Comparison of Fatigue Life for Three Types of Manual Wheelchairs Shirley Fitzgerald, PhD Rory...
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Transcript of Comparison of Fatigue Life for Three Types of Manual Wheelchairs Shirley Fitzgerald, PhD Rory...
Comparison of Fatigue Life for Three Types of Manual
Wheelchairs
Shirley Fitzgerald, PhDRory Cooper, PhD
Andrew Rentschler, BSMichael Boninger, MD
Departments of Rehabilitation Science & Technology;
Physical Medicine & Rehab; Bioengineering
University of Pittsburgh
VA Pittsburgh Healthcare System
ISO Wheelchair Testing Standards for Fatigue Life
• 200,000 Double Drum Cycles
• 6,666 Curb-drop tester drops
• Estimated that 200,000 & 6,666 curb drops = 3 years of wheelchair use
Failure in Fatigue Testing
• Class I, II, & III Failures
A chair is considered to fail the ISO standard if:
• A class III failure occurs (chair is no longer
able to function)
-or-
• 3 or more Class I or II failures occur
Methods
• Three types of manual wheelchairs tested– Depot– Light– Ultralight
• Fatigue testing completed on 64 different chairs• Notations made of all class I, class II, and class III
failures • Data collected on type of material that wheelchair
was made from & whether a frame failure occurred
Methods, continued
• Results from testing entered into database
• Statistical analysis:– Chi-squares
– ANOVA
– Survival curve for fatigue life
Survival Curves
• Aimed at estimating probability of survival, death, or any other event that occurs over time in a particular group under surveillance for a particular outcome
• Three types of chairs were considered ‘groups’
• Outcome was failure of the wheelchair• Event = the number of equivalent drum
cycles (200,000) over time
Results
• 64 wheelchairs tested– 23 depot– 27 ultralight– 14 lightweights
• Number of Class failures– Class I: 21– Class II: 29– Class III: 45
ResultsDepot Lightweight Ultralight p-value
% failed within 200,000 ddc
95.7 84.6 44.0 <0.001
% with Class 1 Failures
28.6% 14.3% 57.1% 0.04
% with Class II Failures
37.9% 13.8% 48.3% 0.08
% with Class III Failures
48.9% 22.2% 28.9% 0.02
Mean Number of Double-drum Cyclesand Curb Drops
Wheelchair Mean cycles/drops p-value
Double Drum depot 85,282 < 0.001
lightweight 161381
ultralight 192,083
Curb Drop depot 897 < 0.001
lightweight 5,225
ultralight 6,099
Survival Curve
Fatigue Life in Three Wheelchairs Types
Lightweight
Ultralight
Depot
Equivalent Drum Cycles
Cum
ulat
ive
Sur
viva
l
1.2
1.0
.8
.6
.4
.2
0.00 50000 100000 150000 200000 250000
Conclusion
• Ultralight wheelchairs were significantly different than both lightweight and depot wheelchairs:– Fatigue life
– Frame material
– Type of class failures
Conclusion, continued
• Results can influence the choice of a wheelchair for consumers
• Results can impact cost-effectiveness of manual wheelchairs
Acknowledgements
This study was funded in part by:
• Paralyzed Veteran’s of America
• NIDRR RERC on Wheelchairs
• US Department of Veteran’s Affairs, Rehabilitation Research and Development Service