Gait Symmetry in Subjects with Multiple Sclerosis

Stephanie Crenshaw, James Richards, Caralynne MillerDepartment of Health, Nutrition, and Exercise SciencesUniversity of DelawareAmerican College of Medicine 53rd Annual MeetingMay 31-June 3, 2006 Denver, Colorado

Purposes

1. To explain newly developed Symmetry Analysis Method

2. To apply Symmetry Analysis Method to Clinical Population of Subjects with Multiple Sclerosis

MULTIPLE SCLEROSIS

Disease of the CNS Characterized by

demyelinated areas/axon damage in brain and spinal cord

Damage interferes with nerve signals that control muscle coordination, strength, sensation, and vision

Signs and Symptoms

Vision disturbances Numbness/weakness Tingling/pain Dizziness Unsteady Gait Fatigue

Measure of Disease SeverityExpanded Disability Status Scale

The EDSS is based upon Neurological testing of Functional Systems (CNS areas regulating body functions): Pyramidal (Walking Ability) Cerebellar (Coordination) BrainStem (Speech and Swallowing) Sensory (Touch and Pain) Bowel and Bladder Visual Mental Other (includes any other Neurological

findings due to MS)

EDSS Steps 1.0-4.5 patients are fully

ambulatory Precise step number determined by FS score

Steps 5.0-9.5 defined by impairment to ambulation

Steps 6.0-7.0 need assistive device

Steps 7.5-9.5 Wheelchair-bound/bedridden

MS Gait Compared to healthy controls:

Decreased velocity, stride length, range of motion

As disease severity increases: Variability of 25 FTW, Stance phase percentage

increase Gait Speed, Stride Length, Stride Rate decrease

With increased fatigue, no change in

balance performance (Frzovic, 2000) gait speed (Morris, 2002) stride length (Morris, 2002) double limb support duration (Morris, 2002)

Velocity, Peak Knee Flexion, Ankle Power Generation Decreased (Crenshaw, in press)

Symmetry Symmetry measures often

used to assess populations with unilateral injuries/disabilities

MS lesions develop in a random pattern in

CNS are distributed unequally

between right and left hemispheres of the brain

MS subjects Unequal stance duration Unequal step length

http://mccoy.lib.siu.edu/projects/mgrey/pathology/brain/multiple_selerosis/

Symmetry

Definition: Both limbs are behaving identically

Measures of Symmetry Symmetry Index Symmetry Ratio Statistical Methods

Symmetry Index

SI when it = 0, the gait is symmetricalDifferences are reported against their average value. If a large asymmetry is present, the average value does not correctly reflect the performance of either limbRobinson RO, Herzog W, Nigg BM. Use of force platform variables to quantify the effects of chiropractic manipulation on gait symmetry. J Manipulative Physiol Ther 1987;10(4):172–6.

%100*)(5.0

)(

LR

LR

XX

XXSI

Symmetry Ratio

Limitations: relatively small asymmetry and a failure to provide info regarding location of asymmetry

Low sensitivity

Seliktar R, Mizrahi J. Some gait characteristics of below-knee amputees and their reflection on the ground reaction forces. Eng Med 1986;15(1):27–34.

%100*L

R

X

XSR

Statistical Measures of Symmetry Correlation Coefficients Principal Component Analysis Analysis of Variance

•Use single points or limited set of points•Do not analyze the entire waveform

Sadeghi H, et al. Symmetry and limb dominance in able-bodied gait: areview. Gait Posture 2000;12(1):34–45.Sadeghi H, Allard P, Duhaime M. Functional gait asymmetry in ablebodied subjects. Hum Movement Sci 1997;16:243–58.

New Method - Eigenvector Analysis The method proposed utilizes eigenvector

analysis to compare time-normalized right leg gait cycles to time-normalized left leg gait cycles.

Paired data points from the right and left waveforms are entered into an m row x n column matrix, where each pair of points is one of the m number of rows. Singular Value Decomposition (SVD) is then performed on this matrix to determine the principal and secondary eigenvectors.

Eigenvector Analysis

Use eigenvector analysis to determine Waveform Trend Similarity

Trend Similarity is defined as the ratio of the variance about the principle eigenvector to the variance along the principle eigenvector

Additional Symmetry Measures Range ratio quantifies the difference in

range of motion of each limb, and is calculated by dividing the range of motion of the right limb from that of the left limb.

Range offset, a measure of the differences in operating range of each limb, is calculated by subtracting the average of the right side waveform from the average of the left side waveform.

