DUAL ENERGY X-RAY ABSORPTIOMETRY IN ILIZAROV LENGTHENING PRIOR TO REMOVAL OF THE FIXATOR

Abstract

Purpose: The goal of this study was to evaluate the use of dual energy x-ray absorptiometry (DEXA) to subjectively assess distraction osteogenesis callous regenerate strength to aid in the determination of when to remove the external fixator device in patients undergoing distraction osteogenesis for limb length discrepancies.

Methods: All patients that underwent distraction osteogenesis with either an Ilizarov or Orthofix frame from 1984 to 2005 at the Montréal Shriners Hospital Canada that had monthly DEXA scans prior to removal of their external fixators were included. The fixators were removed once two consecutive DEXA scans showed that the bone mineral density (BMD) had plateaued with a less than 10% successive increase in BMD. A retrospective chart and radiographical review was performed to assess the healing index and post fixator removal complications.

Results: 30 patients underwent 32 corrections. There were 29 lengthenings and 3 lengthenings with angular corrections. The average lengthening was 5.4 cm (3.6–9.1). The healing index average was 49 days/cm (20–77). All patients were progressed from partial to full weightbearing within 6 weeks of fixator removal. There were 2 post removal fractures. One patient fractured through the regenerate and another fractured through a proximal pin site.

Conclusions: Current methods of assessing distraction osteogenesis callous prior to removal of fixator are objective methods based on plain radiographs that have been shown to have poor interobserver reliability. Fractures occurring after fixator removal range between 10–15%. Using DEXA to determine when the regenerate bone mineral density and thus bone strength has plateaued yielded a post fixator removal regenerate fracture rate of 3% in our review. This new method of subjectively assessing the regenerate as compared to other objective radiological methods is a reliable alternative that safely predicts when to remove the fixator with a low post removal fracture rate while maintaining an acceptable bone healing index.