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CRANIOMAXILLOFACIAL DEFORMITIES/COSMETIC SURGERY
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Does Intraoral Miniplate Fixation Have a Good Postoperative Stability After Sagittal Splitting Ramus Osteotomy? Comparison With Intraoral Bicortical Screw Fixation Yuki Matsushita, DDS, PhD,* Koichi Nakakuki, DDS, PhD,y Machiko Kosugi, DDS,z Kazuto Kurohara, DDS, PhD,x and Kiyoshi Harada, DDS, PhDk Purpose:
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Bicortical screw fixation systems and miniplate with monocortical screw fixation systems have been reported mainly in bilateral sagittal split ramus osteotomy (BSSO). This study compared postoperative stability between these 2 fixation systems by an intraoral approach.
Materials and Methods:
This was a retrospective cohort study. The study sample was composed of patients treated by BSSO at the authors’ institute from January 2006 through December 2012. All cases had facial symmetry and were performed by setback surgery. The predictor variable was treatment group (intraoral screw fixation [SG] vs intraoral miniplate fixation [MG]), and the primary outcome variable was stability defined as the change in the position of point B. Other outcome variables were stability defined as the change in the position of the menton, blood loss, incidence of postoperative temporomandibular joint disorder, and nerve injury. Descriptive and bivariate statistics were computed and the P value was set at .05.
Results:
Seventy-five patients (35 men and 40 women; mean age, 25.8 yr) were divided into 2 groups (39 SG cases and 36 MG cases). Postoperative changes at point B and the menton in the 2 fixation groups were not statistically different. Lingual nerve injury occurred only in SG cases. Moreover, total blood loss was greater in SG cases.
Conclusion:
An intraoral miniplate with monocortical screw fixation system is recommended over intraoral bicortical screw fixation for bone segments in setback BSSO in patients without facial asymmetry. Ó 2015 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg -:1-9, 2015
Bilateral sagittal split ramus osteotomy (BSSO) is a popular surgical procedure for patients with mandibular prognathism. After rigid internal fixation (RIF) systems using bicortical screws or miniplates with monocortical screws were first described in the 1970s,1,2 these
2 fixation systems have been compared for postoperative stability.3 In general, almost all bicortical screw fixation systems need extraoral buccal skin incisions for trocar insertion.4,5 Despite the small wound, some patients worry about esthetic problems
*Research Fellow, Department of Maxillofacial Surgery, Graduate
kProfessor, Department of Maxillofacial Surgery, Graduate School
School of Medical and Dental Sciences, Tokyo Medical and Dental
of Medical and Dental Sciences, Tokyo Medical and Dental
University, Tokyo; Assistant Professor, Department of Clinical Oral
University, Tokyo, Japan.
Oncology, Nagasaki University Graduate School of Biomedical
Address correspondence and reprint requests to Dr Harada:
Sciences, Nagasaki, Japan.
Department of Maxillofacial Surgery, Graduate School of Medical
yAssistant Professor, Department of Maxillofacial Surgery,
and Dental Sciences, Tokyo Medical and Dental University, Tokyo,
Graduate School of Medical and Dental Sciences, Tokyo Medical
113-8549, Japan; e-mail: [email protected]
and Dental University, Tokyo, Japan. zResearch Fellow, Department of Maxillofacial Surgery, Graduate
Received March 12 2015 Accepted June 2 2015
School of Medical and Dental Sciences, Tokyo Medical and Dental
Ó 2015 American Association of Oral and Maxillofacial Surgeons
University, Tokyo, Japan.
0278-2391/15/00816-2
xAssistant Professor, Department of Maxillofacial Surgery,
http://dx.doi.org/10.1016/j.joms.2015.06.148
Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
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FIGURE 1. Two systems for intraoral mandibular fixation. A, Intraoral bicortical screw fixation system. B, Intraoral miniplate with monocortical Q10 screw fixation system. (Fig 1 continued on next page.) Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
because scars sometimes remain. The incidence of external scars after trocar insertion have been reported to be 18%.4 From the early 1990s, intraoral bicortical screw fixation systems have not been reported to cause facial skin scarring or paralysis of the mandibular branch of the facial nerve.6 During the late 1990s, bicortical screw fixation systems by an intraoral approach were adopted at the authors’ institute.7 The authors previously presented the results of desirable stability characteristics of an intraoral bicortical screw fixation system.7 Recently, however, miniplates with monocortical screw fixation systems have been reported to be more stable compared with those used in the past.8-12 One group reported that an intraoral miniplate fixation system was as stable as an extraoral bicortical screw fixation system.13 Moreover, another group indicated that the application of thicker, wider miniplates with monocortical screws had equal durability compared with standard miniplates and bicortical screws.14 However, there are few reports that mention a comparison between intraoral screw and intraoral miniplate fixation systems.15 The purpose of this study was to compare postoperative stability between an intraoral bicortical screw fixation system and an intraoral miniplate with monocortical screw fixation system. The authors hypothe-
sized that the availability of the2 systems were equal and it was desirable to choose the system depending on the surgeon’s preference. The specific aims of the study were to measure and compare changes in the positions of point B and the menton (Me) over time.
