title: A biomechanical comparison of three hybrid linear-circular external fixator constructs.
abstract: OBJECTIVE
  To evaluate the stiffness, displacement, ring deformation and bone model motion of 3 configuations of linear-circular hybrid fixator constructs loaded in axial compression, craniocaudal and mediolateral bending, and torsion.
  
  
  METHODS
  Biomechanical evaluation.
  
  
  METHODS
  Three hybrid construct configurations with 8 replicates/configuration.
  
  
  METHODS
  Construct Ia used a single, 84 mm, incomplete ring and 2 tensioned olive wires to stabilize 1 bone segment and a primary hybrid rod with 3 fixation pins to stabilize the other bone segment. Constructs Ia(d)  and Ib were similar to Ia with the addition of a secondary diagonal hybrid rod. Construct Ib had a fixation pin inserted orthogonally from the diagonal rod. Constructs were loaded for 10 cycles in each mode of loading using a materials testing machine. Ring deformation was assessed by obtaining serial ring measurements. Bone model motion at the fracture gap as a result of loading was also calculated.
  
  
  RESULTS
  Axial compression: constructs Ia(d)  and Ib were significantly stiffer than construct Ia. Craniocaudal bending: Construct Ib was significantly stiffer than construct Ia. Mediolateral bending: there were no significant differences between constructs. Torsion: Construct Ib was significantly stiffer than constructs Ia and Ia(d) . Permanent ring deformation did not occur. Bone model translational motion decreased in constructs Ia(d)  and Ib compared to construct Ia.
  
  
  CONCLUSIONS
  Addition of a secondary hybrid rod as well as biplanar fixation pin placement improved construct stiffness in several loading modes.
authors.affiliation: Comparative Orthopaedics 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: Nicholas J
authors.initials: NJ
authors.lastname: Dunbar
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: D001696:Biomechanical Phenomena; D004867:Equipment Design; D016267:External Fixators / Q000662:veterinary*; D005592:Fracture Fixation / Q000295:instrumentation* / Q000662:veterinary*; D008422:Materials Testing