# Comparison of Fatigue Life for Three Types of

• Slides: 14

Comparison of Fatigue Life for Three Types of Manual Wheelchairs Shirley Fitzgerald, Ph. D Rory Cooper, Ph. D Andrew Rentschler, BS Michael 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

Results Depot 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 lightweight 85, 282 161381 ultralight 192, 083 < 0. 001 Curb Drop depot lightweight ultralight 897 5, 225 6, 099 < 0. 001

Survival Curve Fatigue Life in Three Wheelchairs Types Cumulative Survival 1. 2 1. 0. 8. 6 Lightweight . 4 Ultralight . 2 0. 0 0 Depot 50000 100000 150000 200000 Equivalent Drum Cycles 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 costeffectiveness 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

The End • Dr. Cooper: [email protected] edu Review this lecture