Materials and Methods STUDY DESIGN AND SAMPLE
To address the research purpose, the authors designed and implemented a retrospective study. The study population was composed of all patients presenting for evaluation and management of BSSO at the Department of Maxillofacial Surgery, Tokyo Medical and Dental University Hospital (Tokyo, Japan) from January 2006 through December 2012. This study was approved by the Tokyo Medical and Dental University Hospital institutional review board and all participants accepted an informed consent agreement. To be included in the study sample, patients had to fulfill the following inclusion criteria: undergo followup for more than 6 months after surgery, a difference in setback distances between the right and left sides less than 5 mm, surgery performed by 4 surgeons who had acquired familiarity with orthognathic surgery and with more than 10 years of clinical
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FIGURE 1 (cont’d). C, Postoperative radiograph of an intraoral bicortical screw fixation system. (Fig 1 continued on next page.) Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
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experience, and using intraoral bicortical screw fixation or an intraoral miniplate with monocortical screw fixation to fix the 2 fragments. Patients were excluded as study subjects if they had a combination of these 2 fixation systems, absorbable fixation systems, or an extraoral approach using a trocar, had cleft lip or palate, simultaneously underwent genioplasty, or underwent advanced surgery. SURGICAL PROCEDURE
BSSO was performed using methods described previously.16,17 In all cases, condylar positioning devices (CPDs) were applied to reposition the proximal segment when the proximal and distal segments were re-fixed. A miniplate was placed at the anterior
border of the mandibular ramus, the arch bar was fitted to the buccal tube of the upper first molar, and then the arch bar was fixed. Thus, the distance between the mandibular ramus and maxilla was maintained. Using CPDs, bilateral condyles were maintained at their presurgical positions. The incongruity between the proximal and distal segments was eliminated. Even if there were discontinuities between the segments, the segments were fixed to maintain the spacing. The present fixation system by an intraoral approach is shown in Figure 1. Before the 2 segments were fixed, intermaxillary fixation (IMF) was performed. A contra-angle handpiece was inserted intraorally under the periosteum in the 2 groups of patients. In the group that underwent intraoral bicortical screw fixation (SG), 3 bicortical screws were fixed
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FIGURE 1 (cont’d). D, Postoperative radiograph of an intraoral miniplate with monocortical screw fixation system. Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
near the anterior border of the mandibular ramus (Fig 1A, C); in the group that underwent intraoral miniplate with monocortical screw fixation (MG), a 4-hole miniplate was fixed at approximately the same position (Fig 1B, D). After the screws or miniplates were placed, IMF was released. Then, the occlusion was checked and the wound was sutured. VARIABLES
In this study, treatment group (SG vs MG) was set as the primary predictor variable. Stability defined as the change in the position of point B over time was set as the primary outcome variable. Stability defined as the change in the position of the Me over time, blood loss during surgery, incidence of postoperative temporomandibular joint disorder, inferior alveolar nerve
injury, and lingual nerve injury were the secondary outcome variables. Other study variables included age, gender, amount of setback, and the difference in displacement on the right and left sides. DATA COLLECTION METHODS
Lateral cephalograms were analyzed at 3 different time points (before surgery, 5 days after surgery, and >6 months after surgery). The standard x axis was constructed by drawing a line through the sella turcica 6 downward from the line connecting the sella to the nasion.18 The y axis was drawn as a straight line crossing the x axis and passing through the sella turcica. The positions of point B and the Me were measured horizontally and vertically at each time point (Fig 2).
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FIGURE 2. Standard x and y axes and measurement points (point B and the menton) are shown. FH, Frankfurt horizontal; SN, sella and nasion. Q11 Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
DATA ANALYSIS
To compare the pre- and postoperative positions of point B and the Me, the Wilcoxon signed rank test was performed. Measurement values were defined as the mean measured 3 times by 2 measurers.
Results No complication occurred during the perioperative or postoperative period. A total of 131 patients who had undergone BSSO during the study period were reviewed retrospectively. Of these 131 patients, 75 patients who fulfilled the criteria were examined (35 men, 40 women; age range, 18 to 35 yr; average, 25.8 yr). They were divided into 2 different groups according to the RIF system (SG group, 39 patients; MG group, 36 patients). Details of patients in the SG and MG groups are listed in Table 1. In the SG group, the mean amount of setback was 7.4 mm at the right first molar and 7.1 mm at the left first molar, whereas in the MG group, the mean amount of setback was 7.4 mm on the right side and 7.4 mm on the left side. Correlations between changes in the positions of point B and the study variables are presented in Table 2. Changes in the positions of point B and the Me at each time point were measured on lateral cephalograms and are presented in Tables 3 and 4. To examine stability from immediately after surgery to more than 6 months
after surgery, the amounts of movement at point B and the Me between the 2 fixation groups were compared. However, there was no statistical difference between the 2 groups (Fig 3). In the other examinations, 5 patients in the SG group and 8 patients in the MG group reported postoperative temporomandibular disorder symptoms (P = .23). Inferior alveolar nerve injury occurred in the 2 groups and symptoms remained in some of these cases during the follow-up period (SG group, 9 cases; MG group, 7 cases). However, there was no statistical difference between the 2 groups. Lingual nerve injury occurred only in the SG
Table 1. DETAILS OF THE SG AND MG GROUPS
Sample size Men Age (yr) R setback (mm) L setback (mm) Difference (mm)
SG
MG
P Value
39 (52.0%) 24 (61.5%) 25.1 5.9 7.4 2.5 7.1 2.3 2.0 1.8
36 (48.0%) 11 (31.4%) 26.6 9.4 7.4 2.4 7.4 2.5 2.2 1.6
.01 .44 .92 .64 .49
Abbreviations: L, left; MG, intraoral miniplate with monocortical screw fixation; R, right; SG, intraoral bicortical screw fixation. Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
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Table 2. CORRELATION BETWEEN CHANGES IN THE POSITION OF POINT B AND STUDY VARIABLES
Point B on x Axis From T1 to T2 Sample size Gender Men Women Age (yr) #22 (n = 39) $23 (n = 36)
P Value
Point B on y Axis From T1 to T2
75
P Value
75
0.08 0.48 0.23 0.47
.18
0.09 0.93 0.00 0.79
.67
0.16 0.34 0.17 0.60
.92
0.02 0.50 0.12 1.12
.49
Abbreviations: T1, immediately after surgery; T2, more than 6 months after surgery. Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
group, although there was some resolution after 5 months. The mean blood loss in the MG group (148 140 mL) was significantly less than that in the SG group (284 286 mL; P = .01; Table 5).
