[Ultrasound follow-up of callus distraction of the tibia. Technique, possibilities and limits].

In a prospective study 20 patients were monitored with serial sonograms and radiographs during distraction osteogenesis at the lower limb. All sonograms were obtained in four planes using a 7.5 MHz transducer. The distraction gap was seen as a sonolucent area in all patients after corticotomy. At an average of 20.7 (14-28) days after the beginning of the distraction, echogenic foci occurred and showed increasing longitudinal alignment with further distraction. Radiographical signs of beginning mineralization were seen an average of 48.3 days after the start of the distraction. Exact measurement of the distraction gap was possible in all patients during lengthening. Bone healing complications and hematoma could be detected by ultrasound. A rapid increase of bone mineralization was seen after the distraction was stopped. With increasing cortication of the regenerate bone, sonograms showed a hyper-reflecting solid line so that further mineralization and the time of removal of the fixator could not be assessed by ultrasound. Ultrasound is more sensitive than radiography in identifying new bone formation during distraction, measuring the length of the distraction gap, and detecting early bone-healing complications and can therefore reduce the need for radiographs.