The Evaluation of Clinical and Anatomical Characteristics for the Development of Neurosensory Disturbance After Sagittal Split Ramus Osteotomy

During the last half century, sagittal split-ramus osteotomy (SSRO) method has gained widespread popularity and became the part of the most common surgical procedure in the field of orthognathic surgery. However, Previous studies¹ have reported various complications associated with SSRO. The SSRO may damage the nerve and cause neurosensory disturbance (NSD) of the lower lip, which is one of the most common and unpleasant postoperative complications². The present study aims to investigate the factors associated with the development of NSD on the basis of mandibular morphology on CT images and the surgical space located medial to the mandibular ramus.

  The study group comprised 100 patients (60 women and 40 men; age range, 16–46 years) who underwent consecutive series for performing SSRO (200 SSROs in total) between 2006 and 2013. All patients were candidates for mandibular osteotomy alone. Demographic data, such as age, sex, height, weight, and body mass index (BMI) were collected for all patients. And overall surgical duration in performing a modified Obwegeser’s SSRO and total blood loss were measured. The morphological features of the mandibular ramus, obtained from computed tomography images (n = 200) before surgery, were analyzed. Clinical sensory testing of the lower lip was performed at one week, six months, and one year after surgery using Semmes–Weinstein pressure esthesiometer filaments (Stoelting Co., USA). Correlations among parameters related to NSD development were analyzed by Student’s t-test and Fisher’s exact test. All data were statistically analyzed by the JMP software program v8 (SAS Institute Inc., Cary, NC, USA). Differences were considered statistically significant at P<0.05.

  NSD of lower lip at one week and six months after SSRO was observed in 34.2% (69/200) and 12.0% (24/200) of cases, respectively. There was a significant difference between patients with or without NSD one week after SSRO: operation time (appearance 123.1 vs. no appearance 111.2 min, P<0.001), lingual to the mandibular notch (14.0 vs. 15.2 mm, P=0.014), thickness of mandible (10.0 vs. 10.8 mm, P=0.008), width of the bone marrow space at the buccal side (1.7 vs. 2.1 mm, P<0.003). For post operative six months: lingual to the mandibular notch (13.4 vs. 15.0mm, P=0.026), thickness of mandible (9.2 vs. 10.7 mm, P<0.001), width of the bone marrow space at the buccal side (1.2 vs. 2.1 mm, P<0.001), surgical space on the medial side of medial side of the ramus (192.5 vs. 150.6 mm², P<0.001).

  These results suggested that Surgical procedure-related factors evaluated on pre-operative CT images, such as the distance between the mandibular canal and the buccal cortical plate and the working space on the medial side of the ramus, were identified and included as significant variables. Because NSD development after SSRO is the existence of a thinner mandibular ramus, careful use of a separator and a thin osteotome during SSRO is recommended. Limited periosteal degloving prevents excessive stretching of the inferior alveolar nerve during sagittal split ramus osteotomy, thus lowering neurosensory disturbance incidence. By knowing the preoperative risk factors for neurosensory disturbance, the operator makes it possible to consider the beneficial surgical techniques and the patient selection can be made of beneficial surgery. 

1. Chow LK, Singh B, Chiu WK, Samman N. Prevalence of postoperative complications after orthognathic surgery: a 15-year review. J Oral Maxillofac Surg 2007;65:984-92
2. Macintosh RB. Experience with the sagittal osteotomy of the mandibular ramus: a 13 year review. J Maxillofac Surg 1981;9:151-65