likely to occur because of drilling for bicortical screws. The nerve injury probably results from performing BSSO rather than from direct damage from the drill or bicortical screw. However, a case of lingual nerve injury occurred in the SG group. The authors believe that bicortical screws and preparation drilling can directly damage the lingual nerve. In systems using a miniplate with monocortical screw fixation, there is a low risk of damaging the lingual nerve because monocortical screws do not pass through the distal segment. Hence, it has been suggested that bicortical screw fixation systems can cause critical complications, such as lingual nerve injury, compared with miniplate fixation systems, despite the risk of alveolar nerve injury being similar for the 2 systems. Total blood loss was statistically greater in the SG group than in the MG group. In intraoral bicortical screw fixation, the use of a contra-angle handpiece creates some difficulties in controlling drilling and screw placement in the proximal and distal segments simultaneously. In addition, long screws were used in the SG group, whereas short screws were used in the MG group. Hence, intraoral bicortical screw fixation requires wider elevation of the periosteum and stronger pulling of the mucoperiosteal flap to create space compared with intraoral miniplate fixation. Intraoral bicortical screw fixation results in greater surgical stress, and total blood loss has been suggested to be greater than in intraoral miniplate fixation. In general, most bicortical screw fixation systems require extraoral buccal skin incisions using a trocar.4,5
Discussion The purpose of this study was to compare postoperative stability between an intraoral bicortical screw fixation system and an intraoral miniplate with monocortical screw fixation system. The authors hypothesized that the availability of the 2 systems was equal and it was desirable to choose the system depending on the surgeon’s preference. The specific aims of the study were to measure and compare changes in the positions of point B and the Me over time. In the present study, stability changes in point B and the Me were compared between intraoral bicortical screw fixation and miniplate fixation with monocortical screws by an intraoral approach. There was no statistical difference between these systems. There have been some reports on postoperative complications, especially alveolar nerve injury.19,20 The risk of alveolar nerve injury in miniplate fixation systems has been reported to be lower than in bicortical screw fixation systems.19,20 In the present results, there was no statistical difference in inferior alveolar nerve injury between the 2 fixation groups. In the SG group, 3 bicortical screws were placed near the anterior border of the mandibular ramus, which is far from the mandibular canal. Inferior alveolar nerve injury is less
Table 3. CORRELATION BETWEEN CHANGES IN THE POSITION OF POINT B AND EACH INTRAORAL FIXATION GROUP
Group SG (n = 39) MG (n = 36)
Point B on x Axis From T1 to T2 0.17 0.43 0.16 0.53
P Value
Point B on y Axis From T1 to T2
.94
0.02 0.90 0.07 0.82
P Value
.79
Abbreviations: MG, intraoral miniplate with monocortical screw fixation; SG, intraoral bicortical screw fixation; T1, immediately after surgery; T2, more than 6 months after surgery. Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
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Table 4. CORRELATION BETWEEN CHANGES IN THE POSITION OF THE MENTON AND EACH INTRAORAL FIXATION GROUP
Group SG (n = 39) MG (n = 36)
Me at x Axis From T1 to T2 0.26 0.48 0.36 0.68
P Value
Me at y Axis From T1 to T2 0.10 0.61 0.05 0.62
.33
P Value
.77
Abbreviations: Me, menton; MG, intraoral miniplate with monocortical screw fixation; SG, intraoral bicortical screw fixation; T1, immediately after surgery; T2, more than 6 months after surgery. Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
However, because of the esthetic disadvantage, some patients undergoing orthognathic surgery reject a transcutaneous approach.15,21 To avoid skin incision, the authors performed intraoral bicortical screw fixation. Becker et al15 reported that advantages of the intraoral approach include avoiding external skin scars and damage to the mandibular branch of the facial nerve, especially in patients requiring a high level of esthetic satisfaction. Many surgeons have preferred to
use bicortical screw fixation systems, and the use of miniplates with monocortical screws is less frequent in BSSO setback surgery. This is because many surgeons believe that a miniplate with monocortical screw fixation lacks sufficient postoperative stability.3 Some reports have described in vitro biomechanical characteristics by comparing different systems using mandibular replicas.22-24 These reports have indicated that bicortical screw fixation have stronger resistance
FIGURE 3. Amounts of movement at point B and the menton between the 2 intraoral fixation systems. The stability from immediately after surgery to more than 6 months after surgery is shown. A, Point B on x axis. B, Point B on y axis. C, Menton on x axis. D, Menton on y axis. B(X), point Q12 B on x axis; B(Y), point B on y axis; Me(X), menton on x axis; Me(Y), menton on y axis; MG, intraoral miniplate with monocortical screw fixation; NS, not significant; SG, intraoral bicortical screw fixation. Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
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Table 5. CORRELATION BETWEEN EACH INTRAORAL FIXATION GROUP AND OTHER OUTCOME VARIABLES
SG
MG
Postoperative TMD 5 (12.8%) 8 (48.0%) symptoms Inferior alveolar nerve 9 (23.1%) 7 (19.4%) injury Lingual nerve injury 1 (2.6%) 0 (0%) Total blood loss (mL) 284 286 148 140
P Value .22 .78 .52 .01
Abbreviations: MG, intraoral miniplate with monocortical screw fixation; SG, intraoral bicortical screw fixation; TMD, temporomandibular disorder. Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
