Clinical Implications from Rear Impact Investigations of a Wheelchair & Occupant

1. Clinical Implications from Rear Impact Investigations of a Wheelchair & Occupant Presenter: John Tiernan CEng1 Co-Authors: Jennifer Walsh2, Ciaran Simms2, David FitzPatrick3 Affiliations: 1. SeatTech, Enable Ireland 2. Trinity Centre for Bioengineering, Trinity College Dublin 3. School of Electrical, Electronic & Mechanical Engineering, University College Dublin

2. Research Background • Current recommended safety level – Wheelchair Tie-down and Occupant Restraint System (WTORS) • Main area of research - Frontal impact • Use of sled tests and numerical modelling has proven successful • Focus is on occupant retention • 50th percentile crash test dummy • ISO surrogate wheelchair

3. Representative Models - Occupant • Large variation among wheelchair occupants • Gender, age, height and weight influence the risk of injury (Temming et al1) • Current injury criteria based on general population; Level of risk associated with disabled population may be higher (Bertocci et al2) • Temming, J., Zobel, R. (1998) IRCOBI Conference Proceedings, Goteborg. • Bertocci, G. et al. (2000). IEEE Transactions on Rehabilitation Engineering 8(1): 126-39.

4. Representative Models - Wheelchair • Large Variety • Custom modifications to crash tested (ISO 7176-19) wheelchairs may nullify certification • Destructive testing unfeasible thus effect of alterations largely unknown Adapted Wheelchairs ISO Surrogate Wheelchair

5. Objectives of this Research… To investigate the effect of: • Rear Impact on an occupant and wheelchair during surface transport • Scoliosis in such an event • Adaptations to seating support surfaces on the predicted risk of injury

6. Methods • Sled testing of: • BioRID II occupant, and • Surrogate Wheelchair to provide validation data • Create and Validate a baseline Computational Model for Rear Impact • Used Model as an Analysis tool to investigate the effect of Seating Alterations

7. Crash Test (Thatcham) • IIWPG 10g rear impact • BioRID II • ISO surrogate wheelchair • WTORS

8. Validated Numerical Baseline Model • MADYMO Z X

9. Scoliosis Lateral Lateral Frontal Frontal

10. Scoliosis – Cobb Angle Frontal Lateral Mild Moderate Severe

11. Baseline Vs. Scoliosis Models Baseline Mild Scoliosis Moderate Scoliosis Severe Scoliosis

12. Altered Kinematics

13. Altered Kinematics

14. Point Loading Baseline Mild Scoliosis Moderate Scoliosis

15. Forces on Spine Peak force of 2.3kN in Thoracic region of Severe Scoliosis case approaches value that is known to damage Lumbar vertebrae, 2.8kN5 5. Begeman P. et al, SAE Technical Report 942205, 1994.

16. Apex of the Curve • Largest Force at the Apex of the deformed spine, caused by: • Largest deformity • Effect of point loading • In this area there is an associated • Rib hump • Respiratory problems6 6. Closkey R. et al, Journal of Orthopedic Research, 11(5):730-7, 1993.

17. Postural Supports Enable Ireland www.wheelchairnet.org

18. Addition of Postural Supports -using Planes

19. Addition of Cushioned Postural Supports Baseline wheelchair Adapted Wheelchair • Similar peak values of joint constraint force for moderate case of scoliosis in baseline & adapted wheelchair • Loading pattern is altered in adapted wheelchair, with large ramping up of forces

20. Bottoming out of cushion on the surface of postural supports

21. Addition of Rigid Postural Supports Baseline wheelchair Adapted Wheelchair • Peak values of force reduced • Effects of scoliosis are greatly reduced • Point loading is reduced due to larger contact area

22. Clinical Implications • Scoliotic occupant found to be at greater risk of injury • Seating adapted to fit the contours of an occupant provides an increased level of protection • Cushioning Material must be taken into account as the forces associated with a crash can lead to compression of a cushioning material & subsequent contact made with the harder surface beneath

23. Acknowledgements