title: Biomechanics of the rhombic transposition flap.
abstract: OBJECTIVE
  To develop a computational model of cutaneous wound closures comparing variations of the rhombic transposition flap.
  
  
  METHODS
  A nonlinear hyperelastic finite element model of human skin was developed and used to assess flap biomechanics in simulated rhombic flap wound closures as flap geometric parameters were varied.
  
  
  METHODS
  In silico.
  
  
  METHODS
  The simulation incorporated variables of transposition angle, flap width, and tissue undermining. A 2-dimensional second-order Yeoh hyperelastic model was fit to published experimental skin data. Resultant stress and strain fields as well as local surface changes were evaluated.
  
  
  RESULTS
  For the rhombus defect, closure stress and strain were minimized for the transposition flap with a distal flap angle of 30° by recruiting skin from opposing sides of the defect. Alteration of defect dimensions showed that peak stress and principal strain were minimized with a square defect. Likelihood of a standing cutaneous deformity was driven by the magnitude of angle closure at the flap base. Manipulation of the transposition angle reoriented the primary skin strain vector. Asymmetric undermining decoupled wound closure tension from strain, with direct effects on boundary deformation.
  
  
  CONCLUSIONS
  The model demonstrates that flap width determines the degree of secondary tissue movement and impact on surrounding tissues. Transposition angle determines the orientation of maximal strain. Local flap design requires consideration of multiple factors apart from idealized biomechanics, including adjacent "immobile" structures, scar location, local skin thickness, and orientation of relaxed skin tension lines. Finite element models can be used to analyze local flap closures to optimize outcomes.
authors.affiliation: Naval Medical Center, San Diego, Department of Otolaryngology, San Diego, California, USA shelby.topp@med.navy.mil.
authors.forename: Shelby G
authors.initials: SG
authors.lastname: Topp
authors.affiliation: Exponent, Incorporated, Menlo Park, California, USA.
authors.forename: Scott
authors.initials: S
authors.lastname: Lovald
authors.affiliation: University of New Mexico Mechanical Engineering Department, Albuquerque, New Mexico, USA.
authors.forename: Tariq
authors.initials: T
authors.lastname: Khraishi
authors.affiliation: Naval Medical Center, San Diego, Department of Otolaryngology, San Diego, California, USA.
authors.forename: Curtis W
authors.initials: CW
authors.lastname: Gaball
mesh_terms: D001696:Biomechanical Phenomena; D003198:Computer Simulation; D020342:Finite Element Analysis; D006801:Humans; D008953:Models, Anatomic; D012822:Silicon Dioxide; D016038:Skin Transplantation / Q000379:methods*; D013524:Surgical Flaps; D013718:Tensile Strength; D058106:Wound Closure Techniques
chemical_list: D012822:Silicon Dioxide
keywords: cutaneous wound; finite element; hyperelastic; local flap; rhombic flap; skin flap; transposition flap; wound closure