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against force than miniplate fixation. Sato et al20,21 studied resistance and tension areas created after loading in different fixation systems. They indicated that bicortical screw fixation was more rigid than miniplate fixation. Chuong et al22 reported that deflection at the central incisor and the maximal mechanical response against loading in the distal segments were greater in miniplate fixation using a finite element model. They concluded that 3 bicortical screws resulted in more effective load transmission in the mandibular structure. Similarly, in clinical reports, Fujioka et al25 compared monocortical fixation (miniplates and 4 monocortical screws) with bicortical fixation (2 lag screws) in mandibular setback BSSO. The distal segment of the mandible was rotated clockwise, the proximal segment was rotated counterclockwise, and the mandible was bent at the miniplates. They suggested that bicortical screw fixation was more rigid against loading than monocortical miniplate fixation. Ochs24 concluded that using 3 bicortical screws was the most cost-effective and rigid method, providing a favorable prognosis. However, some recent reports have shown that miniplate fixation stability is equal to that of bicortical screw fixation.8-12,26 Choi et al8,9 suggested that stability was not statistically different more than 24 months after surgery between bicortical screw fixation and a miniplate with monocortical screw fixation. Hsu et al10 concluded that there was no statistical difference in sagittal or vertical changes between bicortical screw fixation and a miniplate with monocortical screw fixation during surgery and during the postoperative period. Therefore, they recommended that surgeons choose the fixation system based on their preference and familiarity with the system. Kabasawa et al11 showed that monocortical fixation using a miniplate system was as reliable as a bicortical screw fixation system, regardless of facial asymmetry. They indicated that the cause of failure was more related to bone quality and surgical technique than to
the fixation system. In fact, Sato et al20,21 showed that Q9 perpendicular screw fixation to a split mandibular ramus provided the best resistance against mechanical stress in their experiment using hemimandibular replicas. Although the results of bicortical screw fixation using mandibular models were acceptable, there were some difficulties in ideal fixation during intraoral bicortical screw fixation using a contra-angle handpiece. In an actual surgical setting, the presence of peripheral soft tissue, especially muscle, disturbs ideal fixation of the mandible. Therefore, some clinical studies, including the present study, might be able to conclude similar stability in the 2 fixation systems.10,11 The major strength of this study is the comparison of screw and miniplate fixation by an intraoral approach. Although several studies have reported comparisons between screw and miniplate fixation, few reports have evaluated intraoral screw fixation systems. There are some weaknesses in this study. First, it was not a prospective, randomized study. Second, the surgical results could not be evaluated by computed tomography. To make up for this limitation, only cases deemed symmetrical on lateral cephalograms were evaluated. In conclusion, there was no statistical difference in stability after BSSO between intraoral bicortical screw fixation and intraoral miniplate with monocortical screw fixation. Considering critical complications, an intraoral miniplate fixation system is useful because of its advantages regarding total blood loss and lingual nerve injury. Taken together, intraoral miniplate with monocortical screw fixation is recommended over intraoral bicortical screw fixation for bone segment fixation in setback BSSO in cases with facial symmetry. Acknowledgments The authors thank their departmental staff and Mr Keishi Shibata for their cooperation in this study.
References 1. Spiessl B: Osteosynthesis in sagittal osteotomy using the Obwegeser-Dal Pont method. Fortschr Kiefer Gesichtschir 18: 145, 1974 (in German) 2. Michelet FX, Benoit JP, Festal F, et al: Fixation without blocking of sagittal osteotomies of the rami by means of endo-buccal screwed plates in the treatment of antero-posterior abnormalities. Rev Stomatol Chir Maxillofac 72:531, 1971 (in French) 3. Joss CU, Vassalli IM: Stability after bilateral sagittal split osteotomy setback surgery with rigid internal fixation: A systematic review. J Oral Maxillofac Surg 66:1634, 2008 4. Danda AK: Comparison of a single noncompression miniplate versus 2 noncompression miniplates in the treatment of mandibular angle fractures: A prospective, randomized clinical trial. J Oral Maxillofac Surg 68:1565, 2010 5. Cole P, Rottgers SA, Cameron H, et al: Improving the minimally invasive approach to mandible angle repair. J Craniofac Surg 19: 525, 2008 6. Farole A: An intraoral technique for transoral rigid fixation of the sagittal split ramus osteotomy. J Oral Maxillofac Surg 50:422, 1992
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7. Kurohara K, Arai N, Nakakuki K, et al: Clinical outcome of orthognathic surgery for the last 12 years in the Department of Maxillofacial Surgery, Tokyo Medical and Dental University. Jpn J Jaw Deform 24:63, 2014 8. Choi BH, Min YS, Yi CK, et al: A comparison of the stability of miniplate with bicortical screw fixation after sagittal split setback. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 90:416, 2000 9. Choi BH, Zhu SJ, Han SG, et al: The need for intermaxillary fixation in sagittal split osteotomy setbacks with bicortical screw fixation. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 100:292, 2005 10. Hsu SS, Huang CS, Chen PK, et al: The stability of mandibular prognathism corrected by bilateral sagittal split osteotomies: A comparison of bi-cortical osteosynthesis and mono-cortical osteosynthesis. Int J Oral Maxillofac Surg 41:142, 2012 11. Kabasawa Y, Sato M, Kikuchi T, et al: Analysis and comparison of clinical results of bilateral sagittal split ramus osteotomy performed with the use of monocortical locking plate fixation or bicortical screw fixation. Oral Surg Oral Med Oral Pathol Oral Radiol 116:e333, 2013 12. Yamashita Y, Otsuka T, Shigematsu M, et al: A long-term comparative study of two rigid internal fixation techniques in terms of masticatory function and neurosensory disturbance after mandibular correction by bilateral sagittal split ramus osteotomy. Int J Oral Maxillofac Surg 40:360, 2011 13. Chung IH, Yoo CK, Lee EK, et al: Postoperative stability after sagittal split ramus osteotomies for a mandibular setback with monocortical plate fixation or bicortical screw fixation. J Oral Maxillofac Surg 66:446, 2008 14. Ellis E III, Esmail N: Malocclusions resulting from loss of fixation after sagittal split ramus osteotomies. J Oral Maxillofac Surg 67: 2528, 2009 15. Becker OE, Avelar RL, Dolzan Ado N, et al: Implant handpiece with adapted drills in orthognathic surgery: Preventing facial scars. J Craniofac Surg 23:e529, 2012 16. Trauner R, Obwegeser H: The surgical correction of mandibular prognathism and retrognathia with consideration of genioplasty.
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24. 25.
26.
