A randomized clinical trial was performed to evaluate differences in postoperative neurosensory disturbance (NSD) between two methods of mandibular advancement surgery. A total of 66 non-syndromal class II patients with mandibular hypoplasia were randomized for either distraction osteogenesis (DO) or bilateral sagittal split osteotomy (BSSO). Twenty-nine patients in the BSSO group and 34 patients in the DO group were available for evaluation. Objective assessment was performed by Semmes–Weinstein (SW) monofilament testing preoperatively and at least 1 year after surgery. Six of the 34 patients (17.6%) in the DO group experienced objective NSD, compared to 5/29 patients (17.2%) in the BSSO group. In the evaluation of nerve function by individual nerves, 8/68 nerves (11.8%) revealed objective NSD in the DO group, compared to 7/58 nerves (12.1%) in the BSSO group. A subjective NSD was reported in 11/34 patients (32.4%) in the DO group, compared to 9/29 patients (31.0%) in the BSSO group. In the evaluation of nerve function by individual nerves, a subjective NSD was reported for 13/68 nerves (19.1%) in the DO group, compared to 13/58 nerves (22.4%) in the BSSO group. None of the differences was significant. No differences in neurosensory disturbance could be found between the two study groups. Objective WS monofilament testing appeared to underestimate NSD compared to subjective patient report.
In Western Europe, hypoplasia of the mandible with an Angle class II occlusion, convex profile, and a deficient chin is the most common growth disorder of the facial skeleton. In 1957, Trauner and Obwegeser described the bilateral sagittal split osteotomy (BSSO), and since then it has been feasible to advance the mandible to a normal profile and a class I occlusion with this relatively simple procedure. However, despite several modifications, this procedure still has some drawbacks. The main concerns are numbness of the lip and chin region and relapse. Skeletal stability has much improved with the use of stable internal fixation with miniplates or screws in place of wire fixation. Neurosensory disturbances (NSD) of the inferior alveolar nerve (IAN) are still the most common complication in mandibular surgery, with a rate ranging from 0% to 87% at 1 year after surgery, depending on the timing and type of assessment of the nerve impairment.
Ilizarov introduced distraction osteogenesis (DO) for the long bones in the 1950s. Decades later, this technique became suitable for application to the bones of the facial skeleton, and finally in 1992 McCarthy et al. described the first intraoral distractor. With these intraoral, transbuccal, distractors, the facial skeleton could be advanced leaving scars on the face. Some early users of this new method reported less neurosensory disturbance and a more stable result compared to the BSSO procedure. However, these findings could not be verified in other studies. In a patient-controlled study to compare the two procedures, there were no differences regarding NSD, or any differences in short-term or long-term skeletal stability.
The purpose of this investigation was to compare BSSO and DO procedures for advancement of the mandible in a randomized clinical trial. The main focus was on NSD and skeletal stability. In this first part, the results for NSD are reported.
Materials and methods
Between March 2008 and July 2011, 66 patients were included in this prospective study ( Fig. 1 ). All patients were treated in the same clinic in the Netherlands. Within this department there are residents undergoing training in oral and maxillofacial surgery. All surgeries were performed by one staff surgeon (JdeL, FB, or EB) together with one of the residents.
All patients had a hypoplastic mandible with an Angle class II malocclusion and needed advancement of the mandible to obtain a class I relationship. Exclusion criteria were previous mandibular surgery and age >35 years. No other mandibular procedures were done in any patient. Patients were informed about the purpose of the study and all patients and/or their parents provided informed consent to participate. Patients were assigned randomly to the BSSO or the distraction procedure. Randomization was done using a randomized generated list ( www.randomization.com ) with a fixed block size of 20 patients. One person, not involved in the study, prepared closed envelopes numbered 1–80 with the assigned therapy enclosed. After providing informed consent, the patient was present when the envelope containing the assigned surgical procedure was opened. This study was approved by the hospital medical ethics committee.
Patients were evaluated in a standard manner before and after surgery. All assessments were done by a single investigator who was trained in neurosensory testing (EB). Assessment of the objective NSD was done preoperatively, at 4 months postoperatively, and at least 1 year after the surgery. Patients completed a questionnaire for subjective evaluation of NSD at 1 year after surgery.
Sensory impairment was assessed by the mechanoreceptive response (Aα nerve fibres) to a cutaneous stimulus in the region innervated by the IAN. Objective neurosensory disorders were tested by determination of the light touch detection threshold with a Semmes–Weinstein (SW) monofilament (North Coast Medical, Inc., San Jose, CA, USA); monofilaments ranged in size from 1.65 to 4.08.
All tests were performed bilaterally at the midway of the corner of the mouth and the midline. The skin of the lip on the mucocutaneous junction and the chin midway down the labiomental fold was tested. Before the actual light touch detection threshold was recorded, a series of stimuli with ascending and descending SW monofilaments was performed in order to establish the range in which the light touch detection threshold could be found. The light touch detection threshold test was started with the smallest SW monofilament recognized in these ascending/descending series.
