Yielding of the clamped-wire system in the Ilizarov external fixator

Abstract

This study demonstrates that the clamped-wire system used to suspend bones within an Ilizarov external fixator yields when the perpendicular load exceeds 50 N per wire. Cyclic loading was applied to tensioned wires clamped within an Ilizarov ring component, with steadily increasing load amplitude. Wires were tested at four initial tension settings. The amount of energy lost within the clamped-wire system per load cycle was calculated for every test. The results showed that there was a consistent trend to increasing non-recoverable energy loss per load cycle when peak loads exceed 50 N for all initial tension settings. A finite element (FE) model replicating the experimental conditions was performed to investigate the levels of stress within the loaded wires. The FE model analyses showed that high stresses were generated in the wires close to the clamping sites, and that the stress levels could reasonably be expected to exceed the material yield stress when loaded to about 55 N, for all initial tension settings. The results show that material yield, accompanied by some wire slippage through the clamps, is responsible for system yield, in agreement with previous studies. Although the initial wire tension has an appreciable effect on the wire stiffness, it did not affect the elastic load range of the clamped-wire system. To prevent yield of the clamped-wire system in practice, the fixator should be assembled with sufficient wires to ensure that the load transmitted to each wire by the patient does not exceed 50 N.

Rapid pre-tension loss in the Ilizarov external fixator: An in vitro study

“…Some authors believe that slippage is responsible for the loss of pre-tension (Aronson andHarp 1992, Renard et al 2005), while others have shown that material yield (Hillard et al 1998) or a combination of material yield and wire slippage (Delprete and Gola 1993, Watson et al 2003b, Osei et al 2006 cause the loss of pre-tension in the wires.…”

Analytical modelling of Kirschner wires in Ilizarov circular external fixator as pretensioned slender beams

“…Thus, the FEA in the present study can be used to verify the analytical solutions as given in §3. Watson et al (2000Watson et al ( , 2003b have published the results from their experimental work for displacements of a K-wire (DZ180 mm and dZ1.8 mm) loaded perpendicular to its longitudinal axis at its midpoint, under different pretensions, in two graphs ( fig. 5 of Watson et al 2000Watson et al , 2003b.…”

“…Watson et al (2000Watson et al ( , 2003b have published the results from their experimental work for displacements of a K-wire (DZ180 mm and dZ1.8 mm) loaded perpendicular to its longitudinal axis at its midpoint, under different pretensions, in two graphs ( fig. 5 of Watson et al 2000Watson et al , 2003b. The results in figure 8 of this paper, which are based on the analytical solutions, are comparable with the results shown in either of those graphs.…”

The effect of wire plane tilt and olive wires on proximal tibia fracture fragment stability and fracture site motion

“…The compression load was increased from 0 to 100 N at a rate of 10.0 N/s for each test. Loads were kept at relatively low levels to avoid yielding of the tensioned thin wire fixation based on the results of a study that showed the maximum sustainable transverse wire load before clamp yielding was 50 N per wire (Watson et al, 2003) and to simulate the early controlled loading associated with rehabilitation. The proximal load plate offset the medial and posterior loading by 4 cm and posteromedial loading was offset by 5.7 cm.…”