title: Axial stiffness and ring deformation of complete and incomplete single ring circular external skeletal fixator constructs.
abstract: OBJECTIVE
  To compare the axial stiffness, maximum axial displacement, and ring deformation during axial loading of single complete and incomplete circular (ring) external skeletal fixator constructs.
  
  
  METHODS
  32 groups of single ring constructs (5 constructs/group).
  
  
  METHODS
  Single ring constructs assembled with 2 divergent 1.6-mm-diameter Kirschner wires were used to stabilize a 60-mm-long segment of 16-mm-diameter acetyl resin rod. Construct variables included ring type (complete or incomplete), ring diameter (50, 66, 84, or 118 mm), and fixation wire tension (0, 30, 60, or 90 kg). Axial loading was performed with a materials testing system. Construct secant stiffness and maximum displacement were calculated from the load-displacement curves generated for each construct. Ring deformation was calculated by comparing ring diameter during and after construct loading to ring diameter prior to testing.
  
  
  RESULTS
  Complete ring constructs had greater axial stiffness than did the 66-, 84-, and 118-mm-diameter incomplete ring constructs. As fixation wire tension increased, construct stiffness increased in the 66-, 84-, and 118-mm-diameter incomplete ring constructs. Maximum axial displacement decreased with increasing fixation wire tension, and complete ring constructs allowed less displacement than did incomplete ring constructs. Incomplete rings were deformed by wire tensioning and construct loading.
  
  
  CONCLUSIONS
  Mechanical performance of the 66-, 84-, and 118-mm-diameter incomplete ring constructs improved when wire tension was applied, but these constructs were not as stiff as and allowed greater displacement than did complete ring constructs of comparable diameter. For clinical practice, tensioning the wires placed on 84- and 118-mm-diameter incomplete rings to 60 kg is recommended.
authors.affiliation: Comparative Orthopaedic and Biomechanics Laboratory, University of Florida, Gainesville, FL 32610, USA. HudsonC@ufl.edu
authors.forename: Caleb C
authors.initials: CC
authors.lastname: Hudson
authors.forename: Daniel D
authors.initials: DD
authors.lastname: Lewis
authors.forename: Alan R
authors.initials: AR
authors.lastname: Cross
authors.forename: MaryBeth
authors.initials: M
authors.lastname: Horodyski
authors.forename: Scott A
authors.initials: SA
authors.lastname: Banks
authors.forename: Antonio
authors.initials: A
authors.lastname: Pozzi
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001864:Bone Wires / Q000662:veterinary; D002415:Cats; D004285:Dogs; D004867:Equipment Design / Q000295:instrumentation / Q000379:methods / Q000662:veterinary; D016267:External Fixators / Q000592:standards* / Q000662:veterinary; D005592:Fracture Fixation / Q000592:standards* / Q000662:veterinary