Patients were asked to identify the SW monofilament stimulus at two intervals with eyes closed. Only at one interval was the stimulus applied; this was done by placing the SW monofilament perpendicular to the skin until it bent. The stimulus was applied randomly at either the first or second interval. When the patient identified over 80% of the 10 applied stimuli correctly, the procedure was repeated with a smaller SW monofilament. When the patient failed to identify over 80% of the correct stimuli, the same procedure was performed with a larger-sized SW monofilament. The baseline measurement of the smallest SW filament that could be detected was taken preoperatively. Postoperative measurements were taken at 4 months and at ≥12 months (mean 22, range 12–48 months). Baseline measurements for most patients were SW monofilament 1.65 or 2.36. If the patient failed to identify the baseline SW monofilament after 12 months, they were recorded as having an NSD. Results were recorded at the nerve level as well as at the patient level.
For the assessment of subjective NSD, patients were asked to complete a questionnaire 1 year after surgery. A visual analogue scale (VAS) was used, comprising a horizontal line of 100 mm, ranging from no complaints on the left-hand side to severe complaints on the right. The VAS score was measured in millimetres and divided into five categories.
Advancement was measured at the incisal edge of the lower incisors on consecutive lateral cephalograms.
The surgical procedure
Surgery was performed under general anaesthesia in both groups. Preoperatively, 2 g cefazolin and 0.5 mg/kg dexamethasone were given intravenously. Another dosage of 10 mg dexamethasone was given 8 and 16 h postoperatively.
The bilateral sagittal split advancement osteotomy was carried out according to the method of Obwegeser/Dal Pont modified by Hunsuck. After infiltration of the mucosa with articaine (Ultracaine DS Forte), an intraoral vestibular incision was made and a mucoperiosteal flap raised. The inferior alveolar nerve was identified at the lingula. The medial horizontal osteotomy cut was made with a Lindemann bur, just above the lingula and extended along the external oblique line and finally through the lower border. The osteotomy of the mandible was then performed with a Smith ramus separator and sagittal separator left/right (Biomet Microfixation, Jacksonville, FL, USA) without the use of chisels. After advancement, the planned occlusion was established using a thin inter-occlusal acrylic splint; the proximal segments were placed into the correct position in the fossa and titanium miniplates were used for fixation (2.0-mm plates; Synthes GmbH, Solothurn, Switzerland). The miniplates were fixed with at least two monocortical 5- or 7-mm screws on each side of the osteotomy. After 1 week, guiding elastics were placed for 4 to 6 weeks, if required.
The mucosa was infiltrated with articaine (Ultracaine DS forte). A buccal vertical cut was made with a Lindemann bur just behind the second molar, followed by removal of the third molar if still in situ. The mono-directional distractor device (Zurich Distractor; KLS Martin GmbH & Co., Tuttlingen, Germany) was then adapted and placed parallel to the occlusal plane. After removal of the distractor, the osteotomy was completed and the distractor then immediately refitted in the marked position and fixed with three monocortical screws on each side. Before wound closure, the distractor was activated to confirm proper functioning, and finally the distractor was returned to its original position.
After a latency period of 5–7 days, the distractor devices were activated twice a day, resulting in 1.0 mm lengthening of the distractor device each day. Distraction was continued until a class I occlusion was attained. During this period, guiding elastics were placed. When the desired position had been achieved, a consolidation period of 8 to 10 weeks was completed before the devices were removed under general anaesthesia.
Postoperative guiding elastics were placed and patients were told to refrain from chewing and to maintain a soft diet for 6 weeks in the case of BSSO, or 8–10 weeks in the case of DO.
The data were analyzed using SPSS version 18.0 software (SPSS Inc., Chicago, IL, USA). Continuous data were analyzed with the Student t -test and dichotomous data with the Pearson χ 2 test.
A total of 66 patients were included in the study. After randomization they were assigned to either the BSSO group (32 patients) or the DO group (34 patients). Two patients in the BSSO group were lost to follow-up, and for one patient assigned to the BSSO group, the surgical procedure was changed from a bilateral procedure to a unilateral sagittal split osteotomy instead. Therefore 29 patients/58 IANs in the BSSO group and 34 patients/68 IANs in the DO group were available for evaluation ( Table 1 ).
|Number of patients included||32||34||66|
|Lost to follow-up/unilateral SSO a||3||0||3|
|Number of patients evaluated||29||34||63|
|Number of nerves evaluated||58||68||126|
|Mean age (years) b||18.6||21.3||20.1|
|Age range (years) b||14.3–26.7||14.7–34.8|
|Mean advancement (mm)||7.0||7.3||7.2|
|Range of advancement (mm)||4–12||5–12|
Although patients were assigned randomly to either group, there was a significant difference in age between the groups. Patients in the BSSO group (age range 14.3–26.7 years) appeared to be 2.7 years younger on average than those in the DO group (age range 14.7–34.8 years).
