title: Structural stiffness and reducibility of external fixators placed in malalignment and malrotation.
abstract: OBJECTIVE
  To determine the structural stiffness and reducibility of various external fixators placed in malalignment and malrotation.
  
  
  METHODS
  Uniform testing of all external fixator configurations.
  
  
  METHODS
  Orthopaedic biomechanical laboratory.
  
  
  METHODS
  Thirteen external fixators from different manufacturers, in a total of fifteen configurations, were studied. All external fixators were applied to a malreduction jig initially, and a subsequent anatomic reduction was then attempted. If an anatomic reduction was possible, the structural stiffness of those fixators was determined. If anatomic reduction was not possible, the external fixator was removed and reapplied to an anatomically reduced model, and then structural stiffness was determined.
  
  
  RESULTS
  Six of the thirteen external fixator configurations allowed an anatomic reduction after placement on a malreduction model. The other nine external fixator configurations would not allow for an anatomic reduction. All the external fixator configurations were biomechanically tested in anteroposterior bending, lateral bending, axial load, and torsion. Each fixator had its own structural stiffness and is reported.
  
  
  CONCLUSIONS
  Some external fixators will not allow for an anatomic reduction once placed in malalignment and malrotation without repositioning of the fixator pins. External fixator configurations (i.e., single-pin, dual-pin, and multipin barclamps) affect structural stiffness. Structural stiffness widely varied among the external fixators. Proper external fixator selection will enable early fracture immobilization in malalignment and malrotation in suboptimal conditions (e.g., wartime conditions or a civilian disaster), with subsequent external fixator adjustment for an anatomic reduction.
authors.affiliation: Department of Orthopaedic Surgery, Wilford Hall USAF Medical Center, Lackland Air Force Base, Texas 78236-53000, USA.
authors.forename: D B
authors.initials: DB
authors.lastname: Carmack
authors.forename: K L
authors.initials: KL
authors.lastname: Kaylor
authors.forename: M J
authors.initials: MJ
authors.lastname: Yaszemski
mesh_terms: D001696:Biomechanical Phenomena; D004638:Emergency Treatment / Q000295:instrumentation* / Q000379:methods; D004867:Equipment Design; D016267:External Fixators / Q000145:classification; D008422:Materials Testing; D019300:Medical Errors; D013978:Tibial Fractures / Q000628:therapy*; D013997:Time Factors