Changes in temporomandibular joint and ramus after sagittal split ramus osteotomy in mandibular prognathism patients with and without asymmetry

The purpose of this study was to examine the changes in the temporomandibular joint (TMJ) and ramus after sagittal split ramus osteotomy (SSRO) with and without Le Fort I osteotomy. The subjects consisted of 87 Japanese patients diagnosed with mandibular prognathism with and without asymmetry. They were divided into 2 groups (42 symmetric patients and 45 asymmetric patients). The TMJ disc tissue was assessed by magnetic resonance imaging (MRI) and the TMJ space, condylar and ramus angle were assessed by computed tomography (CT) preoperatively and postoperatively. Medial joint space on the deviation side in the asymmetry group was significantly larger than that in the symmetry group (P = 0.0043), and coronal ramus angle on the non-deviation side in the asymmetry group was significantly larger than that in the symmetry group preoperatively (P = 0.0240). The horizontal condylar angle on the deviation side in the asymmetry group was significantly larger than that in the symmetry group (P = 0.0302), posterior joint space on the non-deviation side in the symmetry group was significantly larger than that in the asymmetry group postoperatively (P = 0.00391). The postoperative anterior joint space was significantly larger than the preoperative value on both sides in both groups (the deviation side in the symmetry group: P = 0.0016, the non-deviation side in the symmetry group: P < 0.0001, the deviation side in the asymmetry group: P = 0.0040, the non-deviation side in the asymmetry group: P = 0.0024). The preoperative disc position could was not changed in either group. These results suggest that significant expansion of anterior joint space could occur on the deviation side and non-deviation side in the asymmetry group as well as on both sides in the symmetry group, although disc position did not change in either group.