A CT SCAN TECHNIQUE FOR QUANTITATIVE VOLUMETRIC ASSESSMENT OF THE MANDIBLE AFTER DISTRACTION OSTEOGENESIS

Distraction osteogenesis has become an accepted method of treatment fo r patients requiring reconstruction of hypoplastic mandibles. We prese nt a quantitative analysis of volumetric changes after distraction ost eogenesis in a series of 10 patients. Group I (n = 5 patients, 3 unila teral craniofacial microsomia, 1 Goldenhaar syndrome, and 1 bilateral craniofacial microsomia) underwent unilateral distraction of the mandi ble. Group II (n = 5 patients, 1 Nager syndrome, 1 bilateral craniofac ial microsomia, 1 developmental micrognathia, and 2 Treacher Collins s yndrome) underwent bilateral distraction of the mandible. Predistracti on and postdistraction axial and three-dimensional computed tomographi c (CT) scans were digitized and transferred to a computer for analysis with image-processing software to determine the changes in volume of the mandible and bony regenerate. The CT-derived volume method was val idated by scanning three dry cadaver mandible specimens and comparing the volume data with those derived from a water-displacement method. T he difference between the two methods was less than 5 percent. The mea n distracted length, as recorded from the calibrated device, was 22.6 mm in the 10 patients. In the unilateral distraction group, the mean i ncrease in hemimandibular bone volume was 2.8 cc, with a mean percenta ge increase of 27 percent in the distracted hemimandible. In the bilat erally distracted patients, the mean increase in total mandibular volu me was 7.9 cc, with a mean percentage increase in bone volume of 25 pe rcent. This study represents the first attempt to quantify the increas e in bone volume resulting from distraction osteogenesis. Quantitative volumetric analysis of CT scans is an accurate method to measure the amount of bone regenerate in patients undergoing distraction osteogene sis of the mandible or the extremities. The concept and utility of qua ntifying the volumetric changes in bone following distraction osteogen esis may become more important as multiplanar devices are developed an d used in other areas of the craniofacial skeleton.