Wire bending development and progression during Ilizarov system tibial lengthening in skeletally immature patients with achondroplasia

Background: Tensile strength develops on wires during distraction osteogenesis (DO) using the Ilizarov system. The increase of tensile strength can lead to bending of the wires. The purpose of this study was to investigate the development and progression of wire bending during tibial lengthening using the Ilizarov system. We also identified factors that contribute to wire bending. Methods: Seventy-two segments of 36 skeletally immature achondroplasia patients (mean age, 8.5 years; range, 5.1–14.4 years) with bilateral tibial lengthening with the Ilizarov system were included in this study. The wire bending was defined as cases with loss of linearity of the wire during DO. The average distance of proximal and distal wires to the adjacent ring throughout the entire DO was measured to determine the progression of wire bending. In addition, age, height, weight, initial tibial length, gain of length, amount of correction of angular deformity, distraction index, external fixation index, and healing index were investigated to identify potential contributors to wire bending. Wire-related complications, including wire breakage, were also assessed. Results: Wire bending increased in the distraction phase (p ​< ​0.001 ​at the proximal wire and p ​= ​0.001 ​at the distal wire), but it stopped increasing in the consolidation phase. In addition, the amount of proximal wire bending was significantly larger than that of the distal wire (p ​< ​0.001) throughout the follow-up period. A greater amount of length gain (p ​= ​0.026) and heavy weight (p ​= ​0.004) significantly contributed to the development of wire bending. Wire bending did not interfere with bone consolidation. Wire breakage occurred in eight cases. Conclusion: This study indicated that the wire bending, which represented tensile strength on the wire, changed during the course of the DO. In addition, the amount of lengthening and the patient's weight may contribute to the degree of the wire bending. The translational potential of this article: Because excessive wire bending could lead to wire-related pain or even wire breakage, it is necessary to finely check and reduce the tension of the wire during DO in particular case of heavy patients or patients undergoing large amount of lengthening. Nevertheless, in case of wire breakage, remove the broken wire or fix it using the additional small plate to the Ilizarov system.