- Email: [email protected]
Preservation of the inferior alveolar neurovascular bundle in the osteotomy of benign lesions of the mandible using a digital template
YBJOM-4503; No. of Pages 5
ARTICLE IN PRESS Available online at www.sciencedirect.com
British Journal of Oral and Maxillofacial Surgery xxx (2015) xxx–xxx
Preservation of the inferior alveolar neurovascular bundle in the osteotomy of benign lesions of the mandible using a digital template夽 Dong Huang a,1 , MinJie Chen a,1 , DongMei He a,∗ , Chi Yang a,∗∗ , JianBing Yuan b , Guo Bai b , YiWen Wang a , WenBin Wei a , ZhuoZhi Chen a a
Department of Oral Surgery, Shanghai Ninth People’s Hospital, College of Stomatology, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai, China b School of Mechanical and Power Engineering, Shanghai Jiao Tong University. Shanghai, China Accepted 13 April 2015
Abstract Our aim was to evaluate the effect of a digital template in the preservation of the inferior alveolar neurovascular bundle during osteotomy for benign lesions of the mandible in 6 patients who were treated with mandibular osteotomies during 2013. Computed tomographic (CT) data were imported into ProPlan CMF 1.4 software. The borders of the lesion and the inferior alveolar canal were marked, and a digital template designed to mark the borders, outline the canal, and guide the osteotomy. A mirror image of the unaffected mandible was used to make a stereolithographic model by a rapid prototyping technique to prefabricate the reconstruction plate for the bone graft. The accuracy of the designs and the templates was evaluated during operation and postoperatively by CT. The sensation of the skin was tested using a Neurometer® CPT (current perception threshold) sensory detector (Neurotron Inc, Baltimore USA) to evaluate the function of the preserved inferior alveolar neurovascular bundle during follow up. With the digital template it was possible to guide removal of the bony lesion while accurately protecting the neurovascular bundle. Follow up for a mean of 8 months (range 5 -12) showed good facial symmetry, a stable occlusion, and recovery of sensation in the lower lip on the affected side. We conclude that a digital template can successfully help the resection of benign lesions of the mandible while preserving the function of the inferior alveolar neurovascular bundle. © 2015 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Keywords: Digital template; Inferior alveolar neurovascular bundle; Mandibular Benign Lesions; Mandible reconstruction
夽 This research was supported by Research Fund of Science and Technology Commission of Shanghai Municipality (08DZ2271100, 13XD1402300) and Research Fund of Biomedicine Engineering of Shanghai JiaoTong University (YG2009MS42). ∗ Corresponding author at: Department of Oral Surgery, Shanghai Ninth People’s Hospital, College of stomatology, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology. No. 639, Zhi Zao Ju Road, Shanghai, China. Tel.: +86 21 3271699 5707. ∗∗ Corresponding author at: Department of Oral Surgery, Shanghai Ninth People’s Hospital, College of stomatology, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology. No. 639, Zhi Zao Ju Road, Shanghai, China. Tel: +86 21 3271699 5218. E-mail addresses: [email protected] (D. He),[email protected] (C. Yang). 1 Authors D.H and M.C contributed equally to this work.
http://dx.doi.org/10.1016/j.bjoms.2015.04.013 0266-4356/© 2015 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Huang D, et al. Preservation of the inferior alveolar neurovascular bundle in the osteotomy of benign lesions of the mandible using a digital template. Br J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.bjoms.2015.04.013
YBJOM-4503; No. of Pages 5
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ARTICLE IN PRESS D. Huang et al. / British Journal of Oral and Maxillofacial Surgery xxx (2015) xxx–xxx
Introduction
Table 1 Details of the patients.
