Assessment of bone formation in a porcine mandibular distraction wound by computed tomography

The purpose of this study was to document the progression of bone formation in a porcine mandibular distraction wound, at various distraction rates and fixation times, using three-dimensional computed tomography. Bone formation was assessed in a 0-day latency model (n=24 minipigs) using distraction rates of 1, 2, or 4 mm/day to create a 12 mm distraction gap. Animals were sacrificed at 0, 8, 16, or 24 days fixation. For experimental and control sides, three-dimensional data from computed tomographic scans were used to calculate the percent bone volume in the regions of interest. Standardized plain radiographs were used to evaluate bone formation with a semiquantitative scale: 0, 1, 2, 3. Mean percent bone volume and radiographic bone fill scores (pooled sample) increased with fixation time from 16.8% and 0.17 at 0 days, to 64% and 2.0 at 24 days fixation. Mandibles distracted at 1mm/day had higher CT values and bone fill scores than mandibles distracted at 2 or 4 mm/day. At 24 days fixation, the maximum percent bone volume (64%--1 mm/day; 24 days fixation) remained below control values (81.3%). The results of this study indicate that despite high bone fill scores on plain radiographs, the highest percent CT bone volume achieved in this model was 64%.