Accepted Manuscript A Modified Method of Proximal Segment Alignment after Sagittal Split Ramus Osteotomy for Patients with Mandibular Asymmetry Zhixu Liu, DDS, Shunyao Shen, DDS, MS, James J. Xia, MD, PhD, MS, Xudong Wang, DDS, MD PII:
S0278-2391(15)00503-0
DOI:
10.1016/j.joms.2015.05.003
Reference:
YJOMS 56808
To appear in:
Journal of Oral and Maxillofacial Surgery
Received Date: 10 December 2014 Revised Date:
25 April 2015
Accepted Date: 2 May 2015
Please cite this article as: Liu Z, Shen S, Xia JJ, Wang X, A Modified Method of Proximal Segment Alignment after Sagittal Split Ramus Osteotomy for Patients with Mandibular Asymmetry, Journal of Oral and Maxillofacial Surgery (2015), doi: 10.1016/j.joms.2015.05.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
A Modified Method of Proximal Segment Alignment after Sagittal Split Ramus Osteotomy for Patients
RI PT
with Mandibular Asymmetry Zhixu Liu, DDS1#; Shunyao Shen, DDS, MS1#; James J Xia, MD, PhD, MS2; Xudong Wang, DDS, MD3 1
SC
Resident, Department of Oral and Craniomaxillofacial Surgery, Shanghai Ninth People’s Hospital, Shanghai JiaoTong University School of Medicine; Researcher Assistant, Shanghai Key Laboratory of Stomatology, Shanghai, China. 2
M AN U
Guest Professor, Department of Oral and Craniomaxillofacial Surgery, Shanghai Ninth People’s Hospital, Shanghai JiaoTong University School of Medicine, Shanghai, China; Director of Surgical Planning Laboratory and Professor of Oral and Maxillofacial Surgery, Institute for Academic Medicine, Houston Methodist Hospital, Houston, TX; and Professor of Surgery (Oral and Maxillofacial Surgery), Weill Medicine College, Cornell University, New York, NY 3
#
TE D
Professor and Acting Chair, Department of Oral and Craniomaxillofacial Surgery, Shanghai Ninth People’s Hospital, Shanghai JiaoTong University School of Medicine; Professor, Shanghai Key Laboratory of Stomatology, Shanghai, China. These authors contributed equally to this manuscript.
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Corresponding author Xudong Wang, DDS, MD Department of Oral and Craniomaxillofacial Surgery Shanghai Ninth People’s Hospital Shanghai JiaoTong University School of Medicine 639 Zhi-Zao-Ju Road, Shanghai 200011, China Tel: 86-21-23271699-5143 Email: [email protected] Acknowledgment: This project was supported in part by the National Science Foundation of China (Grant No. 81271122), Top Priority Clinical Medical Center of Shanghai Municipal Commission of Health and Family Planning, Natural Science Foundation of Shanghai Municipal (Grant No. 10ZR1418000), Research Grant of Shanghai Municipal Health Bureau (Grant No. 2009077),
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
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Eastern Scholar at Shanghai Institutions of Higher Education, and Recruitment Program of Global Experts. The author would like to thank radiologists Huimin Shi MD and Qianyang Xie MD for their works in reading MRI images at Shanghai 9th People’s Hospital.
ACCEPTED MANUSCRIPT
A Modified Method of Proximal Segment Alignment after Sagittal Split Ramus Osteotomy
RI PT
for Patients with Mandibular Asymmetry
Abstract: Purpose:
The purpose was to evaluate a modified method of aligning proximal
SC
segment after bilateral sagittal split ramus osteotomy (BSSRO) in the treatment of patients with facial asymmetry.
Patients and Methods: A total of 11 patients with mandibular excess and facial
M AN U
asymmetries were enrolled in this prospective study. The surgery was planned following computer-aided surgical simulation (CASS) protocol. In addition, the proximal segment on the hypoplastic side was intentionally flared out after the distal segment was rotationally setback. If the amount of the gap between the proximal and distal segments was significant, bone grafts were used. The surgery
TE D
was completed following the computerized plan. The proximal segment on the hypoplastic side was fixed with bicortical lag screws, while the proximal segment on the hyperplastic side was fixed with a four-hole mini titanium plate.
EP
Postoperative evaluation was done 6-month after the surgery. Statistical analyses were performed.