Ossifying fibroma, osteomyelitis, and fibrous dysplasia are examples of common benign lesions in the mandible. They can present with swelling, facial asymmetry, and in some patients, infection.1–3 The most common treatments are curettage, mandibular contouring and, in severe cases, partial mandibulectomy with reconstruction may be necessary. However, the inferior alveolar neurovascular bundle, which controls the sensation of the skin of the lower lip and chin, may be jeopardised during operation and this can result in postoperative numbness of the lower lip and chin.1–3 Some authors have reported successful preservation of the neurovascular bundle, which improved patients’ quality of life after operation.1–3 However, the disadvantages of these studies were that they used only conventional plain radiographs or computed tomographic (CT) images to trace the path of the inferior alveolar canal preoperatively, and did not describe an effective way to transfer the osteotomy plan and design into a live procedure, so precision was not possible. In recent years, computer-aided surgical techniques have been more widely used in oral and maxillofacial surgery, including 3-dimensional cephalometry, surgical design and simulation, CAD/CAM digital osteotomy templates, intraoperative navigation, and postoperative evaluation.4 Some authors have reported the use of computer-aided techniques in the treatment of mandibular benign lesions including for design of the osteotomy plane and production of digital osteotomy templates, and design and production of templates for remodelling and grafting bone.5,6 The intraoperative use of all types of templates can greatly improve the accuracy of resection and reconstruction, reduce operating time and the degree of trauma, and improve postoperative facial symmetry and aesthetics.5–8 However, to our knowledge the preservation of the inferior alveolar neurovascular bundle with the help of digital template has not been reported so far. We describe here how we fabricated a digital template by computer-assisted techniques to help us mark the borders of the lesion and outline the inferior alveolar canal during osteotomy to preserve the neurovascular bundle and to maintain its sensory function. We evaluated the accuracy of the technique and the template during and after operation on CT images, and the nerve function during follow up with a Neurometer® CPT (current perception threshold) sensory detector (Neurotron Inc, Baltimore, USA).
Case No
Sex
Age (years)
Affected side
Diagnosis
1 2 3 4 5 6
Male Male Female Female Female Female
18 28 20 37 18 44
Right Left Left Right Left Right
Ossifying fibroma Fibrous dysplasia Fibrous dysplasia Ossifying fibroma Osteomyelitis Osteomyelitis
All patients except case 5 had a costochondral graft through preauricular and submandibular approaches. Case 5 had an iliac bone graft through preauricular and intraoral approaches.
mandible, but in each case the inferior alveolar canal was unaffected compared with the opposite side. Plan of treatment and fabrication of the digital template Three-dimensional reconstruction of the inferior alveolar canal: data from a thin-layer CT scan (0.625 mm) were imported into ProPlan CMF 1.4 software (Materialize, Leuven, Belgium) in DICOM format, followed by 3-dimensional reconstruction and segmentation of the maxilla and mandible. The inferior alveolar canal was traced and marked from the mental foramen to the mandibular uvula in coronal layers, and then the 3-dimensional image of the canal was reconstructed (Fig. 1). Design of the osteotomy and template to preserve the nerve: the mandible was shown as transparent to show the inferior alveolar canal. The osteotomy planes were designed within the normal bone, just below the projection of the canal on the surface of the bone. Segments of bone were resected and the canal preserved. Marks were made on the osteotomy plane to show the measured depth of the canal, which guided the intraoperative separation of the inferior alveolar neurovascular bundle (Fig. 1). A digital template for the osteotomy with preservation of the nerve was then designed, with the upper edge indicating the osteotomy plane and the border of the lesion, and the lower edge surrounding the mandibular
Patients and Methods Patients with benign mandibular lesions that were treated by mandibular osteotomy and bone grafting for reconstruction during 2013 were included in the study (Table 1). On clinical examination all patients had facial asymmetry, together with obvious swelling of the mandible on the affected side but no numbness of the chin and lip. CT showed considerable swelling and bony changes in the affected
Fig. 1. Three-dimensional reconstruction of the inferior alveolar canal and design of the osteotomy plane. The numbers indicate the depth of the inferior alveolar canal at each marked point (mm).
Please cite this article in press as: Huang D, et al. Preservation of the inferior alveolar neurovascular bundle in the osteotomy of benign lesions of the mandible using a digital template. Br J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.bjoms.2015.04.013
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Fig. 3. Separation and protection of the inferior alveolar neurovascular bundle (yellow arrow).
plates in accordance with the model of the mirror image after intermaxillary fixation. Evaluation of outcome postoperatively
Fig. 2. A = design of the digital template according to computed tomographic data and the osteotomy design. B= use of the digital template during the operation.
Postoperative CT data were imported into the software, and facial symmetry evaluated by measuring the distance from the mandibular angle point to the middle sagittal plane. During follow up the Neurometer® CPT (current perception threshold) sensory detector was used to evaluate the sensation of the skin of the chin and the lower lip, and the difference between the two sides was calculated to assess the function of the inferior alveolar neurovascular bundle.
body and ramus (Fig. 2A). A mirror image was taken of the unaffected mandible in the midsagittal plane, and a model made using a rapid prototyping technique to prefabricate the titanium reconstruction plate. Fabrication of the digital template: the design of the osteotomy templates was exported as stereolithographic files, which were then imported into a rapid prototyping machine to manufacture the digital templates (Shanghai JiaoTong University School of Mechanical and Power Engineering). The templates were then sterilised with plasma for surgical use.
