Distraction osteogenesis of the mandible: evaluation of callus distraction using the B-scan ultrasonography

Success with elongating the maxillofacial bones by means of distraction osteogenesis is often achieved by following a few main principles. International experience has illustrated that bone formation inside the distracted gap is ensured by preserving the periosteum supply, by not exceeding the timing of the elongation, and ensuring the correct period of stability given by the device itself to the distracted segment. The age of the patient, the type and quality of the bone undergoing distraction, the size of the osteotomy as well as the final length of the distraction gap, are all factors that easily make the osteogenesis process unpredictable. Because of this, it is mandatory to find a repeatable, easily managed diagnostic system that can describe this dynamic process. The authors report their experience in the development of a new protocol for monitoring the distraction osteogenesis of the mandible using B-scan imaging. Comparison with traditional radiological methods was performed in 12 different cases of mandibular distraction osteogenesis and then analysing the information obtained. All patients underwent distraction osteogenesis by means of an intraoral distraction device. The distraction protocol included: a latency period from 5 to 7 days; a distraction rate of 0,5 to 1.0 mm once a day and a stabilization period of 8 to 16 weeks. The radiological protocol consisted of using X-ray imaging and B-scan imaging at the following times: start, middle and end of the stabilization phase. Both evaluations were performed on the same day. Results are reported. X-rays were useful after surgery and during the active distraction phase to confirm the location of the device, its fixation to the bone, the presence of any broken parts, as well as the position of the distracted bone segments. X-rays were not able to evaluate the initial active process of bone formation, while B-scan ultrasonography appeared as a valid alternative to overcome this limitation. B-scan imaging made it possible to obtain defined and repeatable information about bone growth inside the distraction gap from the beginning to the formation of the new cortical layer. Direction, rate and quality of the osteogenetic process were precisely monitored. This accuracy of information given by the B-scan images was confirmed by histological evaluations performed at the time of the device removal. Soft tissue complications were also easily detected for example: swelling, hematoma, soft tissue damage and inflammatory reaction. Analysis of the results confirmed that in the follow up of distraction osteogenesis, X-ray examination is necessary immediately after surgery and during the active distraction phase. On the other hand, during the stabilization period, ultrasound plays a relevant role in monitoring the distraction osteogenesis process as well as the extra components of the maxillo-mandibular complex. After this study, it is author's opinion that B-scan imaging can be considered a radiological examination to be associated with conventional radiological procedures in the follow-up of the distraction protocol.