title: The dynamics of electric powered wheelchair sideways tips and falls: experimental and computational analysis of impact forces and injury.
abstract: BACKGROUND
  To reduce the occurrence of wheelchair falls and to develop effective protection systems, we aimed to quantify sideways tip and fall dynamics of electric power wheelchairs (EPWs). We hypothesized that driving speed, curb height and angle of approach would affect impact forces and head injury risk for wheelchair riders. We further expected that fall dynamics and head injury risk would be greater for unrestrained riders compared to restrained riders.
  
  
  METHODS
  Sideways wheelchair tip and fall dynamics were reconstructed using a remotely operated rear wheel drive EPW and a Hybrid III test dummy driving at different approach angles (5 to 63°) over an adjustable height curb (0.30 to 0.41 m) at speeds of 0.6-1.5 m/s. Rigid body dynamics models (Madymo, TASS International, Livonia, MI) were developed in parallel with the experiments to systematically study and quantify the impact forces and the sideways tip or fall of an EPW user in different driving conditions.
  
  
  RESULTS
  Shallower approach angles (25°) (p < 0.05) and higher curbs (0.4 m) (p < 0.05) were the most significant predictors of tipping for restrained passengers. Unrestrained passengers were most affected by higher curbs (0.4 m) (p < 0.005) and fell forward from the upright wheelchair when the approach angle was 60°. Head impact forces were greater in unrestrained users (6181 ± 2372 N) than restrained users (1336 ± 827 N) (p = 0.00053). Unrestrained users had significantly greater head impact severities than restrained users (HIC = 610 ± 634 vs HIC = 29 ± 38, p = 0.00013) and several tip events resulted in HICs > 1000 (severe head injury) in unrestrained users.
  
  
  CONCLUSIONS
  Sideways tips and forward falls from wheelchairs were most sensitive to curb height and approach angle but were not affected by driving speed. Sideways tips and falls resulted in impact forces that could result in concussions or traumatic brain injury and require injury prevention strategies. Seat belts eliminated the risk of falling from an upright chair and reduced head impact forces in sideways wheelchair tips in this study; however, their use must be considered within the ethical and legal definitions of restraints.
authors.affiliation: School of Mechatronic Systems Engineering, Simon Fraser University, 250-13450 102 Ave., Surrey, BC, V3T 0A3, Canada. brette@sfu.ca.
authors.forename: Brett
authors.initials: B
authors.lastname: Erickson
authors.affiliation: School of Mechatronic Systems Engineering, Simon Fraser University, 250-13450 102 Ave., Surrey, BC, V3T 0A3, Canada. lukedmassey@gmail.com.
authors.forename: Masih A
authors.initials: MA
authors.lastname: Hosseini
authors.affiliation: School of Mechatronic Systems Engineering, Simon Fraser University, 250-13450 102 Ave., Surrey, BC, V3T 0A3, Canada. pmvanbc@gmail.com.
authors.forename: Parry Singh
authors.initials: PS
authors.lastname: Mudhar
authors.affiliation: MobiSafe Systems Inc., Room 5330 250-13450 102 Avenue, Surrey, BC, V3T 0A3, Canada. maryam7741@gmail.com.
authors.forename: Maryam
authors.initials: M
authors.lastname: Soleimani
authors.affiliation: MobiSafe Systems Inc., Room 5330 250-13450 102 Avenue, Surrey, BC, V3T 0A3, Canada. arinaaboonabi@gmail.com.
authors.forename: Arina
authors.initials: A
authors.lastname: Aboonabi
authors.affiliation: School of Mechatronic Systems Engineering, Simon Fraser University, 250-13450 102 Ave., Surrey, BC, V3T 0A3, Canada. arzanpour@sfu.ca.
authors.forename: Siamak
authors.initials: S
authors.lastname: Arzanpour
authors.affiliation: School of Mechatronic Systems Engineering, Simon Fraser University, 250-13450 102 Ave., Surrey, BC, V3T 0A3, Canada. csparrey@sfu.ca.|International Collaboration on Repair Discoveries (ICORD), Vancouver Coastal Health Research Institute and The University of British Columbia, Vancouver, BC, Canada. csparrey@sfu.ca.
authors.forename: Carolyn J
authors.initials: CJ
authors.lastname: Sparrey
mesh_terms: D000058:Accidental Falls; D000465:Algorithms; D003198:Computer Simulation; D006259:Craniocerebral Trauma / Q000209:etiology* / Q000503:physiopathology*; D006801:Humans; D008348:Manikins; D008953:Models, Anatomic; D012306:Risk; D012622:Seat Belts; D014910:Wheelchairs / Q000009:adverse effects*