Morphological Features of the Mandibular Ramus Associated With Increased Blood Loss in Sagittal Split Ramus Osteotomy

Sagittal split-ramus osteotomy (SSRO) is the most common surgical procedure in orthognathic surgery¹. It has proved to be a safe technique with stable results, but various associated problems have not yet been overcome². However, few clinical studies have evaluated the surgical difficulty associated with SSRO. Previous reports have suggested a relationship between blood loss and surgical time in SSRO. Surgical difficulty may be correlated to the degree of surgical time and blood loss. The purpose of this study was to determine whether specific morphological features of the mandibular ramus can predict an increased blood loss in SSRO.

　This study evaluated 100 patients (200 sides) who underwent SSRO without maxillary surgery during the period from 2006 to 2013. No other concomitant surgical procedures were performed on the mandible, such as genioplasty, segmental osteotomy, or lingual cortical sectioning at the anterior border of the ramus. Physical data, such as height, weight, and body mass index, were collected. The morphological features of the mandibular ramus, obtained from computed tomography images (n = 200) before surgery, were analyzed. The surgical time, the time required for ablation of the medial mandibular ramus, the time required for the cutting of the mandible in performing a modified Obwegeser’s SSRO, and total blood loss were measured. Correlations among parameters related to the surgical time and blood loss were analyzed using Pearson’s coefficient covariant. All data were statistically analyzed using the JMP v8 software program (SAS Institute Inc., Cary, NC, USA). Differences were considered significant at P < 0.05.

　The median total surgical time and blood loss were 115 min (range, 80–200 min), and 80ml (range, 15-400ml), respectively. A correlation was observed between the total surgical time and blood loss (r = 0.496, P < 0.0001). With regard to the total surgical time, the time required for bone cutting was the most significantly correlated (r = 0.261, P < 0.001), followed by the time required for medial ablation (r = 0.210, P = 0.003). Blood loss was significantly correlated with the time required for bone cutting on the medial aspect of the mandibular ramus (r = 0.272, P < 0.0001), followed by the time required for medial ablation (r = 0.206, P < 0.003). Minimal width of the thinned ramus (median 5.3 mm, range 1.6–9.2 mm) was significantly related to the total surgical time (r = 0.149, P = 0.035) and blood loss (r = 0.179, P = 0.011). The distance from the incisor to the posterior border of the mandible (median 93.9 mm, range 82.0–107.0 mm) was significantly related to blood loss (r = 0.154, P = 0.03). We divided the axial aspects of the medial ramus into the following two types depending upon the difference between its maximal and minimal width: a moderately straight type (<2.8 mm), and a concave type (≥2.8 mm). There was a significant difference in blood loss (concave type, 102.7 ± .6.5 s; moderately straight type, 60.9 ± 6.1 s; P < 0.0001).

  A thinned ramus, and a greater distance between the mandibular incisors and the posterior border of the mandible may increase blood loss in patients undergoing classical SSRO. When planning or performing SSRO, the morphological features obtained from computed tomography images may help surgeons gain a better understanding of potential difficulties when the surgical site involves the medial aspect of the ascending ramus of the mandible.

1. Perez D, Ellis E 3rd: Sequencing bimaxillary surgery: Mandible first. J Oral Maxillofac Surg 69:2217-24, 2011

2. Lanigan DT, Hey J, West RA: Hemorrhage following mandibular osteotomies: a report of 21 cases. J Oral Maxillofac Surg 49:713-24, 1991