The biomechanics of wire fixation in the Ilizarov system

The purpose of this study was to establish the optimal fixation of tensioned wires to the frame construct in the Ilizarov system. The usual torque to which the fixation bolts were tightened in clinical practice was established by serial testing of orthopaedic surgeons' work in our unit. The force required to produce wire slippage from the different types of wire fixation bolts, tightened to a predetermined torque, was measured using a testing rig. Analysis of the usual torque to which bolts were tightened in clinical practice, revealed values in the range of 5-10Nm. The load required to cause failure of the tensioned wire varied considerably depending on the bolt configuration used and the applied torque. In clinical practice, wires are tensioned using a dynamometer to a variety of loads, depending on the clinical situation, up to 1275N. In applying multiple wires across a single ring, as is normal practice, these loads may be increased still further. The total load transmitted by single wires in weightbearing may be up to 2000N. Utilising the results of our work has enabled us to choose, where practically possible, the optimal bolt configuration for wire fixation. In addition, this work has revealed that in order to withstand the loads seen in clinical practice, wire fixation bolts should be tightened to at least 10Nm. Post-operatively, we now tighten all our wire fixation bolts to 10Nm, using a calibrated torque wrench.