Anatomic Study for the Horizontal Cut of the Sagittal Split Ramus Osteotomy

PurposeThe purpose of this study was to determine the posterior extension of trabecular bone and the height at which both the lateral and medial cortical bone layers of the mandibular ramus merge, using a reference point on the anterior margin of the mandibular ramus.Materials and MethodsA total of 80 adult human mandibles were studied. Starting at reference point X, we marked a line running from the anterior margin to the posterior margin of the mandibular ramus on the medial aspect of the study samples. On 2 vertical sections of the right ramus, the level at which both the medial and lateral cortical bone layers merged was determined—H1 and H2, respectively. On the horizontal cross section of the left mandible at point X, the posterior extension of trabecular bone was determined.ResultsThe median values of H1 and H2 were 10.45 mm and 4.52 mm, respectively. The median value of H2 was inversely proportional to the width of the ramus. The mean extension of trabecular bone posterior to point Z (where the upper margin of the lingula merges into the continuous medial aspect of the ramus) was 17.17 mm, bearing no correlation with the ramus width.ConclusionPoint X is a safe and easy-to-find anatomic reference to establish the level of a sagittal split ramus osteotomy (SSRO) horizontal cut. The wider the mandibular ramus, the closer to the mandibular foramen the SSRO horizontal cut should be performed. An SSRO horizontal cut should not be performed farther than 4 mm above line X. A safe posterior limit for the SSRO horizontal cut could not be determined.