A biomechanical comparison of three hybrid linear-circular external fixator constructs
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Published on: October 9, 2014
Caleb C Hudson1, Daniel D Lewis, Alan R Cross
1Comparative Orthopaedics and Biomechanics Laboratory, University of Florida, Gainesville, FL 32610, USA. hudsonc@ufl.edu
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.
Study Design:
Biomechanical evaluation.
Sample Population:
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.
