Abstract
Aim
To investigate the biomechanical behaviours of the TL-Hex & Taylor Spatial Frame (TSF) Hexapod external fixators, with comparison to traditional ring-fixator constructs.
Methods
Standardised four-ring TL-Hex and TSF constructs, as well as matched ilizarov threaded-rod constructs for each set of components, were tested alone and mounted with an acrylic bone model with simulated fracture gap using fine-wires. Load-deformation properties for each construct and mode of loading were calculated and analysed statistically using ANOVA.
Results and Conclusions
Under axial loading the Ilizarov construct utilising TL-Hex components demonstrated greatest rigidity followed by the TL-Hex Ilizarov using TSF components (p<0.01). Under torsional loading both hexapod frames were seen to be significantly more rigid than the Ilizarov (p<0.01), with the TSF demonstrating greater rigidity than the TL-Hex. Under cantilever bending loads the difference in rigidity seen across all constructs was less marked. When loaded with the bone model both hexapods demonstrated reduced axial rigidity as compared to Ilizarov constructs, but without any appreciable difference in translational shear strain. Under cantilever bending the Ilizarov construct using TL-Hex components p<0.01) demonstrated less translational shear strain than the TSF and TSF using Ilizarov components. In conclusion, both hexapod designs were less rigid axially, but more so under bending and torsional loads, than their Ilizarov construct counterparts, producing greater overall planar shear strain, largely due to the observed “toe-in” laxity. Overall, the TL-Hex was seen to be more rigid that the TSF under bending loads although the difference in shear strain at the fracture site was not significantly different.
