title: Biomechanical and Cost Comparisons of Near-Far and Pin-Bar Constructs.
abstract: Orthopedic dogma states that external fixator stiffness is improved by placing 1 pin close to the fracture and 1 as distant as possible ("near-far"). This fixator construct is thought to be less expensive than placing pins a shorter distance apart and using "pin-bar" clamps that attach pins to outriggers. The authors therefore hypothesized that the near-far construct is stiffer and less expensive. They compared mechanical stiffness and costs of near-far and pin-bar constructs commonly used for temporary external fixation of femoral shaft fractures. Their testing model simulated femoral shaft fractures in damage control situations. Fourth-generation synthetic femora (n=18) were used. The near-far construct had 2 pins that were 106 mm apart, placed 25 mm from the gap on each side of the fracture. The pin-bar construct pins were 55 mm apart, placed 40 mm from the gap. Mechanical testing was performed on a material test system machine. Stiffness was determined in the linear portion of the load-displacement curve for both constructs in 4 modes: axial compression, torsional loading, frontal plane 3-point bending, and sagittal plane 3-point bending. Costs were determined from a 2012 price guide. Compared with the near-far construct, the pin-bar construct had stiffness increased by 58% in axial compression (P<.05) and by 52% in torsional loading (P<.05). The pin-bar construct increased cost by 11%. In contrast to the authors' hypothesis and existing orthopedic dogma, the near-far construct was less stiff than the pin-bar construct and was similarly priced. Use of the pin-bar construct is mechanically and economically reasonable. [Orthopedics. 2017; 40(2):e238-e241.].
authors.forename: Augusta
authors.initials: A
authors.lastname: Whitney Kluk
authors.forename: Tina
authors.initials: T
authors.lastname: Zhang
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Russell
authors.forename: Hyunchul
authors.initials: H
authors.lastname: Kim
authors.forename: Adam H
authors.initials: AH
authors.lastname: Hsieh
authors.forename: Robert V
authors.initials: RV
authors.lastname: O'Toole
mesh_terms: D001696:Biomechanical Phenomena; D001858:Bone Nails; D016267:External Fixators / Q000191:economics*; D005592:Fracture Fixation / Q000191:economics* / Q000379:methods; D050723:Fractures, Bone / Q000628:therapy*; D006801:Humans; D008422:Materials Testing