Abstract
Bilateral sagittal split osteotomy (BSSO) aims to correct congenital or acquired mandibular abnormities. Temporary or permanent neurosensory disturbance is the most frequent complication of BSSO. To evaluate the influence of IAN handling during osteotomy, the authors undertook a prospective study in 290 patients who underwent BSSO. The occurrence and duration of paresthesia was evaluated 4 weeks, 3 months, 6 months, and 1 year after surgery. Paresthesia developed immediately after surgery in almost half of the patients. Most cases of paresthesia resolved within 1 year after surgery. A significantly higher prevalence of paresthesia was observed on the left side. The authors found a correlation between the type of IAN position between the left and right side. The type of split (and IAN exposure) did not have a significant effect on the occurrence or duration of neurosensory disturbance of the IAN. The authors did not find a correlation between the occurrence and duration of paresthesia and the direction of BSSO. Mandibular hypoplasia or mandibular progenia did not represent a predisposition for the development of paresthesia. In the development of IAN paresthesia, the type of IAN exposure and the split is less important than the side on which the split is carried out.
Bilateral sagittal split osteotomy (BSSO) aims to correct the position of the mandible. The first Hullihen orthognathic operation on mandible, anterior subapical osteotomy was published in 1984. Then, in 1954, Caldwell and Letterman described the intraoral vertical ramus osteotomy and in 1955 BSSO was introduced into routine orthognathic surgery by Obwegeser and Trauner. Until then, the most important modifications of BSSO were by Dal Pont in 1961, Hunsuck in 1968, Gallo in 1976 and E pker in 1977 (for a review, see ).
In contrast to the many modifications of BSSO, its use encompasses complications, mainly temporary or permanent damage to the inferior alveolar nerve (IAN). Despite intensive preclinical and clinical research, the particular cause of many such cases is unknown. Two main causes have been cited in the literature: handling the IAN during osteotomy and medial retraction of the extraosseous portion of the IAN at the time of medial horizontal ramus osteotomy . The latter cause is indirectly supported by studies describing a contemporaneous disturbance of the lingual nerve . The exact pathophysiological mechanism leading to disturbance to the IAN remains to be elucidated.
The authors examined if preparative positioning of the IAN at the osteotomy site, as well as the direction of movement of osseous fragments, have a role in paresthesia after BSSO.
Patients and methods
The study was designed as a prospective investigation. The study protocol was approved by the Ethics Committee of Charles University (Prague, Czech Republic). All subjects enrolled in the study provided written informed consent. Between 2006 and 2008, the authors operated on 535 patients, 399 of whom had a BSSO, of these, 290 patients were included in the study. The inclusion criteria were: ability of the patients to undergo detailed preoperative and postoperative examination; normal function of the IAN preoperatively; ability to obtain documentation during the entire follow-up period; absence of concomitant disease (particularly cardiovascular or neurological disease); carrying out a BSSO; and absence of genioplasty. Patients who did not meet these criteria were excluded. Most were excluded owing to failure in their follow-up. Of the 290 patients studied, 190 were women and 100 were men. In the preoperative examination, all patients had normal sensation in the lip and chin area. All had standard preoperative orthodontic decompensation with fixed appliances.
BSSOs were performed by one surgeon (R.F.) in all cases. In all patients, opening of medial tissue, osteotomizing, and splitting of the mandible were first done on the right side, then on the left. The osteosynthetic phase was first carried out on the right side, and subsequently on the left.
All surgery was carried out under general anaesthesia. The surgical procedure was the standard Hunsuck–Epker modification of BSSO from a clearly intraoral approach with minimal dissection of soft tissue. The authors used standard Obwegeser hooks for visualization of the lingula on the medial ramus and the lateral lower border of the mandible. Osteotomy was carried out with burrs and finished with Obwegeser chisels and, in some cases, with Smith’s spreader. For internal rigid fixation, only miniplates with monocortical screws were used: lag screws were never used. After surgery, patients were put on soft elastic intermaxillary fixation for 6 weeks with early mobilization after 3 weeks.
The IAN was spared during the entire procedure. During medial opening, the authors carried out as minimal retraction of soft tissue as possible, and repeatedly confirmed the position of the IAN. During sawing, the depth of the osteotomy was controlled (mainly during the anterior cut of the inferior margin of the mandible). During splitting, the insertion of Obwegeser chisels was minimized. After splitting, the nerve position was controlled. Sharp bony interferences in the osteotomy area were meticulously removed if necessary. If the nerve was fixed to a joint-bearing fragment, special care was taken to detach the nerve precisely without damaging it. If the IAN was cut partially or totally, a microsuture of its perineurial sheath end-to-end with Ethilon 10/0 was carried out immediately. The necessity of using tension-free sutures required more intensive detachment of the nerve from the proximal part of the mandibular canal. To minimize the possibility of nerve damage during the osteosynthesis, only monocortical miniplates were used for fixation. Suturing was done with resorbable material, drains were not used.