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Results: All the surgeries were completed uneventfully. Among 11 patients, 4 also received genioplasty and 3 received bone graft procedure to fill-in the gap and smooth the anterior step. Both doctors and patients satisfied with the surgical outcomes. Only 1 patient received a secondary revision using an onlay hydroxyapatite implant. The results of the statistical analyses showed that the computerized surgical plan could be accurately transferred to the patients at the time of the surgery, and the surgical outcomes achieved with our modified method was better than the routine method of aligning the proximal and distal segments in a maximal contact.
ACCEPTED MANUSCRIPT Conclusion: Our modified method of aligning proximal segment for BSSRO can effectively correct mandibular asymmetry, and reduce the need for a secondary
AC C
EP
TE D
M AN U
SC
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revision surgery.
ACCEPTED MANUSCRIPT
Introduction: It is a challenge to treat patients with mandibular asymmetry, which affects patient’s overall facial symmetry. The paradigm shift of computer-aided surgical simulation (CASS) technology enables surgeons to better plan an orthognathic
RI PT
surgery for patients with severe facial asymmetry in a computer.1, 2 At the time of the surgery, this computerized plan can be transferred to the patient using computer-generated surgical splints and templates.1-8 Unfortunately, even with CASS technology, only the movements of maxilla, mandibular distal segment and
SC
chin can be quantitatively planned and transferred. The placement of proximal segments is still based on a surgeon’s visual judgment. A surgeon traditionally
M AN U
aligns the proximal segment to the mandibular distal segment and places them into a maximal contact. This technique may be acceptable in patients with symmetrical deformity. However, the same may not be true in patients with facial asymmetry.
Mandibular symmetry directly contributes to facial harmony.4 If there is a
TE D
residual asymmetry due to the shape of mandible after an orthognathic surgery, a secondary revision, e.g., bone graft or prosthetic onlay implant, may be required. It is implied that additional surgery causes patient’s additional
EP
discomfort.
It is the authors’ belief that the placement of the proximal segments plays an
AC C
important role in the treatment of patients with facial asymmetry. Therefore, the purpose of this study was to evaluate a modified method of aligning the proximal segment for bilateral sagittal split ramus osteotomy (BSSRO) in the treatment of patients with facial asymmetry. In this method, the proximal segment was intentionally flared out on the hypoplastic side and fixed with 3 bicortical lag screws in a triangular configuration9, while the hyperplastic side was fixed with a surgical mini-plate.
ACCEPTED MANUSCRIPT
Patients and Methods This prospective study was carried out between January 2013 and August 2014. A total of 11 mandibular excess patients with facial asymmetry were enrolled at the clinic of Oral and Craniomaxillofacial Surgery Department at
was 22.1 years (ranged between 18 and 31 years).
RI PT
Shanghai 9th Hospital. Eight were males and 3 were females. Their average age
The patient inclusion criteria for the study were: 1) patients who were diagnosed with mandibular excess and scheduled to undergo an orthognathic
SC
surgery to correct one of the following facial asymmetric deformities: Pogonion deviations >5 mm; asymmetric mandibular angles; or laterognathism; 2) patients
M AN U
who were scheduled to undergo computed tomography (CT) scans before and after the surgery as a part of their treatment protocol; 3) 3D cephalometric analysis showed that it was necessary to increase the bone volume of mandible to correct the mandibular asymmetry; and 4) patients who agreed to participate in the study. The exclusion criteria were 1) syndromic patients; 2) patients who
TE D
suffered from tumors (e.g., ameloblastoma or condylar osteochondroma) or trauma; and 3) patients suffered from systemic diseases which were the contraindication to the orthognathic surgery. This study was approved by the
EP
Shanghai 9th Hospital Institutional Review Board. Prior to the patient enrollment, signed informed consent forms were obtained from all patients.
AC C
Preoperative data acquisition Preoperative CT scan was acquired with a slice thickness of 1.25 mm using a
hospital-based spiral CT scanner. In addition, routine clinical examination was performed. Clinical photographs were taken with a plumbing line hanging on the background when the patient’s head was oriented to the neutral head posture. They were used in conjunction with CASS during the surgical planning process. Although they were not used in planning process, the following examinations for temporomandibular joint (TMJ) were also performed as a part of our routine clinical protocol. Preoperative magnetic resonance imaging (MRI) scans of TMJ
ACCEPTED MANUSCRIPT were acquired and used to set a baseline of TMJ morphology. They were examined by two radiologists. Routine TMJ clinical examination, including interincisor distance, jaw opening / closing / lateral / protrusion motion pattern, joint noise and pain, was also recorded.