Trend Symmetry

Expressed as ratio of the variance about eigenvector to the variance along the eigenvectorTrend Symmetry: 5.17% Range Amplitude Ratio: 0.79, Range Offset:0

Range Amplitude Ratio

Expressed as a ratio of the range of motion of the left limb to that of the right limbRange Amplitude Ratio: 2.0 Trend Symmetry: 0.0, Range Offset: 19.45

Range Offset

Calculated by subtracting the average of the right side waveform from the average of the left side waveformRange Offset: 10.0 Trend Symmetry: 0.0, Range Amplitude Ratio: 1.0

Final Adjustments A second measure of symmetry examines the

phase relationship between waveforms. To do this, we calculated the trend similarity for the sagittal plane joint angle between the normalized right and left limb waveforms. Then, one waveform was phase-shifted in 1-percent increments (e.g. sample 100 becomes sample 1, sample 1 becomes sample 2…) and the trend similarity was recalculated for each shift. The phase shift was then determined by identifying the index at which the smallest value for trend similarity occurred. The minimum trend similarity values are also reported.

Methods - Subjects

13 with MS Age 44.4±10.6

years Height 167.0±8.7

cm Mass 79.1±20.1

kg EDSS average 3.5 (range 2.5-4.5)

8 Healthy Controls Age 40.9±9.6

years Height

167.4±14.6 cm Mass 72.6±14.2

kg

Methods – Data Collection

Data Collection: 8 Motion-Analysis Cameras

60 Hz 2 AMTI Force Plates

960 Hz 2 Gait Analysis Conditions

Fresh Fatigued

Methods – Data Analysis

Created Ensemble averages of 15 gait cycles sagittal plane kinematics for fresh and

fatigued conditions Calculated Symmetry values

Affected/Unaffected – MS subjects Left/Right – HC subjects

Hip, Knee, and Ankle values were summed to determine composite symmetry measures

Methods – Data Analysis (HC)

HIP KNEE ANKLE SUM Trend Symmetry 0.01 0.36 0.73 1.01 Range Amplitude Ratio 0.94 0.93 0.88 2.75 Range Offset -0.72 0.02 0.49 0.2

Methods – Data Analysis (MS Fresh)

HIP KNEE ANKLE SUM Trend Symmetry 0.23 2.55 6.93 9.71 Range Amplitude Ratio 1.31 1.14 0.65 3.1 Range Offset -4.48 1.49 1.34 -1.65

Methods – Data Analysis (MS Fatigued)

HIP KNEE ANKLE SUM Trend Symmetry 0.79 5.86 3.52 10.17 Range Amplitude Ratio 1.55 1.07 0.75 3.37 Range Offset -6.08 -0.39 1.39 -5.08

Methods – Statistics

One-tailed independent samples t-test Changes between fresh conditions of MS and

control subjects

One-tailed dependent samples t-test Changes between fresh and fatigued

conditions for MS subjects

Correlation EDSS and differences between fresh and

fatigued conditions

Results – MS vs. Control example

HC

MS

Results – MS and Controls

MS subjects generally more asymmetrical than controls

p<0.05

MS HC Trend Symmetry * 3.6 ± 2.6 1.1 ± 0.5 Range Amplitude Ratio 3.1 ± 0.3 3.0 ± 0.2 Range Offset -1.1 ± 5.7 -1.6 ± 4.9 Phase Shift * 2.7 ± 1.6 1.3 ± 0.5 Adjusted Trend Symmetry * 2.6 ± 2.2 0.8 ± 0.5

Results – Fresh vs. Fatigued example

Fresh

Fatigued

Results – MS Fresh and Fatigued MS subjects generally become more

asymmetrical when fatigued

* p<.10

FRESH FATIGUED Trend Symmetry * 3.6 ± 2.6 4.6 ± 3.3 Range Amplitude Ratio * 3.1 ± 0.3 3.2 ± 0.3 Range Offset -1.1 ± 5.7 -0.8 ± 6.4 Phase Shift * 2.7 ± 1.6 3.5 ± 2.7 Adjusted Trend Symmetry 2.6 ± 2.2 3.0 ± 2.4

Results – Symmetry and EDSS

No significant correlations between disease severity and changes in symmetry from fresh to fatigued conditions

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Conclusions

MS subjects are less symmetrical than healthy control subjects

MS subjects generally become less symmetrical when fatigued

There was no significant correlation between disease severity and changes in symmetry measures from fresh to fatigued conditions.

Ankle Joint

Trend Symmetry

Phase Shift (% Cycle

Min Trend Symmetry

Range Amplitude

Range Offset

95% CI 0 – 6.30 -2.2 – 2.6 0 – 4.94 0.70 - 1.27

-6.8 – 6.2

Unbraced 0.94 1 1.37 0.89 3.8

Braced 29.01 -3 24.76 1.72 -5.6

Amputee 17.56 0 17.56 1.30 -3.7

Symmetry Example…Ankle Joint