2.1 .

The shoulder was significantly more extended

(12.9

19.9 )

with posterio r walker use than with anterior walker use. Increa ses

in

elbow flexion with the anterior walker ranged from

1.3

to

7.2

and were statistically

significant throughout the gait cycle on the non-dominant side.

No

significant

differences in wrist extension were determined for use of the two walkers.

22

1



3 2 Upper Extremity Kinetics

A

net demand on the shoulder flexors

(0.15

“ /k g ) was noted with posterior walker use

while a net extensor demand

(-0.04

“ k g ) was seen with anterior walker use. Elbow

extensor demands were greater with anterior walker use

(-0.19

”/ kg ) than with

posterior walker use (-0.06 “ /k g ) and the differences were statistically significant

throughout the gait cycle on the non-dom inant side. Significantly greater demands on

the wrist flexors were noted when walking with the anterior walker (0.07 “ k g ) than

with the posterior walker

(0.02

“ / k g ) .

Separate trials of hand-to-walker loading for subject ER are shown

in

Figure 5. For this

subject as well as the others, a posteriorly directed shear force (-Fx) was observed du ring

late stance to swing phase when using the anterior walker. In contrast, an anteriorly

directed shear force (+Fx) was noted throughout the gait cycle when using the posterior

walker. Hand-to-w alker vertical forces and mome nts applied in the sagittal plane were

similar

in

magnitude and morphology for both walkers.

Hand-to-Walker Force

Fx

Posterio r Walker

(+)

direction of

walk

Hand-to-Walker Force

Fx

Anterior Walker

(+)

direction of walk

W

30 30

30 30

60

60

gait cycle gait cycle

Figure

5.

Subject ER sagittal plane hand-to-w alker loads for walking with an anterior

and posterior walker.

4. Discussion

The purpose of this study was to initiate a quantitative comparison of ambulation with

anterior and posterior w alkers in children with spastic, diplegic cerebral palsy.

The walker dynamometer allowed measurement of three-dimensional wrist, elbow and

shoulder loads in children and quantitative biomechanical comparison of anterior and

posterior walker usage. Th e system was designed for use within a standard gait analysis

laboratory and

has proven to be accurate and reliable during preliminary trials. Th e

system is considered appropriate for further clinical application and for analysis of

therapeutic surgical and non-surgical treatment.



A limitation to this study is the small sample size of nine subjects. How ever, estimates

of parameter variance were used to project appropriate sample sizes for future study

design. For a sam ple size of thirty subjects, conservative estimates of the minimum

effect size which can be detected at the

5

significance level with 90 power are a

mean u pper extremity kinematic change of 6 degrees (3” trunk - 9” shoulder) and a mean

upper extremity kinetic chan ge of 0.07 “ / k g (0.04 “ / k g wr ist - 0 .10 “ /k g e lbow).

Potential rehabilitation applications which could benefit from this technology may

include the optimization of pediatric walker-assisted gait. In order to optimize the

function with walkers, we must first understand the details of motion and force transfer.

While it is well known that upper extremity work increases energy demands, the

relationship of energy expenditure to load distribution among the wrist, elbow, and

shoulder joints is not well understood. The walker dynamom eter and biomechanical

models would potentially allow design of a user-spec ific structure, optimized to retain

the determinants

of

gait, reduce internal moment demands, and improve efficiency.

Reference

[l] R.A. Bachschmidt, G.F.

Harris,

G.G. Simoneau, J.J. Wertsch.

“Analysis of

Walker-A ssisted Gait: Kinetics and Kinematics.”

IEEWEMBS s” Annual

Conference Chicago, IL pp.2851-2856, Oct 30-Nov 2, 1997.

[2] R.A. Bachschmidt, G.F. Harris, J.A. Ackman,

S .

Hassani

K. Reiners, W .

Olsson, F. Carignan, G. Blanchard. “De velopment of a System for Quantitative

Study of Pediatric Walker-A ssisted Gait.

IEEWEMBS C onference

Hong Kong

Oct. 1998.

[3] R A . Bachschm idt, G.F. Harris, J.A. Ackma n,

S .

Hassani K. Reiners, W . Olson.

“Walker-A ssisted Kinetics in Children with Spastic Cerebral Palsy: A

Preliminary Study.”

Proc

NASGCMA Dallas, TX, March 10-13, 1999;4.

[4] R.A. Bachschmidt, G.F. Harris, J.A. Ackman, S. Hassani, K. Reiners, W. Olson.

“Walker-Assisted Gait

in

Children with S pastic Cerebral Palsy.

Proc POSNA

Orlando, EL May 17-19 1999.

[ 5 ] M.P. K adaba, H.K. Ram akrishnan, M.E. Wooten. Measurem ent of low er

extremity kinematics during level walking. J Orthop

Res

8:383-392;1990.

223

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Quantitative Study of Walker-Assisted Gait in Children With Celebral Palsy

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