Postoperatively, patients spent at least 12 h in the intensive care unit (ICU). The mean postoperative duration of hospital stay was 4.5 days. Patients remained on antibiotics for 5 days postoperatively. Early mobilization was started on the third week after surgery. This was followed by full-mouth-opening rehabilitation by a physiotherapist starting at the sixth week after surgery.
Monitoring the position and function of the IAN
Before surgery, detailed examination of the patients was undertaken. This involved taking a medical history, physical examination, orthodontic examination, and pre-treatment and orthognathic surgical planning, as previously described . Particular care was taken to confirm or exclude neurological disturbances (particularly around the trigeminal nerve) during the extended physical examination, focusing on neurological disturbances.
On the basis of experience with >1000 cases treated with orthognathic surgery, the authors have found that the course of the IAN is very variable, but its position during osteotomy could be divided into five main situations. The authors introduced their own five-point classification based on the classification of T eerijoki – Oksa et al. . In contrast to this study, the authors considered whether the nerve was attached to the lateral fragment, which they evaluated as very important for the subsequent necessity of manipulating the nerve. After the mandibular split, the position of the IAN was evaluated in all cases on the right and left side separately and the corresponding category noted ( Table 1 ). On the basis of the position of the IAN, the surgical technique was modified to prevent nerve damage.
| Type | Position and course of the nerve | Procedure |
|---|---|---|
| I. | The nerve is covered by cortical bone during the whole course in the mandibular canal | None |
| II. | The nerve remains in the mandibular canal on the medial fragment, but at least one side of the canal is missing | Targeted preservation of the nerve during manipulation and fixation of the fragments |
| III. | The nerve is in the middle of the fragments in an osteotomy line | Procedure in II together with cancellous bone removal on lateral fragment |
| IV. | The nerve is attached to lateral cortical bone | Procedure in III together with suitable detachment of the nerve |
| V. | The nerve is partially or completely cut | Procedure in IV together with end-to-end microanastomosis |
After surgery, all patients were instructed to pass four recall controls at certain times after surgery: 4 weeks (T1); 3 months (T2); 6 months (T3); and 1 year (T4). The evaluation of neurosensory disturbances was evaluated subjectively by the patient using an anonymous questionnaire, filled in by the patient at each time period. During evaluation of the results, the authors included only data on the presence or absence of neurosensory disturbance, not its severity.
Statistical analyses
For each patient, age, sex, type of surgery, type of split on the right and left side, presence of IAN disturbance on the right and left side, and the duration of IAN disturbance on the right and left side were noted. Data on age are mean ± SEM. Statistical analyses involved the Wilcoxon signed ranks test, the Mann–Whitney test, the Kruskal–Wallis test and Pearson’s χ 2 test ( p < 0.05).
Results
The mean age of the patients was 27.04 ± 0.44 years (range 17–57 years). Isolated mandibular advancement was performed in 177 patients; isolated set-back was carried out in 84 patients. 29 patients underwent a BSSO with a change in occlusal plane rotation; of these, 13 had clockwise rotation and 16 had counter-clockwise rotation. All patients underwent a BSSO without severe intraoperative or postoperative complications.
Neurosensory disturbance of the IAN
Of 290 patients, almost half observed neurosensory disturbance in the area of the IAN within the fourth postoperative week, but only 3% suffered from a neurosensory disturbance after 1 year ( Table 2 ; Fig. 1 ). Together, >28% of IANs were affected ( Table 3 ). On the left side, the authors observed a significantly higher occurrence of paresthesia compared with the right side ( p = 0.012) ( Table 3 ). They did not observe a statistically significant difference in the duration of paresthesia between the right and left site ( Fig. 1 ). Correlation of the development of paresthesia between the right and left side was not observed. A relationship between the occurrence of paresthesia or duration of paresthesia, both between women and men was not observed. An age-dependent relationship of the occurrence and duration of paresthesia was not found. There was no significant difference in the duration of IAN disturbance amongst younger patients (17–23 years) and older patients (24–57 years).
| Time after surgery | Number of patients with paresthesia N = 290 | |
|---|---|---|
| T1 | 4 weeks | 140 (48.3%) |
| T2 | 3 months | 59 (20.3%) |
| T3 | 6 months | 29 (10.0%) |
| T4 | 1 year | 9 (3.1%) |
| Number of patients | Number of affected nerves | |
|---|---|---|
| Paresthesia (left side) | 70 (24.1%) | 70 (12.1%) |
| Paresthesia (right side) | 45 (15.5%)* | 45 (7.8%)* |
| Paresthesia (bilateral) | 25 (8.6%) | 50 (8.6%) |
| Paresthesia | 140 (48.3%) | 165 (28.4%) |
| Total | 290 (100.0%) | 580 (100.0%) |
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