Several technical modifications based on the anatomical position of the neurovascular bundle and its bony mandibular canal have been developed, aiming to prevent injury to the intraalveolar nerve We hypothesized that the incidence of neurosensory disturbance (NSD) should be reduced using our bilateral sagittal split osteotomy (BSSO) technique, because direct intra-alveolar nerve injury can be avoided. The aim of this study was to introduce our modified BSSO technique and evaluate the subsequent incidence of postoperative neurosensory disturbance of the IAN.
The study was designed as a prospective cohort study. Consecutive patients scheduled for orthognathic surgery (OGS) conducted by the senior author at the Craniofacial Center, Department of Plastic and Reconstructive Surgery, Chang Gung Memorial Hospital between January and August 2013 were asked to participate. OGS procedures included mandibular BSSO with or without maxillary LeFort I osteotomy or genioplasty. Fifty-seven patients were enrolled. All patients received cone-beam computed tomography before surgery for intra-alveolar nerve (IAN) assessment and virtual surgery planning. During surgery, corticotomy and osteotomy lines are modified from the Obwegeser-Dal Pont method. After corticotomy completion, a Dautrey osteotome is driven into the mandible medulla via the anterior corticotomy, keeping constant contact to the inner side of the buccal ramus cortex for the first 10mm. The osteotome, located anterior and lateral to the IAN, is then twisted with moderate force, gradually separating the proximal and distal segment cortices along the anterior opening to facilitate visualization. Possible resistance to open the cortices indicates incomplete corticotomies located in the medial cortex, or the posterior and inferior aspects of both corticotomy lines. Before the complete split, the IAN is evaluated for any exposure through the anterior opening . If the IAN is exposed or attached to the outer cortex, it can gently be replaced into the distal segment. Under visualization through the anterior opening, a straight 4 or 6 mm osteotome is then inserted lateral to and passed beyond the IAN, and then hit to split the posterior ramus cortex along the inner surface of the proximal segment to reach the posterior border. A standardized record form was provided to all subjects before and after surgery. Gender, preoperative diagnosis and operative details were collected, including surgical plan, mandibular movement extent and concomitant surgical procedures i.e. LeFort I and genioplasty, problematic mandibular splitting and type of fixation. All BSSO procedures were divided into independent left and right sides. After successful splitting of the mandibular ramus, splitting results were categorized. A 5-point scale self-assessment questionnaire was used during the routine follow up visits to evaluate IAN neurosensory disturbance (NSD) after the BSSO procedure. The subjective neurosensory status evaluation was performed preoperatively, one week, 6 and 12 months postoperatively or until normal sensation returned.
Study Type
INTERVENTIONAL
Allocation
NA
Purpose
TREATMENT
Masking
NONE
Enrollment
57
surgical technique to split the mandibular ramus through three osteotomy lines on the medial-cranial, buccal-caudal and anterior surface to facilitate a split of the posterior border of the mandible without injury of the inferior alveolar nerve
Incidence of NSD 12 months postoperatively in relation to IAN exposure during surgery
For every patient, the incidence of IAN exposure is recorded. The incidence of NSD is evaluated 12 months after the procedure. The relation and statistical significance is documented with Chi-square-test.
Time frame: preoperative to at least 12 months after surgery or return of normal sensation; if no return of normal sensation, reevaluation after another 3 months with computer tomography and clinical exam
Longitudinal incidence of NSD in relation to gender, age, affected side, preexisting deformity, third molar extraction and genioplasty
Subanalysis of the patients in the above mentioned fashion. Clinical evaluation of neurosensory disturbance level of the intraalveolar nerve is carried out with self-assessment questionnaire grading as 1. Affected mandibular side is completely numb, 2. Affected mandibular side is numb with almost no sensation, 3. Affected mandibular side sensation is reduced with some intact sensation, 4. Affected mandibular side has almost normal sensation, 5. Completely normal sensation, no change at all. Subjective neurosensory status evaluation is performed preoperatively, one week, 6 and 12 months postoperatively or until normal sensation return, and absence of neurosensory disturbance was defined with the cutoff at 5 points in the scale. Neurosensory disturbance scores of 1 to 4 are considered abnormal. If the disturbance persists over 12 months, computed tomography and clinical evaluation are performed after additional 3 months.
Time frame: preoperative to at least 12 months after surgery or return of normal sensation; if no return of normal sensation, reevaluation after another 3 months with computer tomography and clinical exam
Longitudinal incidence of NSD in relation to split type during surgery
Subanalysis of the patients in the above mentioned fashion. After blinding and light touch on the areas with an 18 gauge needle, participants were asked to choose a score for each one of the tested sites from a scale of 1 to 5. The lowest score was rated as the neurosensory status score at the time of evaluation. Subjective neurosensory status evaluation is performed preoperatively, one week, 6 and 12 months postoperatively or until normal sensation return, and absence of neurosensory disturbance was defined with the cutoff at 5 points in the scale. Neurosensory disturbance scores of 1 to 4 are considered abnormal. If the disturbance persists over 12 months, computed tomography and clinical evaluation are performed after additional 3 months.
Time frame: preoperative to at least 12 months after surgery or return of normal sensation; if no return of normal sensation, reevaluation after another 3 months with computer tomography and clinical exam
Longitudinal incidence of NSD in relation to IAN exposure
Subanalysis of the patients in the above mentioned fashion. After blinding and light touch on the areas with an 18 gauge needle, participants were asked to choose a score for each one of the tested sites from a scale of 1 to 5. The lowest score was rated as the neurosensory status score at the time of evaluation. Subjective neurosensory status evaluation is performed preoperatively, one week, 6 and 12 months postoperatively or until normal sensation return, and absence of neurosensory disturbance was defined with the cutoff at 5 points in the scale. Neurosensory disturbance scores of 1 to 4 are considered abnormal. If the disturbance persists over 12 months, computed tomography and clinical evaluation are performed after additional 3 months.
Time frame: preoperative to at least 12 months after surgery or return of normal sensation; if no return of normal sensation, reevaluation after another 3 months with computer tomography and clinical exam
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