RI PT
Surgical planning using CASS technology The surgical planning was carried out in the computer following the CASS protocol6 using a surgical planning software package (ProPlan, Materialise Medical, Leuven, Belgium). The 1st step of the planning process was to generate a
SC
composite skull using the CT data. The resulted composite skull model rendered bony structures and dentition with a high degree of accuracy.
M AN U
The 2nd step was to quantify the deformity. This entailed 3D cephalometric analysis, mirror-imaging method and physical examination to determine the degree of asymmetry.10-13 The reference frame of the head and the midsagittal plane was determined by clinical examination and photographs.6 The 3rd step in the planning process was to simulate the entire surgery in the
TE D
computer. Maxillary LeFort I osteotomy was simulated first, followed by BSSRO, and genioplasty if desired. Only the proximal segment on the hyperplastic side was aligned to the distal segment.
EP
The 4th step in the planning process was to align the proximal segment on the hypoplastic side using mirror-imaging technique (Figure 1). The
AC C
mirror-imaging was created along the midsagittal plane. According to the mirrored image, the proximal segment on the hypoplastic side was aligned to the distal segment until it was matched to the hyperplastic side. This was achievable because the distal segment was rotationally setback and its proximal aspect was rotated toward the hypoplastic side. It is important to note that the proximal segment was only rotated in pitch (swinging anteroposteriorly) and roll (swinging mediolaterally) within a limited range (i.e., within 4° and 3°, respectively). There was no yaw rotation (rotating along the inferosuperior axis) during the proximal segment alignment. If the distal segment kicked the
ACCEPTED MANUSCRIPT proximal segment beyond the above limited range, either the excessed proximal end of the distal segment would be trimmed off or the magnitude of the rotational setback would be reduced. Afterwards, the excessed distal aspect of proximal segment on the hyperplastic side was resected. It was used for the
RI PT
hypoplastic side if the amount of the step between the proximal and distal segments was significant (i.e., beyond 4 mm). In this case, the resected bone segment was split into 2 pieces. One was filled in the gap between the proximal and distal segments on the hypoplastic side. The other was reshaped and onlayed
the mental foramen to smooth the step.
SC
between the anterior aspect of the proximal segment and the posterior aspect of
M AN U
The 5th step in the planning process was to design and fabricate surgical splints. After the surgical simulation was finalized, intermediate and final surgical splints were then designed in the computer and fabricated using a 3D printer (3D System ProJet3510s, 3D Systems, Rock Hill, SC, USA). The printed splints were used at the time of the surgery.
TE D
Finally, a backup surgical plan and dental acrylic splint was created using the traditional planning method, e.g., 2D cephalometric analysis and plaster dental model surgery. This was done as a part of the human subject protection protocol.
EP
Surgical technique
The computerized surgical plan was transferred to the patient at the time of
AC C
surgery following the routine surgical procedure.5 Maxillary surgery was performed first, followed by the mandibular surgery and genioplasty if planned. The computerized intermediate splint was used to position the maxillary segment, and the computerized final splint was used to position the mandibular distal segment. The distal and proximal segments were aligned using our modified method described above. On the hyperplastic side, an ostectomy was performed to remove the excessed distal aspect of the proximal segment as indicated in the CASS plan. The resected bony segment was saved for the hypoplastic side. The
ACCEPTED MANUSCRIPT proximal and distal segments were then fixed using a four-hole mini-titanium plate. On the hypoplastic side, the proximal segment was slightly flared out and aligned to the distal segment based on the CASS plan (Figure 2). Maintaining at
RI PT
this position, the two segments were gently fixed using 3 bicortical lag screws. It is important to note that an excessive force during the fixation should be avoided, especially at the anterior aspect of the proximal segment. This was to maintain the fullness of the mandibular body as planned, as well as to prevent
SC
postoperative temporomandibular disorder due to the unwanted yaw rotation of the proximal segment. If indicated in the surgical plan, the resected bony
M AN U
segments from the hyperplastic side were reshaped, filled into the gap, and onlayed to smooth the step. The onlayed bone graft was fixed using an additional titanium screw.
Postoperative data acquisition
All postoperative data were collected 6 months after the surgery.
