Measurement of Wire Deflection on Loading may Indicate Union in Ilizarov Constructs: A Pilot Study

Introduction: No entirely reliable method to assess union during Ilizarov treatment exists. Premature frame removal results in treatment failure, and alternative methods of assessment warrant investigation. Wire deflection might provide an indication of fracture site deformation on weight-bearing, indicating progress towards union. A previous in vitro study from our group demonstrated this approach may be clinically applicable. We investigated translation of this method into clinical practice in an observational pilot study. Materials and methods: Patients with tibial shaft fractures treated with Ilizarov frames were recruited. A prototype depth gauge was used to measure wire deflection on weight-bearing. Investigators undertaking the measurement were blinded to the clinical stage of treatment, and clinicians caring for the patient were blinded to deflection results. Patient records were reviewed at the end of treatment to determine likely fracture stability at each time point. Deflection per kg of weight applied, per mm from the ring was compared between stable and unstable situations. Results: Thirty-one measurements were obtained in 14 patients. The situation was deemed stable at 13 and unstable at 18 measurements. The median deflection in the stable group was 0.030 microns/kg/mm (IQR 0.005–0.104) and 0.165 microns/kg/mm (IQR 0.072–0.328) in the unstable group. This difference was statistically significant (Wilcoxon Mann–Whitney test p = 0.0014). ROC curve analysis revealed that wire deflection was able to predict clinical stability (AUC 0.84, p <0.0001). Various technical problems were encountered when using the device which would potentially limit its clinical utility in its current form. Conclusion: In this set of observations, wire deflection was significantly associated with clinically and radiologically determined stability. Though various practical limitations were encountered in using the prototype measurement device, this proof-of-concept study supports further development of this approach. The research group plan to develop a smaller, more reliable device for further clinical testing in a larger group of patients.