Embed Size (px)
Citation preview
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