II. Operating methods for microgenia and distoclusion. Oral Surg Oral Med Oral Pathol 10:899, 1957 Dal Pont G: Retromolar osteotomy for the correction of prognathism. J Oral Surg Anesth Hosp Dent Serv 19:42, 1961 Harada K, Ono J, Okada Y, et al: Postoperative stability after sagittal split ramus osteotomy with condylar-positioning appliance and screw fixation: Asymmetric versus symmetric cases. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 83:532, 1997 Obwegeser HL: Orthognathic surgery and a tale of how three procedures came to be: A letter to the next generations of surgeons. Clin Plast Surg 34:331, 2007 Sato FR, Asprino L, Consani S, et al: Comparative biomechanical and photoelastic evaluation of different fixation techniques of sagittal split ramus osteotomy in mandibular advancement. J Oral Maxillofac Surg 68:160, 2010 Sato FR, Asprino L, Noritomi PY, et al: Comparison of five different fixation techniques of sagittal split ramus osteotomy using three-dimensional finite elements analysis. Int J Oral Maxillofac Surg 41:934, 2012 Chuong CJ, Borotikar B, Schwartz-Dabney C, et al: Mechanical characteristics of the mandible after bilateral sagittal split ramus osteotomy: Comparing 2 different fixation techniques. J Oral Maxillofac Surg 63:68, 2005 Fujioka M, Fujii T, Hirano A: Comparative study of mandibular stability after sagittal split osteotomies: Biocortical versus monocortical osteosynthesis. Cleft Palate Craniofac J 37:551, 2000 Ochs MW: Bicortical screw stabilization of sagittal split osteotomies. J Oral Maxillofac Surg 61:1477, 2003 Fujioka M, Hirano A, Fujii T: Comparative study of inferior alveolar disturbance restoration after sagittal split osteotomy by means of bicortical versus monocortical osteosynthesis. Plast Reconstr Surg 102:37, 1998 Hu J, Zhao Q, Tang J, et al: Changes in the inferior alveolar nerve following sagittal split ramus osteotomy in monkeys: A comparison of monocortical and bicortical fixation. Br J Oral Maxillofac Surg 45:265, 2007
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CRANIOMAXILLOFACIAL DEFORMITIES/COSMETIC SURGERY
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Does Intraoral Miniplate Fixation Have a Good Postoperative Stability After Sagittal Splitting Ramus Osteotomy? Comparison With Intraoral Bicortical Screw Fixation Yuki Matsushita, DDS, PhD,* Koichi Nakakuki, DDS, PhD,y Machiko Kosugi, DDS,z Kazuto Kurohara, DDS, PhD,x and Kiyoshi Harada, DDS, PhDk Purpose:
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Bicortical screw fixation systems and miniplate with monocortical screw fixation systems have been reported mainly in bilateral sagittal split ramus osteotomy (BSSO). This study compared postoperative stability between these 2 fixation systems by an intraoral approach.
Materials and Methods:
This was a retrospective cohort study. The study sample was composed of patients treated by BSSO at the authors’ institute from January 2006 through December 2012. All cases had facial symmetry and were performed by setback surgery. The predictor variable was treatment group (intraoral screw fixation [SG] vs intraoral miniplate fixation [MG]), and the primary outcome variable was stability defined as the change in the position of point B. Other outcome variables were stability defined as the change in the position of the menton, blood loss, incidence of postoperative temporomandibular joint disorder, and nerve injury. Descriptive and bivariate statistics were computed and the P value was set at .05.
Results:
Seventy-five patients (35 men and 40 women; mean age, 25.8 yr) were divided into 2 groups (39 SG cases and 36 MG cases). Postoperative changes at point B and the menton in the 2 fixation groups were not statistically different. Lingual nerve injury occurred only in SG cases. Moreover, total blood loss was greater in SG cases.
Conclusion:
An intraoral miniplate with monocortical screw fixation system is recommended over intraoral bicortical screw fixation for bone segments in setback BSSO in patients without facial asymmetry. Ó 2015 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg -:1-9, 2015
Bilateral sagittal split ramus osteotomy (BSSO) is a popular surgical procedure for patients with mandibular prognathism. After rigid internal fixation (RIF) systems using bicortical screws or miniplates with monocortical screws were first described in the 1970s,1,2 these
2 fixation systems have been compared for postoperative stability.3 In general, almost all bicortical screw fixation systems need extraoral buccal skin incisions for trocar insertion.4,5 Despite the small wound, some patients worry about esthetic problems
*Research Fellow, Department of Maxillofacial Surgery, Graduate
kProfessor, Department of Maxillofacial Surgery, Graduate School
School of Medical and Dental Sciences, Tokyo Medical and Dental
of Medical and Dental Sciences, Tokyo Medical and Dental
University, Tokyo; Assistant Professor, Department of Clinical Oral
University, Tokyo, Japan.
Oncology, Nagasaki University Graduate School of Biomedical
Address correspondence and reprint requests to Dr Harada:
Sciences, Nagasaki, Japan.
Department of Maxillofacial Surgery, Graduate School of Medical
yAssistant Professor, Department of Maxillofacial Surgery,
and Dental Sciences, Tokyo Medical and Dental University, Tokyo,
Graduate School of Medical and Dental Sciences, Tokyo Medical
113-8549, Japan; e-mail: [email protected]
and Dental University, Tokyo, Japan. zResearch Fellow, Department of Maxillofacial Surgery, Graduate
Received March 12 2015 Accepted June 2 2015
School of Medical and Dental Sciences, Tokyo Medical and Dental
Ó 2015 American Association of Oral and Maxillofacial Surgeons
University, Tokyo, Japan.