There was no difference in gender distribution between the two groups: the BSSO group comprised 12 males and 17 females, and the DO group comprised 16 males and 18 females ( P = 0.651).
The mean advancement in the BSSO group was 7.0 mm (range 4–12 mm) and in the DO group was 7.3 mm (range 5–12 mm) (difference not significant (NS), P = 0.506).
Objective neurosensory disorders
Patients were evaluated for NSD at 4 months. Nine of the 63 patients (14.3%) were missing. In total, 54 patients/108 IANs were available for assessment by neurosensory tests at 4 months. Objective NSD was found in 17 patients/24 nerves. In the BSSO group there were six patients (26.1%)/nine nerves (19.6%) and in the DO group there were 11 patients (35.5%)/15 nerves (24.2%) with impairment of the IAN (NS, P = 0.462 (patient level), and NS, P = 0.567 (nerve level)) ( Tables 2 and 3 ).
After at least 1 year (mean 22, range 12–48 months), objective NSD tested with SW monofilaments was found in six patients in the DO group (17.6%) and in five patients in the BSSO group (17.2%), with a NSD rate of 17.5% for the whole group ( Table 4 ). There was no significant difference between the two procedures (NS, P = 0.966).
At the nerve level (126 nerves), objective NSD was found in 15 nerves (11.9%) ( Table 5 ). Eight nerves (11.8%) in the DO group and seven nerves (12.1%) in the BSSO group showed objective NSD. There was no significant difference between the two groups (NS, P = 0.958). None of the patients had total numbness/anaesthesia of the lip or chin region.
With regard to the localization of the objective NSD at the nerve level, numbness was located in the lip region for eight sides and the chin region for six sides. For one side, both the lip and chin revealed a change in the light touch detection threshold.
Subjective neurosensory disorders
In the questionnaires completed at 1 year postoperatively, subjective NSD was reported by 11 patients (32.4%) in the DO group and nine patients (31.0%) in the BSSO group ( Table 6 ). This difference was not statistically significant (NS, P = 0.911). A total of 20 patients (31.7%) encountered persistent subjective NSD.
Measured at the nerve level, subjective NSD was found in 26 nerves (20.6%) out of the 126 nerves tested ( Table 7 ). In the DO group, 13 nerves (19.1%) showed subjective NSD, and in the BSSO group, 13 nerves (22.4%) showed subjective NSD (NS, P = 0.649). In total, 14 patients reported unilateral impairment and six patients reported bilateral impairment of the IAN. None of the patients experienced total numbness/anaesthesia of the lip or chin.
Objective sensory testing with the SW monofilament showed poor sensitivity of only 30.8% and positive predictive value of 53.3%, but acceptable specificity of 93% and negative predictive value of 83.8%. This means that SW monofilament testing was only able to detect eight of the 26 nerves with a subjective NSD (18 false-negative test results) ( Table 8 ).
|Objective NSD||Subjective NSD||Total|
The severity of the complaints related to IAN function was evaluated with a VAS ( Table 9 ). The 43 patients who did not have any subjective NSD after 1 year reported the severity of their complaints as follows: no complaints for 12 patients, mild for 23 patients, mild to moderate for four patients, and moderate for four patients. There was no difference between patients in the DO and BSSO groups (NS, P = 0.677).
|Subjective NSD||Severity of complaints||Total|
|None||Mild||Mild to moderate||Moderate||Moderate to severe||Severe|
The 20 patients who reported subjective NSD after 1 year rated the severity of their complaints as follows: mild for 14 patients, mild to moderate for three patients, moderate for one patient, and moderate to severe for one patient. Again there was no difference between the DO and BSSO group (NS, P = 0.485).
General risk factors for neurosensory disorders after mandibular surgery
The mean age of the patients reporting subjective NSD was 20.90 years (20 patients/26 nerves), compared to 19.69 years in patients reporting normal IAN function (43 patients) (NS, P = 0.433) ( Table 10 ).
|Subjective NSD||Number of patients||Age b|
The mean age of patients with objective NSD was 21.40 years (11 patients/15 nerves), compared to 19.79 years for patients with normal NSD tests (52 patients) (NS, P = 0.369) ( Table 11 ).
|Objective NSD||Number of patients||Age b|
In total, 20 patients reported subjective NSD: 14 nerves were impaired in 10 males and 12 nerves were impaired in 10 females (NS, P = 0.545) ( Table 12 ).
Objective NSD was found in 10 males/14 nerves and in only one female/one nerve. This difference was highly significant ( P = 0.001) ( Table 13 ).
The mean advancement in patients reporting subjective NSD was 6.95 mm (20 patients), compared to 7.30 mm (43 patients) in those reporting no subjective NSD (NS, P = 0.449) ( Table 14 ). The mean advancement in patients with objective NSD was 7.27 mm (11 patients), compared to 7.17 mm ( n = 52) in those with normal NSD tests (NS, P = 0.862) ( Table 15 ).