1. Comparison of Fatigue Life for Three Types of Manual Wheelchairs Shirley Fitzgerald, PhD Rory Cooper, PhD Andrew Rentschler, BS Michael Boninger, MD Departments of Rehabilitation Science & Technology; Physical Medicine & Rehab; Bioengineering University of Pittsburgh VA Pittsburgh Healthcare System

2. 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

3. 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

4. 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

5. Methods, continued Results from testing entered into database Statistical analysis: –Chi-squares –ANOVA –Survival curve for fatigue life

6. 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

7. Results 64 wheelchairs tested –23 depot –27 ultralight –14 lightweights Number of Class failures –Class I: 21 –Class II: 29 –Class III: 45

8. Results DepotLightweightUltralightp-value % failed within 200,000 ddc 95.784.644.0<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

9. Mean Number of Double-drum Cyclesand Curb Drops WheelchairMean cycles/dropsp-value Double Drum depot85,282< 0.001 lightweight161381 ultralight192,083 Curb Drop depot897< 0.001 lightweight5,225 ultralight6,099

10. Survival Curve Fatigue Life in Three Wheelchairs Types Lightweight Ultralight Depot Equivalent Drum Cycles Cumulative Survival 1.2 1.0.8.6.4.2 0.0 050000100000150000200000250000

11. Conclusion Ultralight wheelchairs were significantly different than both lightweight and depot wheelchairs: –Fatigue life –Frame material –Type of class failures

12. Conclusion, continued Results can influence the choice of a wheelchair for consumers Results can impact cost- effectiveness of manual wheelchairs

13. 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

14. The End Dr. Cooper: rcooper+@pitt.edurcooper+@pitt.edu Review this lecture