0278-2391/15/00816-2
xAssistant Professor, Department of Maxillofacial Surgery,
http://dx.doi.org/10.1016/j.joms.2015.06.148
Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
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FIGURE 1. Two systems for intraoral mandibular fixation. A, Intraoral bicortical screw fixation system. B, Intraoral miniplate with monocortical Q10 screw fixation system. (Fig 1 continued on next page.) Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
because scars sometimes remain. The incidence of external scars after trocar insertion have been reported to be 18%.4 From the early 1990s, intraoral bicortical screw fixation systems have not been reported to cause facial skin scarring or paralysis of the mandibular branch of the facial nerve.6 During the late 1990s, bicortical screw fixation systems by an intraoral approach were adopted at the authors’ institute.7 The authors previously presented the results of desirable stability characteristics of an intraoral bicortical screw fixation system.7 Recently, however, miniplates with monocortical screw fixation systems have been reported to be more stable compared with those used in the past.8-12 One group reported that an intraoral miniplate fixation system was as stable as an extraoral bicortical screw fixation system.13 Moreover, another group indicated that the application of thicker, wider miniplates with monocortical screws had equal durability compared with standard miniplates and bicortical screws.14 However, there are few reports that mention a comparison between intraoral screw and intraoral miniplate fixation systems.15 The purpose of this study was to compare postoperative stability between an intraoral bicortical screw fixation system and an intraoral miniplate with monocortical screw fixation system. The authors hypothe-
sized that the availability of the2 systems were equal and it was desirable to choose the system depending on the surgeon’s preference. The specific aims of the study were to measure and compare changes in the positions of point B and the menton (Me) over time.
Materials and Methods STUDY DESIGN AND SAMPLE
To address the research purpose, the authors designed and implemented a retrospective study. The study population was composed of all patients presenting for evaluation and management of BSSO at the Department of Maxillofacial Surgery, Tokyo Medical and Dental University Hospital (Tokyo, Japan) from January 2006 through December 2012. This study was approved by the Tokyo Medical and Dental University Hospital institutional review board and all participants accepted an informed consent agreement. To be included in the study sample, patients had to fulfill the following inclusion criteria: undergo followup for more than 6 months after surgery, a difference in setback distances between the right and left sides less than 5 mm, surgery performed by 4 surgeons who had acquired familiarity with orthognathic surgery and with more than 10 years of clinical
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FIGURE 1 (cont’d). C, Postoperative radiograph of an intraoral bicortical screw fixation system. (Fig 1 continued on next page.) Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
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experience, and using intraoral bicortical screw fixation or an intraoral miniplate with monocortical screw fixation to fix the 2 fragments. Patients were excluded as study subjects if they had a combination of these 2 fixation systems, absorbable fixation systems, or an extraoral approach using a trocar, had cleft lip or palate, simultaneously underwent genioplasty, or underwent advanced surgery. SURGICAL PROCEDURE
BSSO was performed using methods described previously.16,17 In all cases, condylar positioning devices (CPDs) were applied to reposition the proximal segment when the proximal and distal segments were re-fixed. A miniplate was placed at the anterior
border of the mandibular ramus, the arch bar was fitted to the buccal tube of the upper first molar, and then the arch bar was fixed. Thus, the distance between the mandibular ramus and maxilla was maintained. Using CPDs, bilateral condyles were maintained at their presurgical positions. The incongruity between the proximal and distal segments was eliminated. Even if there were discontinuities between the segments, the segments were fixed to maintain the spacing. The present fixation system by an intraoral approach is shown in Figure 1. Before the 2 segments were fixed, intermaxillary fixation (IMF) was performed. A contra-angle handpiece was inserted intraorally under the periosteum in the 2 groups of patients. In the group that underwent intraoral bicortical screw fixation (SG), 3 bicortical screws were fixed
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FIGURE 1 (cont’d). D, Postoperative radiograph of an intraoral miniplate with monocortical screw fixation system. Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
near the anterior border of the mandibular ramus (Fig 1A, C); in the group that underwent intraoral miniplate with monocortical screw fixation (MG), a 4-hole miniplate was fixed at approximately the same position (Fig 1B, D). After the screws or miniplates were placed, IMF was released. Then, the occlusion was checked and the wound was sutured. VARIABLES
In this study, treatment group (SG vs MG) was set as the primary predictor variable. Stability defined as the change in the position of point B over time was set as the primary outcome variable. Stability defined as the change in the position of the Me over time, blood loss during surgery, incidence of postoperative temporomandibular joint disorder, inferior alveolar nerve
injury, and lingual nerve injury were the secondary outcome variables. Other study variables included age, gender, amount of setback, and the difference in displacement on the right and left sides. DATA COLLECTION METHODS
Lateral cephalograms were analyzed at 3 different time points (before surgery, 5 days after surgery, and >6 months after surgery). The standard x axis was constructed by drawing a line through the sella turcica 6 downward from the line connecting the sella to the nasion.18 The y axis was drawn as a straight line crossing the x axis and passing through the sella turcica. The positions of point B and the Me were measured horizontally and vertically at each time point (Fig 2).
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FIGURE 2. Standard x and y axes and measurement points (point B and the menton) are shown. FH, Frankfurt horizontal; SN, sella and nasion. Q11 Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
DATA ANALYSIS
To compare the pre- and postoperative positions of point B and the Me, the Wilcoxon signed rank test was performed. Measurement values were defined as the mean measured 3 times by 2 measurers.
