The mechanical test as a supplemental decision support tool for the safe removal of an Ilizarov circular external fixator.

Background: Timing the fixator removal is vital for a successful external fixation treatment. The purpose of this study was to determine the effectiveness of axial load-share ratio in vivo as a supplemental decision support tool for the safe removal of an Ilizarov circular external fixator.

Methods: This prospective observational study consists of 83 patients undergoing tibial or femoral lengthening with Ilizarov circular external fixation in our institution, from January 2011 to October 2019. In group I (38 patients), the external fixator was removed based on the surgeon's clinical experience and radiographs from January 2011 to June 2015. In group II (45 patients), from July 2015 to October 2019, the supplemental axial load-share (LS) ratio test was accomplished without the knowledge of the clinical results by another medical team. The test was performed by electronically measuring forces in the fixator rods and in a ground force plate. When the LS ratio < 10% was consistent with the conclusion (dense bone formation was achieved in the distraction zone) drawn from the corresponding routine radiographs by the treating surgeon, the external fixator was removed.

Results: There was no statistical significance in demographic data between the two groups (P > 0.05). In group I, 4 of the 38 patients suffered refracture (the refracture rate was 10.5%) after fixator removal, and bone union was finally achieved with further intervention by intramedullary nail. In group II, 36 patients terminated the external fixation after the first mechanical test, and another 9 patients terminated the external fixation at the subsequent test. None of the 45 patients in group II suffered refracture (the refracture rate was 0%). There was statistical significance in the refracture rate between the two groups (P < 0.05).

Conclusions: Adequate assessment of bone regenerate is crucial before removing an external fixator to prevent deformation or refracture. The axial load-share ratio in vivo is a practically quantitative method to supplement radiography and clinical experience for the assessment of regenerate healing, and the axial load-share ratio dropped below 10% is a safe limit for the Ilizarov circular external fixator removal.