Digital radiography. A predictor of regenerate bone stiffness in distraction osteogenesis

The newly formed regenerate bone during limb lengthening usually is assessed by observing standard plain radiographs. However, no objective data correlate the radiographic appearance with the quantitative strength of the newly formed bone. A noninvasive method was developed to assess the regenerate bone using digital radiography. The investigations were performed in a micropig animal model. The right tibia was distracted for 10 days at 2 mm per day. Digital radiography was performed after the distraction during a 10-day consolidation period. For quantitative analysis, an aluminum step wedge was placed on all images, and a region of interest was outlined in the regenerate bone. A calibration curve was calculated by measuring the corresponding gray values of the aluminum phantom. The calibration equation was used for determining the mean density in the region of interest. This method was sensitive in assessing day to day healing progress. The measurements taken the day before sacrifice were compared with torsional mechanical data using a material testing machine. The high correlation between the densimetric evaluations and the biomechanical data suggests this method is a useful tool for in vivo assessment of the regenerate bone during the consolidation period in distraction osteogenesis.