Towards a solution of the wires' slippage problem of the Ilizarov external fixator

Clinical experience has indicated that many complications during treatment with the Ilizarov method, and mainly tract infection, are related to decreased wire tension. The aim of this work was to evaluate biomechanically a novel wire tensioning and clamping system that will minimise or even diminish the reduction of the wire pretension during treatment. The proposed approach is based on threading of the wire end in a sufficient length. The wire pretension is applied by twisting a nut on the threaded part of the wires against the ring and is recorded by an incorporated force sensor. For biomechanical evaluation, the frame, consisting of a polyethylene bar, simulating the bone fragment, suspended on two rings, was subjected to a dynamic load of 0-800 N at a frequency of 0.5 Hz. After dynamic loading for 20 min, loss of the initial wire pretension for the novel clamping system ranged between 12 and 16%. The average loss for conventionally clamped wires was 75%. The advantages of the novel clamping system were the much greater ability to sustain the transverse load and the easy and effectual wire re-tensioning. Although wire slippage has been avoided with the novel system, wire material yield is still responsible for a pretension loss.