TE D
Postoperative CT scans were acquired using the same scanning protocol while the upper and lower teeth were placed in maximal intercuspation. They were used to evaluate the surgical outcomes. In addition, postoperative MRI scans of
EP
TMJ were acquired to evaluate any possible morphological and positional changes of condyle and disk based on our clinical protocol. The same clinical
AC C
examination of TMJ was also performed. They were also used to detect any changes in symptoms of temporomandibular disorder. The same 2 radiologists who were blinded from the patient’s surgical history again evaluated the MRI images.
Data analysis Postoperative 3D midface and mandibular CT models were generated for each patient. The postoperative models were superimposed to the planned model by aligning surgically unaltered volumes, i.e., cranium and midface above Le Fort I osteotomy line.5
ACCEPTED MANUSCRIPT After the postoperative CT models were registered, 7 anatomical landmarks were digitized on the original, planned and postoperative mandibles by a single examiner (Z.L.) who was not involved in the original surgical planning. They were menton, right and left MPP3 on the distal segment, and right and left MPP7 and
RI PT
gonion in the proximal segments (Table 1 and Figure 3). The method of the landmark digitization was based on a published report5. After that, the landmarks of MPP7 and gonion were digitally “glued” onto the planned proximal segments, which were then reset to their original unaligned positions. The distal
SC
segment remained static at the planned position. A second examiner (S.S.), who was experienced in orthognathic surgery but also not involved in the original
M AN U
planning, realigned the proximal segments to the distal segment following the routine procedure of making a maximal contact between them. The coordinates of each landmark were recorded, paired and tabulated in an Excel spreadsheet. For the purpose of easy presentation, the landmarks on the hypoplastic side were normalized to the right, and the landmarks on the
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hyperplastic side were normalized to the left. The differences (deltas) of paired coordinates between the hypoplastic and hyperplastic sides were then computed in mediolateral (x), anteroposterior (y) and inferosuperior (z) directions,
EP
respectively. In addition, Asymmetry Index for each paired landmarks (MPP3, MPP6 and gonion) in mediolateral direction was calculated using the following
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equation:
=
( ) − ( ) × 100% ( ) + ( )
where represents the x-coordinate on the hypoplastic side, while represents the x-coordinate on the hyperplastic side. All date were checked and found normally distributed. Mean and 95% of confidence interval (95% CI) were calculated. A step-wise statistical approach was used. The 1st step was to detect whether the CASS plan could be accurately transferred at the time of the surgery. The planned outcome was compared to the postoperative outcome. Intraclass correlation coefficients (ICCs) with absolute
ACCEPTED MANUSCRIPT agreement definition were used. The variables were the paired x, y and z coordinates of each landmark between the planned and postoperative outcomes. The 2nd step was to detect whether there was a significant reduction in asymmetry after the surgery. A repeated measures analysis of variance (ANOVA)
RI PT
was used. The response variable was the delta. The within factors were 2 status (preoperative condition and postoperative outcome), 3 directions (x, y and z), and 4 landmarks (menton, MPP3, MPP7 and gonion). If statistically significant, within contract would be further computed. Finally, the 3rd step was to detect
SC
whether our method of aligning proximal segment could achieve better mandibular symmetry mediolaterally. A repeated measures ANOVA was used
M AN U
again. The response variable was the delta in x-axis. The within factors were 2 status (postoperative outcome and the outcome achieved with hypothetic routine alignment) and 2 landmarks (MPP7 and gonion). If statistically significant,
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within contract would be further computed.
ACCEPTED MANUSCRIPT
Results All the surgeries were completed uneventfully by a single surgeon (X.W.). The backup splints were never used. Six-month postoperative CT showed the proximal and distal segments healed normally on both sides of the mandible.
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Postoperative patient physical examination showed no change in interincisal distance, jaw motion pattern and joint noise 6 months after the surgery. Six-month postoperative MRI also showed no evidence of morphological and positional changes in the disk and condyle (Figure 4).
SC
Among 11 patients, 4 received genioplasty and 3 received bone graft procedure to fill-in the gap and smooth the step at the same time of the
M AN U
orthognathic surgery. Only 1 patient had a severe residual vertical deficiency in mandibular gonial angle and further received a secondary revision surgery using an onlay hydroxyapatite implant.
