Ultrasonography of postosteotomy "cysts".

Three patients with postosteotomy "cysts" complicating limb-lengthening procedures are described. In all of the patients serial radiographs after distraction failed to show new bone formation, but the cause of the delay was not obvious from these images. Ultrasonography (US) revealed a well-defined fluid collection as the factor responsible for delayed consolidation. In one of the patients the fluid collection recurred, in spite of several attempts at US-guided percutaneous aspiration. In all three patients compression of the bone ends followed by redistraction failed to yield any new bone at the distraction site. Two of the patients subsequently underwent bone grafting at the site of osteotomy. Postosteotomy "cysts" (which are not true cysts) constitute an avoidable complication of distraction osteotomy resulting from inadequately supervised or too-rapid distraction. US is the imaging modality of choice for early detection of this complication.