Sonographic evaluation of bone production at the distraction site in Ilizarov limb-lengthening procedures

The success of the Ilizarov distraction technique has resulted in a marked increase in the number of limb-lengthening and limb-straightening procedures performed for the correction of short and deformed limbs. This technique involves fracture of the bone and application of an external ring and bar support frame with circumferential screw threads and nuts, which allows systematic distraction of bone segments at a rate of 0.25 mm four times a day. During the procedure, the patient is encouraged to be ambulatory, as the strength of the frame allows weight bearing. Because of the limitations of plain radiographs in detecting the small amounts of new bone formation that occur at the distraction site in the early stages of healing, the success of the procedure cannot be determined for many weeks. The rate of distraction depends on the successful production of new bone in the distraction site. Early evaluation of new bone production is therefore important, because slow bone formation requires a decrease in distraction rate and vice versa. We examined 12 patients who had limb-lengthening procedures via the Ilizarov technique to determine if sonography could be used to detect early new bone formation at the distraction site. Our results show that new bone formation could be detected with sonography many weeks before its appearance on the radiograph. The sonographic appearance of new bone consists of echogenic foci within the distraction site, which become aligned in the longitudinal plane and which increase in number and size until they coalesce as echodense bone, which does not allow through-transmission of the ultrasound beam. In addition, sonograms showed 1.5-cm and 2-cm cysts within the distraction site in two patients in whom they were not visible on the radiographs. Timely percutaneous aspiration allowed continued normal bone generation. We conclude that sonography is useful for the detection of new bone formation at the distraction site in patients undergoing the Ilizarov procedure.