IAN Injury After BSSO in Oral Clefts

Orthognathic surgery is usually the final phase of treatment for patients with cleft lip and palate (CLP). More than 25% of patients with CLP develop a significant maxillary hypoplasia that requires surgical intervention, and maxillary osteotomy is, therefore, most commonly performed for these patients. If the sagittal discrepancy is too large or if there are associated mandibular deformities (e.g., asymmetries, canting of the mandibular occlusal plane), a simultaneous setback of the mandible is performed. The bilateral sagittal split osteotomy (BSSO) has become the preferred mandibular osteotomy in many centers for the treatment of mandibular deformities. Nevertheless, this treatment is known to give rise to various complications; sensory disturbance of the inferior alveolar nerve (IAN) is probably the most common one with the incidence ranging from 8% to 85%. Such sensory disturbances may affect patients' quality of life due to the difficulties in speech, eating and drinking. Patients may also complain about the inability to assess tactile stimuli such as putting on lipstick, shaving or kissing, which may lead to psychological and social issues.

IAN disturbance is believed to be caused by iatrogenic injury to the nerve including excessive nerve manipulation, nerve laceration, fixation of segments by incorrect placement of position screws, large mandibular movement and bad splits. Identification of risk factors for IAN disturbance after BSSO can help clinician to prevent it and raise the satisfaction level of patients. It is generally thought that the injury to IAN inside the mandibular ramus and body during surgery are highly correlated to variations in preoperative anatomy (ie, patient-related factors). Previous computed tomography (CT) studies have reported the anatomical variations including the thickness and length of ramus, the position and bone density of inferior alveolar nerve canal (IAC) and thickness of buccal and lingual cortical plate. However, few studies tried to identify surgery-related factors such as types of BSSO, extent of surgical correction, extent of split, concomitant genioplasty or third molar extraction. Furthermore, most of the studies were retrospective in design or had limited number of patients to conduct multivariate analysis to recognize the influences of patient- and surgery-related risk factors on IAN disturbance. Moreover, heterogeneity of the assessment timing and methods for IAN disturbance in previous studies prevented from overall assessment of the degree of IAN recovery. We therefore aim to (1) determine the incidence of IAN injury after BSSO, (2) identify the risk factors associated with such injuries, and (3) understand the consequences of such injuries including the degree of neurologic recovery by performing a prospective, longitudinal study.