Results No complication occurred during the perioperative or postoperative period. A total of 131 patients who had undergone BSSO during the study period were reviewed retrospectively. Of these 131 patients, 75 patients who fulfilled the criteria were examined (35 men, 40 women; age range, 18 to 35 yr; average, 25.8 yr). They were divided into 2 different groups according to the RIF system (SG group, 39 patients; MG group, 36 patients). Details of patients in the SG and MG groups are listed in Table 1. In the SG group, the mean amount of setback was 7.4 mm at the right first molar and 7.1 mm at the left first molar, whereas in the MG group, the mean amount of setback was 7.4 mm on the right side and 7.4 mm on the left side. Correlations between changes in the positions of point B and the study variables are presented in Table 2. Changes in the positions of point B and the Me at each time point were measured on lateral cephalograms and are presented in Tables 3 and 4. To examine stability from immediately after surgery to more than 6 months
after surgery, the amounts of movement at point B and the Me between the 2 fixation groups were compared. However, there was no statistical difference between the 2 groups (Fig 3). In the other examinations, 5 patients in the SG group and 8 patients in the MG group reported postoperative temporomandibular disorder symptoms (P = .23). Inferior alveolar nerve injury occurred in the 2 groups and symptoms remained in some of these cases during the follow-up period (SG group, 9 cases; MG group, 7 cases). However, there was no statistical difference between the 2 groups. Lingual nerve injury occurred only in the SG
Table 1. DETAILS OF THE SG AND MG GROUPS
Sample size Men Age (yr) R setback (mm) L setback (mm) Difference (mm)
SG
MG
P Value
39 (52.0%) 24 (61.5%) 25.1 5.9 7.4 2.5 7.1 2.3 2.0 1.8
36 (48.0%) 11 (31.4%) 26.6 9.4 7.4 2.4 7.4 2.5 2.2 1.6
.01 .44 .92 .64 .49
Abbreviations: L, left; MG, intraoral miniplate with monocortical screw fixation; R, right; SG, intraoral bicortical screw fixation. Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
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Table 2. CORRELATION BETWEEN CHANGES IN THE POSITION OF POINT B AND STUDY VARIABLES
Point B on x Axis From T1 to T2 Sample size Gender Men Women Age (yr) #22 (n = 39) $23 (n = 36)
P Value
Point B on y Axis From T1 to T2
75
P Value
75
0.08 0.48 0.23 0.47
.18
0.09 0.93 0.00 0.79
.67
0.16 0.34 0.17 0.60
.92
0.02 0.50 0.12 1.12
.49
Abbreviations: T1, immediately after surgery; T2, more than 6 months after surgery. Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
group, although there was some resolution after 5 months. The mean blood loss in the MG group (148 140 mL) was significantly less than that in the SG group (284 286 mL; P = .01; Table 5).
likely to occur because of drilling for bicortical screws. The nerve injury probably results from performing BSSO rather than from direct damage from the drill or bicortical screw. However, a case of lingual nerve injury occurred in the SG group. The authors believe that bicortical screws and preparation drilling can directly damage the lingual nerve. In systems using a miniplate with monocortical screw fixation, there is a low risk of damaging the lingual nerve because monocortical screws do not pass through the distal segment. Hence, it has been suggested that bicortical screw fixation systems can cause critical complications, such as lingual nerve injury, compared with miniplate fixation systems, despite the risk of alveolar nerve injury being similar for the 2 systems. Total blood loss was statistically greater in the SG group than in the MG group. In intraoral bicortical screw fixation, the use of a contra-angle handpiece creates some difficulties in controlling drilling and screw placement in the proximal and distal segments simultaneously. In addition, long screws were used in the SG group, whereas short screws were used in the MG group. Hence, intraoral bicortical screw fixation requires wider elevation of the periosteum and stronger pulling of the mucoperiosteal flap to create space compared with intraoral miniplate fixation. Intraoral bicortical screw fixation results in greater surgical stress, and total blood loss has been suggested to be greater than in intraoral miniplate fixation. In general, most bicortical screw fixation systems require extraoral buccal skin incisions using a trocar.4,5
Discussion The purpose of this study was to compare postoperative stability between an intraoral bicortical screw fixation system and an intraoral miniplate with monocortical screw fixation system. The authors hypothesized that the availability of the 2 systems was equal and it was desirable to choose the system depending on the surgeon’s preference. The specific aims of the study were to measure and compare changes in the positions of point B and the Me over time. In the present study, stability changes in point B and the Me were compared between intraoral bicortical screw fixation and miniplate fixation with monocortical screws by an intraoral approach. There was no statistical difference between these systems. There have been some reports on postoperative complications, especially alveolar nerve injury.19,20 The risk of alveolar nerve injury in miniplate fixation systems has been reported to be lower than in bicortical screw fixation systems.19,20 In the present results, there was no statistical difference in inferior alveolar nerve injury between the 2 fixation groups. In the SG group, 3 bicortical screws were placed near the anterior border of the mandibular ramus, which is far from the mandibular canal. Inferior alveolar nerve injury is less
Table 3. CORRELATION BETWEEN CHANGES IN THE POSITION OF POINT B AND EACH INTRAORAL FIXATION GROUP
Group SG (n = 39) MG (n = 36)
Point B on x Axis From T1 to T2 0.17 0.43 0.16 0.53
P Value
Point B on y Axis From T1 to T2
.94
0.02 0.90 0.07 0.82
P Value
.79
Abbreviations: MG, intraoral miniplate with monocortical screw fixation; SG, intraoral bicortical screw fixation; T1, immediately after surgery; T2, more than 6 months after surgery. Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
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Table 4. CORRELATION BETWEEN CHANGES IN THE POSITION OF THE MENTON AND EACH INTRAORAL FIXATION GROUP
Group SG (n = 39) MG (n = 36)
Me at x Axis From T1 to T2 0.26 0.48 0.36 0.68
P Value
Me at y Axis From T1 to T2 0.10 0.61 0.05 0.62
.33
P Value
.77
Abbreviations: Me, menton; MG, intraoral miniplate with monocortical screw fixation; SG, intraoral bicortical screw fixation; T1, immediately after surgery; T2, more than 6 months after surgery. Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
However, because of the esthetic disadvantage, some patients undergoing orthognathic surgery reject a transcutaneous approach.15,21 To avoid skin incision, the authors performed intraoral bicortical screw fixation. Becker et al15 reported that advantages of the intraoral approach include avoiding external skin scars and damage to the mandibular branch of the facial nerve, especially in patients requiring a high level of esthetic satisfaction. Many surgeons have preferred to
use bicortical screw fixation systems, and the use of miniplates with monocortical screws is less frequent in BSSO setback surgery. This is because many surgeons believe that a miniplate with monocortical screw fixation lacks sufficient postoperative stability.3 Some reports have described in vitro biomechanical characteristics by comparing different systems using mandibular replicas.22-24 These reports have indicated that bicortical screw fixation have stronger resistance
FIGURE 3. Amounts of movement at point B and the menton between the 2 intraoral fixation systems. The stability from immediately after surgery to more than 6 months after surgery is shown. A, Point B on x axis. B, Point B on y axis. C, Menton on x axis. D, Menton on y axis. B(X), point Q12 B on x axis; B(Y), point B on y axis; Me(X), menton on x axis; Me(Y), menton on y axis; MG, intraoral miniplate with monocortical screw fixation; NS, not significant; SG, intraoral bicortical screw fixation. Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
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Table 5. CORRELATION BETWEEN EACH INTRAORAL FIXATION GROUP AND OTHER OUTCOME VARIABLES
SG
MG
Postoperative TMD 5 (12.8%) 8 (48.0%) symptoms Inferior alveolar nerve 9 (23.1%) 7 (19.4%) injury Lingual nerve injury 1 (2.6%) 0 (0%) Total blood loss (mL) 284 286 148 140
P Value .22 .78 .52 .01
Abbreviations: MG, intraoral miniplate with monocortical screw fixation; SG, intraoral bicortical screw fixation; TMD, temporomandibular disorder. Matsushita et al. Stability of Intraoral Miniplate Fixation. J Oral Maxillofac Surg 2015.
