title: The influence of ankle-foot orthosis stiffness on walking performance in individuals with lower-limb impairments.
abstract: BACKGROUND
  Passive-dynamic ankle-foot orthoses utilize stiffness to improve gait performance through elastic energy storage and return. However, the influence of ankle-foot orthosis stiffness on gait performance has not been systematically investigated, largely due to the difficulty of manufacturing devices with precisely controlled stiffness levels. Additive manufacturing techniques such as selective laser sintering have been used to successfully manufacture ankle-foot orthoses with controlled stiffness levels. The purpose of this study was to use passive-dynamic ankle-foot orthoses manufactured with selective laser sintering to identify the influence of orthosis stiffness on walking performance in patients with lower-limb neuromuscular and musculoskeletal impairments.
  
  
  METHODS
  Thirteen subjects with unilateral impairments were enrolled in this study. For each subject, one passive-dynamic ankle-foot orthosis with stiffness equivalent to the subject's clinically prescribed carbon fiber orthosis, one 20% more compliant and one 20% more stiff, were manufactured using selective laser sintering. Three-dimensional kinematic and kinetic data and electromyographic data were collected from each subject while they walked overground with each orthosis at their self-selected velocity and a controlled velocity.
  
  
  RESULTS
  As the orthosis stiffness decreased, ankle range of motion and medial gastrocnemius activity increased while the knee became more extended throughout stance. Minimal changes in other kinematic, kinetic and electromyographic quantities were observed.
  
  
  CONCLUSIONS
  Subjects effectively compensated for changes in ankle-foot orthosis stiffness with altered gastrocnemius activity, and the stiffness levels analyzed in this study had a minimal effect on overall walking performance.
authors.affiliation: Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX 78712, USA.
authors.forename: Nicole G
authors.initials: NG
authors.lastname: Harper
authors.affiliation: Center for the Intrepid, Department of Orthopaedics and Rehabilitation, Brooke Army Medical Center, Ft. Sam Houston, TX 78234, USA.
authors.forename: Elizabeth Russell
authors.initials: ER
authors.lastname: Esposito
authors.affiliation: Center for the Intrepid, Department of Orthopaedics and Rehabilitation, Brooke Army Medical Center, Ft. Sam Houston, TX 78234, USA.
authors.forename: Jason M
authors.initials: JM
authors.lastname: Wilken
authors.affiliation: Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX 78712, USA. Electronic address: rneptune@mail.utexas.edu.
authors.forename: Richard R
authors.initials: RR
authors.lastname: Neptune
mesh_terms: D000328:Adult; D000842:Ankle / Q000502:physiology*; D000843:Ankle Joint; D001696:Biomechanical Phenomena; D004548:Elasticity; D005260:Female; D005528:Foot; D061826:Foot Orthoses; D005684:Gait / Q000502:physiology*; D020233:Gait Disorders, Neurologic / Q000534:rehabilitation*; D006801:Humans; D007719:Knee Joint; D008297:Male; D008875:Middle Aged; D008889:Military Personnel; D018482:Muscle, Skeletal / Q000473:pathology; D016059:Range of Motion, Articular; D016138:Walking / Q000502:physiology*
keywords: AFO; Biomechanics; Othosis; Selective laser sintering; Stiffness; Walking