The use of mandibular body distraction in hemifacial microsomia
A 12-year-old girl presented with grade IIb right-sided hemifacial microsomia. She had already undergone right ear reconstruction for microtia and maxillary driven simultaneous maxillomandibular distraction[] [].\nWe initially performed a computer-simulated surgery using image processing software (Mimics, Materialise NV, Leuven, Belgium) and a substance model (Kezulex, Ono and Co., Ltd, Tokyo, Japan) as a preoperative simulation. We planned the osteotomy lines to avoid damaging the nerve pathway. The simulation of surgery indicated that mandibular body on the affected side should be distracted 15 mm to the anterior and 10 mm inferiorly to improve facial symmetry. We proceeded with the surgery based on simulation [].\nThe procedure was performed under general anesthesia with nasotracheal intubation. Incisions were made along the mandibular rim and at the base of gingivolabial groove of canine tooth on right side to canine tooth on left side. Mucoperiosteal detachment was performed from the chin region to mandibular body while avoiding damage to mentonian nerve. The muscle insertion on the mandible's internal cortical bone was preserved to ensure vascularization of osteotomized segment, thus retaining effective traction of genioglossus muscle.\nFollowing these incisions, an osteotomy was performed according to preoperative simulation. Thereafter, two sets of the three-dimensional NAVID system were fixed to ramus and free mandible on the affected side. The front of the system was equipped with a distraction vector in inferior direction, and the rear of the system was equipped with a distraction vector in anterior direction []. The rods of the system were inserted through a small skin incision at the mentum, and hinge plate was attached on unaffected side and served as a pivot point for rotation. The wound was then closed.\nAfter 7 days, the distraction was initiated at a rate of 1 mm per day. This process was continued until desired clinical endpoints were achieved; the process is summarized in . As the distraction continued, there was a change in the angle at which two devices crossed and free mandible extended towards the anterior direction and inferiorly because neck of NAVID system could move in three dimensions. Towards the end of distraction period, we performed a 15 mm distraction with frontal device and a 22 mm distraction with rear device.\nWhen the distraction was completed, externally exposed rods were cut in very close proximity to the skin. After a 3-month consolidation period, the devices were removed under general anesthesia. Both the intraoperative view and preoperative computed tomography (CT) image indicated presence of osteogenesis, and showed a symmetrical improvement of mandibular contour compared with preoperative profile [].