Statistical analysis
Intraoperative use of the digital templates
Six patients were included in this study (Table 1). Details of the operations and follow up are shown in Table 2. The digital templates fitted well on the mandibular surface, and no nerve damage was found during surgery. Postoperative CT showed that the mandibular lesions had been removed completely. Distances from the mandibular angle point to the midsagittal plane on the reconstructed side did not differ significantly from those on the unaffected side (p = 0.90) (Table 2).
All patients had their lesions resected under general anaesthesia followed by mandibular reconstruction by either costochondral graft or iliac bone graft through a modified preauricular 9 and submandibular approach (except case 5 when we used an intraoral approach) (Table 1). Mandibular osteotomies were made according to the digital template to mark the borders of the lesion. A careful cut was made along the upper border of the template, indicating the trajectory of the inferior alveolar canal, according to the depth measured preoperatively from the buccal bone surface to the canal itself (Fig. 2B). The neurovascular bundle was then separated and protected (Fig. 3). Bone grafts were harvested to reconstruct the resected mandible and fixed by the prefabricated
The Go-MSP distances on both sides and values for current perception thresholds during follow up were assessed using a paired t test, and probabilities of less than 0.05 were accepted as significant. For all statistical analyses we use SPSS 17.0 (version 17, SPSS Inc, Chicago, USA) software.
Results
Discussion Because we created patient-specific templates to protect the nerve during operations for benign lesions of the mandible,
Please cite this article in press as: Huang D, et al. Preservation of the inferior alveolar neurovascular bundle in the osteotomy of benign lesions of the mandible using a digital template. Br J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.bjoms.2015.04.013
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D. Huang et al. / British Journal of Oral and Maxillofacial Surgery xxx (2015) xxx–xxx
Table 2 Outcome of 6 patients. Case No.
Follow up (months)
1 9 2 12 8 3 5 4 8 5 6 5 Mean (SD) 7.8 (2.6)
Maximum mouth opening (mm)
Current perception threshold on the affected side (??)
Current perception threshold on the normal side (??)
Left mandibular angle Right mandibular angle point to midsagittal point to midsagittal plane (mm) plane (mm)
44 34 32 32 35 32 34.8 (4.7)
9.9 0 0 0 7.0 9.4 4.39 (4.90)*
8.45 0 0 0 6.0 7.0 3.58 (3.99)*
48.97 53.30 44.84 47.77 46.77 40.79 47.07 (4.18)**
46.13 50.25 43.42 50.16 45.95 43.92 46.64 (2.96)**
*p=0.56 and ** p=0.90. AQ: please add SD where indicated. A summary statistic (mean) should not be given without an indication of scatter (SD=standard deviation). Please do not use the word “average”, as it can refer to mean, median, or mode. Please state which units were used to measure current perception thresholds where indicated.
the inferior alveolar neurovascular bundles were protected in all patients, and nerve function recovered. The key points of this method were first that the boundaries of the lesion must be confirmed by CT on both axial and coronal sections, so that the osteotomy can be sufficient to prevent recurrence. Secondly, the 3-dimensional reconstruction of the inferior alveolar canal is the most important procedure. We found that some canals were not in their original anatomical position because of the pressure of the lesions, so they must be marked and segmented carefully. We found that coronal CT was the best imaging technique to identify the canal from the lesion, so we suggested that the reconstruction procedure should be done according to coronal CT data. Thirdly, the template should be designed just below the projection of the inferior alveolar canal on the surface of the bone, and its depth should be measured to help the surgeon to define exactly where it is during the operation. More and more surgeons have paid attention to the functions of nerves in recent years, (either by preserving or reconstructing them) so that they avoid postoperative numbness and improve the patients’ quality of life postoperatively.1–3,10 Kuriakose et al.,1 traced the inferior alveolar neurovascular bundle from the mental foramen on panoramic films. However, the nerve canal was always displaced as a result of pressure exerted by the lesion, so the nerve might be damaged because of inaccurate analysis based only on plain radiographs. Wittwer et al.,3 reported 3-dimensional reconstruction of the inferior alveolar canal, but because they lacked an effective way to locate the canal during operation unexpected nerve damage was possible. Bagheri et al.,10 studied the reconstruction of a damaged alveolar nerve, but the procedure was complicated, and the recovery of neurological function was unpredictable and unstable. Nerve function has often been evaluated using subjective descriptions or scales.1.3.9,10 Yoshimura et al.,11 reported resection of an ossifying mandibular fibroma, reconstruction with iliac bone, and simultaneous reconstruction of the inferior alveolar neurovascular bundle with a great auricular nerve graft. At 10-year follow up the patient had good aesthetics and function. They confirmed using Semmes-Weinstein monofilaments that the function of the nerve started to
