Introduction:  Significant asymmetric prognathism may be due to condylar hyperplasia or previous condylar trauma with growth disturbance. Mild asymmetric prognathism with class II malocclusion is much more common and the etiology is poorly understood. The traditional treatment to these deformities involve a two-jaw orthognathic correction with or without genioplasty. We investigated the etiology of this deformity with cranial analysis and compared the traditional treatment to a novel treatment using only a unilateral sagittal split mandibular osteotomy and final splint.

Methods:  In part I, we obtained preoperative New Tom scans and 3D photographic images of patients with asymmetric prognathism and measured neck mobility to assess for unrecognized torticollis (n=30). In part II, we compared patients treated for asymmetric prognathism with our novel approach of Le Fort I advancement with unilateral sagittal split mandibular osteotomy using only a final splint (Group 1) to the traditional 2 jaw method of a Le Fort I advancement with bilateral sagittal split mandibular osteotomy with an intermediate and final splint (Group 2) (n=60). Preoperative and postoperative exams and cephalometric measurements were compared to determine the stability of correction.

Results:  Part I: Of all patients treated for prognathism in our data bank 31% had asymmetric prognathism. All patients of thses patients had restrictive measured neck range of motion and cranial base tilt on upward gaze; based on these evaluations they were diagnosed with previously unrecognized torticollis. These pateints had posterior lateral crossbite on the side of the torticollis and deviation of the mandibular midline and chin point to the contralateral side. Three-dimensional CT scan assessment revealed an asymmetic cranial base in 85% of patients with slight anteriomedial displacement of the glenoid fossa ipsilateral to the torticollis. Part II: In Group 1 (novel unilateral split) Unilateral mandibular setback was performed ipsilateral to the side of the torticollis in all patients. Intraoperatively, all cuts and movements in both jaws were made and a final splint only was used to stabilize the new occlusal relationship while osteofixation was obtained. When Group 1 (novel unilateral split) was compared to Group 2 (traditional 2 jaw surgery) both were similar with regard to complications (infection 2-3%, bleeding 2%, hardware failure 1%, need for revisionary surgery 2%). Operative time was decreased in Gorup 1 by 15%. In Group I no patients complained of trismus, TMJ clicking or popping, or lateral deviation with incisal opening. All patients maintained a stable correction during a mean follow-up period of one year based upon physical exam findings and cephalometric analyses.

Conclusions:  Although a unilateral sagittal split solution may seem to violate some principles of orthognathic surgery, for these patients with asymmetric prognathism and unrecognized torticollis it provides successful correction. We were able to obtain stable results using this technique in the muscular torticollis patient while simultaneously decreasing morbidity and without compromising function.