The means and 95% of CI of the difference and Asymmetry Index between the hypoplastic and hyperplastic sides are presented in Tables 2 and 3, respectively.
agreement
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The results of the 1st step in statistics showed a high degree of absolute between
the
planned
and
the
postoperative
outcomes
(ICC=0.926-0.999). It indicated that both distal and proximal segments could be
EP
accurately positioned at the time of the surgery following the CASS plan. The result of repeated measures ANOVA in the 2nd step showed there was a
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statistically significant difference between the original condition and the postoperative outcomes [F(1,10)=25.04, P
S0278-2391(15)00503-0
DOI:
10.1016/j.joms.2015.05.003
Reference:
YJOMS 56808
To appear in:
Journal of Oral and Maxillofacial Surgery
Received Date: 10 December 2014 Revised Date:
25 April 2015
Accepted Date: 2 May 2015
Please cite this article as: Liu Z, Shen S, Xia JJ, Wang X, A Modified Method of Proximal Segment Alignment after Sagittal Split Ramus Osteotomy for Patients with Mandibular Asymmetry, Journal of Oral and Maxillofacial Surgery (2015), doi: 10.1016/j.joms.2015.05.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
A Modified Method of Proximal Segment Alignment after Sagittal Split Ramus Osteotomy for Patients
RI PT
with Mandibular Asymmetry Zhixu Liu, DDS1#; Shunyao Shen, DDS, MS1#; James J Xia, MD, PhD, MS2; Xudong Wang, DDS, MD3 1
SC
Resident, Department of Oral and Craniomaxillofacial Surgery, Shanghai Ninth People’s Hospital, Shanghai JiaoTong University School of Medicine; Researcher Assistant, Shanghai Key Laboratory of Stomatology, Shanghai, China. 2
M AN U
Guest Professor, Department of Oral and Craniomaxillofacial Surgery, Shanghai Ninth People’s Hospital, Shanghai JiaoTong University School of Medicine, Shanghai, China; Director of Surgical Planning Laboratory and Professor of Oral and Maxillofacial Surgery, Institute for Academic Medicine, Houston Methodist Hospital, Houston, TX; and Professor of Surgery (Oral and Maxillofacial Surgery), Weill Medicine College, Cornell University, New York, NY 3
#
TE D
Professor and Acting Chair, Department of Oral and Craniomaxillofacial Surgery, Shanghai Ninth People’s Hospital, Shanghai JiaoTong University School of Medicine; Professor, Shanghai Key Laboratory of Stomatology, Shanghai, China. These authors contributed equally to this manuscript.
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Corresponding author Xudong Wang, DDS, MD Department of Oral and Craniomaxillofacial Surgery Shanghai Ninth People’s Hospital Shanghai JiaoTong University School of Medicine 639 Zhi-Zao-Ju Road, Shanghai 200011, China Tel: 86-21-23271699-5143 Email: [email protected] Acknowledgment: This project was supported in part by the National Science Foundation of China (Grant No. 81271122), Top Priority Clinical Medical Center of Shanghai Municipal Commission of Health and Family Planning, Natural Science Foundation of Shanghai Municipal (Grant No. 10ZR1418000), Research Grant of Shanghai Municipal Health Bureau (Grant No. 2009077),
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
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Eastern Scholar at Shanghai Institutions of Higher Education, and Recruitment Program of Global Experts. The author would like to thank radiologists Huimin Shi MD and Qianyang Xie MD for their works in reading MRI images at Shanghai 9th People’s Hospital.
ACCEPTED MANUSCRIPT
A Modified Method of Proximal Segment Alignment after Sagittal Split Ramus Osteotomy
RI PT
for Patients with Mandibular Asymmetry
Abstract: Purpose:
The purpose was to evaluate a modified method of aligning proximal
SC
segment after bilateral sagittal split ramus osteotomy (BSSRO) in the treatment of patients with facial asymmetry.
Patients and Methods: A total of 11 patients with mandibular excess and facial
M AN U
asymmetries were enrolled in this prospective study. The surgery was planned following computer-aided surgical simulation (CASS) protocol. In addition, the proximal segment on the hypoplastic side was intentionally flared out after the distal segment was rotationally setback. If the amount of the gap between the proximal and distal segments was significant, bone grafts were used. The surgery
TE D
was completed following the computerized plan. The proximal segment on the hypoplastic side was fixed with bicortical lag screws, while the proximal segment on the hyperplastic side was fixed with a four-hole mini titanium plate.
EP
Postoperative evaluation was done 6-month after the surgery. Statistical analyses were performed.