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against force than miniplate fixation. Sato et al20,21 studied resistance and tension areas created after loading in different fixation systems. They indicated that bicortical screw fixation was more rigid than miniplate fixation. Chuong et al22 reported that deflection at the central incisor and the maximal mechanical response against loading in the distal segments were greater in miniplate fixation using a finite element model. They concluded that 3 bicortical screws resulted in more effective load transmission in the mandibular structure. Similarly, in clinical reports, Fujioka et al25 compared monocortical fixation (miniplates and 4 monocortical screws) with bicortical fixation (2 lag screws) in mandibular setback BSSO. The distal segment of the mandible was rotated clockwise, the proximal segment was rotated counterclockwise, and the mandible was bent at the miniplates. They suggested that bicortical screw fixation was more rigid against loading than monocortical miniplate fixation. Ochs24 concluded that using 3 bicortical screws was the most cost-effective and rigid method, providing a favorable prognosis. However, some recent reports have shown that miniplate fixation stability is equal to that of bicortical screw fixation.8-12,26 Choi et al8,9 suggested that stability was not statistically different more than 24 months after surgery between bicortical screw fixation and a miniplate with monocortical screw fixation. Hsu et al10 concluded that there was no statistical difference in sagittal or vertical changes between bicortical screw fixation and a miniplate with monocortical screw fixation during surgery and during the postoperative period. Therefore, they recommended that surgeons choose the fixation system based on their preference and familiarity with the system. Kabasawa et al11 showed that monocortical fixation using a miniplate system was as reliable as a bicortical screw fixation system, regardless of facial asymmetry. They indicated that the cause of failure was more related to bone quality and surgical technique than to
the fixation system. In fact, Sato et al20,21 showed that Q9 perpendicular screw fixation to a split mandibular ramus provided the best resistance against mechanical stress in their experiment using hemimandibular replicas. Although the results of bicortical screw fixation using mandibular models were acceptable, there were some difficulties in ideal fixation during intraoral bicortical screw fixation using a contra-angle handpiece. In an actual surgical setting, the presence of peripheral soft tissue, especially muscle, disturbs ideal fixation of the mandible. Therefore, some clinical studies, including the present study, might be able to conclude similar stability in the 2 fixation systems.10,11 The major strength of this study is the comparison of screw and miniplate fixation by an intraoral approach. Although several studies have reported comparisons between screw and miniplate fixation, few reports have evaluated intraoral screw fixation systems. There are some weaknesses in this study. First, it was not a prospective, randomized study. Second, the surgical results could not be evaluated by computed tomography. To make up for this limitation, only cases deemed symmetrical on lateral cephalograms were evaluated. In conclusion, there was no statistical difference in stability after BSSO between intraoral bicortical screw fixation and intraoral miniplate with monocortical screw fixation. Considering critical complications, an intraoral miniplate fixation system is useful because of its advantages regarding total blood loss and lingual nerve injury. Taken together, intraoral miniplate with monocortical screw fixation is recommended over intraoral bicortical screw fixation for bone segment fixation in setback BSSO in cases with facial symmetry. Acknowledgments The authors thank their departmental staff and Mr Keishi Shibata for their cooperation in this study.
References 1. Spiessl B: Osteosynthesis in sagittal osteotomy using the Obwegeser-Dal Pont method. Fortschr Kiefer Gesichtschir 18: 145, 1974 (in German) 2. Michelet FX, Benoit JP, Festal F, et al: Fixation without blocking of sagittal osteotomies of the rami by means of endo-buccal screwed plates in the treatment of antero-posterior abnormalities. Rev Stomatol Chir Maxillofac 72:531, 1971 (in French) 3. Joss CU, Vassalli IM: Stability after bilateral sagittal split osteotomy setback surgery with rigid internal fixation: A systematic review. J Oral Maxillofac Surg 66:1634, 2008 4. Danda AK: Comparison of a single noncompression miniplate versus 2 noncompression miniplates in the treatment of mandibular angle fractures: A prospective, randomized clinical trial. J Oral Maxillofac Surg 68:1565, 2010 5. Cole P, Rottgers SA, Cameron H, et al: Improving the minimally invasive approach to mandible angle repair. J Craniofac Surg 19: 525, 2008 6. Farole A: An intraoral technique for transoral rigid fixation of the sagittal split ramus osteotomy. J Oral Maxillofac Surg 50:422, 1992
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