Bone healing of an unfixed bone fragment of the distal segment in sagittal split ramus osteotomy

In bilateral sagittal split ramus osteotomy for the correction of asymmetry of the mandible, yawing movement of the distal segment can displace the proximal segment. This displacement can be minimized through osteotomy of the posterior part of the distal segment (ie, distal cutting). This free bone fragment is usually removed because of the difficulty of fixation. No previous studies have examined whether union of the bone fragment after distal cutting could join and consequently strengthen the thinned mandibular posterior border. This study used CT imaging to evaluate bone union of the unfixed bone fragment at 3 months postoperatively. The location of the bone fragment and the morphology of bone healing were evaluated in 2D and 3D. The amount of cancellous bone healing between the free bone segment and the proximal segment averaged 63.69%. There was no correlation between the size of the bone gap and the degree of bone union. In most cases, the free bone fragment was located between the distal and proximal segments and tended to dislocate in an anterior-superior direction. Because the postoperative follow-up period was only 3 months, a longer-term study of the changes in bone volume after remodeling is necessary.