AC C
Results: All the surgeries were completed uneventfully. Among 11 patients, 4 also received genioplasty and 3 received bone graft procedure to fill-in the gap and smooth the anterior step. Both doctors and patients satisfied with the surgical outcomes. Only 1 patient received a secondary revision using an onlay hydroxyapatite implant. The results of the statistical analyses showed that the computerized surgical plan could be accurately transferred to the patients at the time of the surgery, and the surgical outcomes achieved with our modified method was better than the routine method of aligning the proximal and distal segments in a maximal contact.
ACCEPTED MANUSCRIPT Conclusion: Our modified method of aligning proximal segment for BSSRO can effectively correct mandibular asymmetry, and reduce the need for a secondary
AC C
EP
TE D
M AN U
SC
RI PT
revision surgery.
ACCEPTED MANUSCRIPT
Introduction: It is a challenge to treat patients with mandibular asymmetry, which affects patient’s overall facial symmetry. The paradigm shift of computer-aided surgical simulation (CASS) technology enables surgeons to better plan an orthognathic
RI PT
surgery for patients with severe facial asymmetry in a computer.1, 2 At the time of the surgery, this computerized plan can be transferred to the patient using computer-generated surgical splints and templates.1-8 Unfortunately, even with CASS technology, only the movements of maxilla, mandibular distal segment and
SC
chin can be quantitatively planned and transferred. The placement of proximal segments is still based on a surgeon’s visual judgment. A surgeon traditionally
M AN U
aligns the proximal segment to the mandibular distal segment and places them into a maximal contact. This technique may be acceptable in patients with symmetrical deformity. However, the same may not be true in patients with facial asymmetry.
Mandibular symmetry directly contributes to facial harmony.4 If there is a
TE D
residual asymmetry due to the shape of mandible after an orthognathic surgery, a secondary revision, e.g., bone graft or prosthetic onlay implant, may be required. It is implied that additional surgery causes patient’s additional
EP
discomfort.
It is the authors’ belief that the placement of the proximal segments plays an
AC C
important role in the treatment of patients with facial asymmetry. Therefore, the purpose of this study was to evaluate a modified method of aligning the proximal segment for bilateral sagittal split ramus osteotomy (BSSRO) in the treatment of patients with facial asymmetry. In this method, the proximal segment was intentionally flared out on the hypoplastic side and fixed with 3 bicortical lag screws in a triangular configuration9, while the hyperplastic side was fixed with a surgical mini-plate.
ACCEPTED MANUSCRIPT
Patients and Methods This prospective study was carried out between January 2013 and August 2014. A total of 11 mandibular excess patients with facial asymmetry were enrolled at the clinic of Oral and Craniomaxillofacial Surgery Department at
was 22.1 years (ranged between 18 and 31 years).
RI PT
Shanghai 9th Hospital. Eight were males and 3 were females. Their average age
The patient inclusion criteria for the study were: 1) patients who were diagnosed with mandibular excess and scheduled to undergo an orthognathic
SC
surgery to correct one of the following facial asymmetric deformities: Pogonion deviations >5 mm; asymmetric mandibular angles; or laterognathism; 2) patients
M AN U
who were scheduled to undergo computed tomography (CT) scans before and after the surgery as a part of their treatment protocol; 3) 3D cephalometric analysis showed that it was necessary to increase the bone volume of mandible to correct the mandibular asymmetry; and 4) patients who agreed to participate in the study. The exclusion criteria were 1) syndromic patients; 2) patients who
TE D
suffered from tumors (e.g., ameloblastoma or condylar osteochondroma) or trauma; and 3) patients suffered from systemic diseases which were the contraindication to the orthognathic surgery. This study was approved by the
EP
Shanghai 9th Hospital Institutional Review Board. Prior to the patient enrollment, signed informed consent forms were obtained from all patients.
AC C
Preoperative data acquisition Preoperative CT scan was acquired with a slice thickness of 1.25 mm using a
hospital-based spiral CT scanner. In addition, routine clinical examination was performed. Clinical photographs were taken with a plumbing line hanging on the background when the patient’s head was oriented to the neutral head posture. They were used in conjunction with CASS during the surgical planning process. Although they were not used in planning process, the following examinations for temporomandibular joint (TMJ) were also performed as a part of our routine clinical protocol. Preoperative magnetic resonance imaging (MRI) scans of TMJ
ACCEPTED MANUSCRIPT were acquired and used to set a baseline of TMJ morphology. They were examined by two radiologists. Routine TMJ clinical examination, including interincisor distance, jaw opening / closing / lateral / protrusion motion pattern, joint noise and pain, was also recorded.
