Bar Diameter Is an Important Component of Knee-Spanning External Fixator Stiffness and Cost

The authors’ objective was to determine the effects of bar diameter on the stiffness and cost of a knee-spanning external fixator. The authors studied 2 versions of an external fixator with a difference in bar diameter (small bars, 8-mm diameter; large bars, 11-mm diameter). Fixators were tested using frame dimensions and a synthetic fracture model appropriate for a tibial plateau fracture. Five configurations of each fixator were tested: standard, cross-link, oblique pin, double stack, and super construct. The construct stiffness of each configuration (n=60) was measured in anterior-posterior bending, medial-lateral bending, axial torsion, and axial compression. Cost analysis allowed for calculation of the stiffness per unit cost. In the large bar group, an increase in construct stiffness was noted for all constructs and testing modes. Magnitude of stiffness increase ranged from 24% to 224% ( P