title: Low-Cost Methodology for Skin Strain Measurement of a Flexed Biological Limb.
abstract: The purpose of this manuscript is to compute skin strain data from a flexed biological limb, using portable, inexpensive, and easily available resources.
  
  
  
  We apply and evaluate this approach on a person with bilateral transtibial amputations, imaging left and right residual limbs in extended and flexed knee postures. We map 3-D deformations to a flexed biological limb using freeware and a simple point-and-shoot camera. Mean principal strain, maximum shear strain, as well as lines of maximum, minimum, and nonextension are computed from 3-D digital models to inform directional mappings of the strain field for an unloaded residual limb.
  
  
  
  Peak tensile strains are ∼0.3 on the anterior surface of the knee in the proximal region of the patella, whereas peak compressive strains are ∼ -0.5 on the posterior surface of the knee. Peak maximum shear strains are ∼0.3 on the posterior surface of the knee. The accuracy and precision of this methodology are assessed for a ground-truth model. The mean point location distance is found to be 0.08 cm, and the overall standard deviation for point location difference vectors is 0.05 cm.
  
  
  
  This low-cost and mobile methodology may prove critical for applications such as the prosthetic socket interface where whole-limb skin strain data are required from patients in the field outside of traditional, large-scale clinical centers.
  
  
  
  Such data may inform the design of wearable technologies that directly interface with human skin.
authors.forename: Bevin
authors.initials: B
authors.lastname: Lin
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Moerman
authors.forename: Connor G
authors.initials: CG
authors.lastname: McMahan
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Pasch
authors.forename: Hugh M
authors.initials: HM
authors.lastname: Herr
mesh_terms: D000328:Adult; D000674:Amputees; D001186:Artificial Limbs; D001696:Biomechanical Phenomena / Q000502:physiology; D006801:Humans; D021621:Imaging, Three-Dimensional; D007717:Knee / Q000000981:diagnostic imaging / Q000502:physiology; D008297:Male; D016059:Range of Motion, Articular / Q000502:physiology*; D012867:Skin / Q000000981:diagnostic imaging*; D012879:Skin Physiological Phenomena