RI PT
Surgical planning using CASS technology The surgical planning was carried out in the computer following the CASS protocol6 using a surgical planning software package (ProPlan, Materialise Medical, Leuven, Belgium). The 1st step of the planning process was to generate a
SC
composite skull using the CT data. The resulted composite skull model rendered bony structures and dentition with a high degree of accuracy.
M AN U
The 2nd step was to quantify the deformity. This entailed 3D cephalometric analysis, mirror-imaging method and physical examination to determine the degree of asymmetry.10-13 The reference frame of the head and the midsagittal plane was determined by clinical examination and photographs.6 The 3rd step in the planning process was to simulate the entire surgery in the
TE D
computer. Maxillary LeFort I osteotomy was simulated first, followed by BSSRO, and genioplasty if desired. Only the proximal segment on the hyperplastic side was aligned to the distal segment.
EP
The 4th step in the planning process was to align the proximal segment on the hypoplastic side using mirror-imaging technique (Figure 1). The
AC C
mirror-imaging was created along the midsagittal plane. According to the mirrored image, the proximal segment on the hypoplastic side was aligned to the distal segment until it was matched to the hyperplastic side. This was achievable because the distal segment was rotationally setback and its proximal aspect was rotated toward the hypoplastic side. It is important to note that the proximal segment was only rotated in pitch (swinging anteroposteriorly) and roll (swinging mediolaterally) within a limited range (i.e., within 4° and 3°, respectively). There was no yaw rotation (rotating along the inferosuperior axis) during the proximal segment alignment. If the distal segment kicked the
ACCEPTED MANUSCRIPT proximal segment beyond the above limited range, either the excessed proximal end of the distal segment would be trimmed off or the magnitude of the rotational setback would be reduced. Afterwards, the excessed distal aspect of proximal segment on the hyperplastic side was resected. It was used for the
RI PT
hypoplastic side if the amount of the step between the proximal and distal segments was significant (i.e., beyond 4 mm). In this case, the resected bone segment was split into 2 pieces. One was filled in the gap between the proximal and distal segments on the hypoplastic side. The other was reshaped and onlayed
the mental foramen to smooth the step.
SC
between the anterior aspect of the proximal segment and the posterior aspect of
M AN U
The 5th step in the planning process was to design and fabricate surgical splints. After the surgical simulation was finalized, intermediate and final surgical splints were then designed in the computer and fabricated using a 3D printer (3D System ProJet3510s, 3D Systems, Rock Hill, SC, USA). The printed splints were used at the time of the surgery.
TE D
Finally, a backup surgical plan and dental acrylic splint was created using the traditional planning method, e.g., 2D cephalometric analysis and plaster dental model surgery. This was done as a part of the human subject protection protocol.
EP
Surgical technique
The computerized surgical plan was transferred to the patient at the time of
AC C
surgery following the routine surgical procedure.5 Maxillary surgery was performed first, followed by the mandibular surgery and genioplasty if planned. The computerized intermediate splint was used to position the maxillary segment, and the computerized final splint was used to position the mandibular distal segment. The distal and proximal segments were aligned using our modified method described above. On the hyperplastic side, an ostectomy was performed to remove the excessed distal aspect of the proximal segment as indicated in the CASS plan. The resected bony segment was saved for the hypoplastic side. The
ACCEPTED MANUSCRIPT proximal and distal segments were then fixed using a four-hole mini-titanium plate. On the hypoplastic side, the proximal segment was slightly flared out and aligned to the distal segment based on the CASS plan (Figure 2). Maintaining at
RI PT
this position, the two segments were gently fixed using 3 bicortical lag screws. It is important to note that an excessive force during the fixation should be avoided, especially at the anterior aspect of the proximal segment. This was to maintain the fullness of the mandibular body as planned, as well as to prevent
SC
postoperative temporomandibular disorder due to the unwanted yaw rotation of the proximal segment. If indicated in the surgical plan, the resected bony
M AN U
segments from the hyperplastic side were reshaped, filled into the gap, and onlayed to smooth the step. The onlayed bone graft was fixed using an additional titanium screw.
Postoperative data acquisition
All postoperative data were collected 6 months after the surgery.
TE D
Postoperative CT scans were acquired using the same scanning protocol while the upper and lower teeth were placed in maximal intercuspation. They were used to evaluate the surgical outcomes. In addition, postoperative MRI scans of
EP
TMJ were acquired to evaluate any possible morphological and positional changes of condyle and disk based on our clinical protocol. The same clinical
AC C
examination of TMJ was also performed. They were also used to detect any changes in symptoms of temporomandibular disorder. The same 2 radiologists who were blinded from the patient’s surgical history again evaluated the MRI images.
