title: Axial and torsional stiffness of pediatric prosthetic feet.
abstract: BACKGROUND
  Prosthetic stiffness likely affects the walking biomechanics of toddlers and children with leg amputations, but the actual stiffness values for prostheses are not reported by manufacturers or in standardized testing procedures.
  
  
  OBJECTIVE
  We measured axial (kA) and torsional (kT) stiffness from four brands of pediatric prosthetic feet (Trulife, Kingsley Mfg. Co., TRS Incorporated, and College Park Industries) over a range of foot sizes.
  
  
  METHODS
  We applied forces and torques onto prostheses with a materials testing machine that replicated those exhibited in vivo by using the kinetics measured from four non-amputee toddlers (2-3years) during walking.
  
  
  RESULTS
  Across brands, kAaveraged 35.2kN/m during heel loading, was more stiff during midfoot loading (121.8kN/m, P<0.001) and less stiff during forefoot loading (11.8kN/m, P=0.013). kAwas similar across brands with no statistically significant effect of prosthetic foot size, with the exception of the TRS feet. Plantarflexion torsional stiffness (kT1), was not statistically different across brands. For every 1cm increase in foot size, kT1increased 0.16kN·m/rad (P<0.001). College Park prostheses had 4.54kN·m/rad lower dorsiflexion torsional stiffness (kT2) (P<0.001) compared to other brands. For every 1cm increase in foot size, the kT2applied on the foot increased 0.63kN·m/rad.
  
  
  CONCLUSIONS
  The axial and torsional stiffness testing methods are reproducible and should be adopted by prosthetic foot manufacturers. Axial and torsional stiffness values of commercially available prosthetic feet should be publically reported to health practitioners to ensure evidence-based decisions and meet the specific needs of each patient with a leg amputation.
authors.affiliation: Department of Integrative Physiology, University of Colorado, Boulder, CO, United States. Electronic address: paolo.taboga@colorado.edu.
authors.forename: Paolo
authors.initials: P
authors.lastname: Taboga
authors.affiliation: Department of Integrative Physiology, University of Colorado, Boulder, CO, United States; Department of Veterans Affairs, Eastern Colorado Healthcare System, Denver, CO, United States.
authors.forename: Alena M
authors.initials: AM
authors.lastname: Grabowski
mesh_terms: D000671:Amputation, Surgical / Q000534:rehabilitation*; D001186:Artificial Limbs; D001696:Biomechanical Phenomena; D002675:Child, Preschool; D005260:Female; D005528:Foot / Q000502:physiology*; D005684:Gait / Q000502:physiology; D006365:Heel / Q000502:physiology; D006801:Humans; D008297:Male; D011474:Prosthesis Design; D013314:Stress, Mechanical; D016138:Walking / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology*
keywords: Ground reaction force; Mechanical testing; Pediatric prosthetic feet; Stiffness; Walking