Data analysis Postoperative 3D midface and mandibular CT models were generated for each patient. The postoperative models were superimposed to the planned model by aligning surgically unaltered volumes, i.e., cranium and midface above Le Fort I osteotomy line.5
ACCEPTED MANUSCRIPT After the postoperative CT models were registered, 7 anatomical landmarks were digitized on the original, planned and postoperative mandibles by a single examiner (Z.L.) who was not involved in the original surgical planning. They were menton, right and left MPP3 on the distal segment, and right and left MPP7 and
RI PT
gonion in the proximal segments (Table 1 and Figure 3). The method of the landmark digitization was based on a published report5. After that, the landmarks of MPP7 and gonion were digitally “glued” onto the planned proximal segments, which were then reset to their original unaligned positions. The distal
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segment remained static at the planned position. A second examiner (S.S.), who was experienced in orthognathic surgery but also not involved in the original
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planning, realigned the proximal segments to the distal segment following the routine procedure of making a maximal contact between them. The coordinates of each landmark were recorded, paired and tabulated in an Excel spreadsheet. For the purpose of easy presentation, the landmarks on the hypoplastic side were normalized to the right, and the landmarks on the
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hyperplastic side were normalized to the left. The differences (deltas) of paired coordinates between the hypoplastic and hyperplastic sides were then computed in mediolateral (x), anteroposterior (y) and inferosuperior (z) directions,
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respectively. In addition, Asymmetry Index for each paired landmarks (MPP3, MPP6 and gonion) in mediolateral direction was calculated using the following
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equation:
=
( ) − ( ) × 100% ( ) + ( )
where represents the x-coordinate on the hypoplastic side, while represents the x-coordinate on the hyperplastic side. All date were checked and found normally distributed. Mean and 95% of confidence interval (95% CI) were calculated. A step-wise statistical approach was used. The 1st step was to detect whether the CASS plan could be accurately transferred at the time of the surgery. The planned outcome was compared to the postoperative outcome. Intraclass correlation coefficients (ICCs) with absolute
ACCEPTED MANUSCRIPT agreement definition were used. The variables were the paired x, y and z coordinates of each landmark between the planned and postoperative outcomes. The 2nd step was to detect whether there was a significant reduction in asymmetry after the surgery. A repeated measures analysis of variance (ANOVA)
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was used. The response variable was the delta. The within factors were 2 status (preoperative condition and postoperative outcome), 3 directions (x, y and z), and 4 landmarks (menton, MPP3, MPP7 and gonion). If statistically significant, within contract would be further computed. Finally, the 3rd step was to detect
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whether our method of aligning proximal segment could achieve better mandibular symmetry mediolaterally. A repeated measures ANOVA was used
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again. The response variable was the delta in x-axis. The within factors were 2 status (postoperative outcome and the outcome achieved with hypothetic routine alignment) and 2 landmarks (MPP7 and gonion). If statistically significant,
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within contract would be further computed.
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Results All the surgeries were completed uneventfully by a single surgeon (X.W.). The backup splints were never used. Six-month postoperative CT showed the proximal and distal segments healed normally on both sides of the mandible.
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Postoperative patient physical examination showed no change in interincisal distance, jaw motion pattern and joint noise 6 months after the surgery. Six-month postoperative MRI also showed no evidence of morphological and positional changes in the disk and condyle (Figure 4).
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Among 11 patients, 4 received genioplasty and 3 received bone graft procedure to fill-in the gap and smooth the step at the same time of the
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orthognathic surgery. Only 1 patient had a severe residual vertical deficiency in mandibular gonial angle and further received a secondary revision surgery using an onlay hydroxyapatite implant.
The means and 95% of CI of the difference and Asymmetry Index between the hypoplastic and hyperplastic sides are presented in Tables 2 and 3, respectively.
agreement
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The results of the 1st step in statistics showed a high degree of absolute between
the
planned
and
the
postoperative
outcomes
(ICC=0.926-0.999). It indicated that both distal and proximal segments could be
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accurately positioned at the time of the surgery following the CASS plan. The result of repeated measures ANOVA in the 2nd step showed there was a
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statistically significant difference between the original condition and the postoperative outcomes [F(1,10)=25.04, P