improve gradually 3 months after operation. However, the measurements or scales were based mainly on the patient’s subjective feelings, which meant that the evaluation was not accurate enough. In contrast, we used the computer-assisted design technique for accurate protection of the neurovascular bundle, which has certain advantages. First, 3-dimensional reconstruction techniques were used to trace and analyse the path of the inferior alveolar canal, and to measure its depth, which helps the surgeon more than conventional plain radiographs or CT. Secondly, a special digital template was made to guide the procedure. The comparison of CT images before and after operation proved that the template can help the surgeon to make a precise osteotomy, so the neuromuscular bundle can be preserved. Thirdly, we used a mirror image of the unaffected side to help design the mandibular reconstruction. The titanium plate was then bent on a model preoperatively, which reduced the operating time appreciably.6 Postoperative CT showed good facial symmetry. Finally, the lesions affected the mandible in all cases, and in case numbers 1, 2, 3, 4, and 6 the temporomandibular joint was also involved. We therefore chose different approaches and methods to reconstruct the resected part of the mandible. The unaffected articular discs were preserved in all patients, which helped rapid recovery of function of the joints postoperatively.12,13 Follow-up showed a mean (SD) maximum mouth opening of 35 (4.7) mm and stable occlusions. The most important limitation of our method is that the digital template could provide only approximate information about the inferior alveolar canal, as it gave only a projection and not its exact position. However, we are looking forward to using the intraoperative navigation technique for the future treatment of benign lesions of the mandible. Conflict of Interest We have no conflict of interest. Ethics statement/confirmation of patient permission This study was approved by the ethics board of the hospital.
Please cite this article in press as: Huang D, et al. Preservation of the inferior alveolar neurovascular bundle in the osteotomy of benign lesions of the mandible using a digital template. Br J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.bjoms.2015.04.013
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Acknowledgements We would like to thank Engineer Sun Tao from Materialize Company for his great help in the designing procedures. References 1. Kuriakose MA, Lee JJ, DeLacure MD. Inferior alveolar nervepreserving mandibulectomy for nonmalignant lesions. Laryngoscope 2003;113:1269–73. 2. Degerliyurt K, Akar V, Denizci S, Yucel E. Bone lid technique with piezosurgery to preserve inferior alveolar nerve. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;108:e1–5. 3. Wittwer G, Adeyemo WL, Beinemann J, Juergens P. Evaluation of risk of injury to the inferior alveolar nerve with classical sagittal split osteotomy technique and proposed alternative surgical techniques using computerassisted surgery. Int J Oral Maxillofac Surg 2012;41:79–86. 4. Xia JJ, Gateno J, Teichgraeber JF. Three-dimensional computer-aided surgical simulation for maxillofacial surgery. Atlas Oral Maxillofac Surg Clin North Am 2005;13:25–39. 5. Shen Y, Sun J, Li J, Ji T, Li MM. A revised approach for mandibular reconstruction with the vascularized iliac crest flap by virtual surgical planning. J Plast Reconstr Surg 2012;129:e565–6. 6. Zhang S, Liu X, Xu Y, et al. Application of rapid prototyping for temporomandibular joint reconstruction. J Oral Maxillofac Surg 2011;69:432–8.
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7. He DM, Huang D, Yang C, Gou H. Application of computerassisted design and manufacture technique in the treatment of condylar osteochondroma combined with jaw bone deformities: Report of a case. Journal of Oral and Maxillofacial Surgery Medicine and Pathology 2013;25:46–51. 8. Sharaf B, Levine JP, Hirsch DL, Bastidas JA, Schiff BA, Garfein ES. Importance of computer-aided design and manufacturing technology in the multidisciplinary approach to head and neck reconstruction. J Craniofac Surg 2010;21:1277–80. 9. He DM, Yang C, Chen MJ, Bin J, Zhang X, Qiu Y. Modified preauricular approach and rigid internal fixation for intracapsular condyle fracture of the mandible. J Oral Maxillofac Surg 2010;68:1578–84. 10. Bagheri SC, Meyer RA, Cho SH, Thoppay J, Khan HA, Steed MB. Microsurgical repair of the inferior alveolar nerve: success rate and factors that adversely affect outcome. J Oral Maxillofac Surg 2012;70:1978–90. 11. Yoshimura H, Ohba S, Nakamura M, Sano K. Mandibular reconstruction using iliac bone and great auricular nerve grafts and oral rehabilitation using osseointegrated implants in a patient with a large ossifying fibroma: a 10-year follow up study. J Oral Maxillofac Surg 2013;71: 2176–88. 12. Chen MJ, Yang C, Fang B, Zhang S, Xu K. Treatment of hemimandibular fibrous dysplasia with radical excision and immediate reconstruction with free double costochondral graft. J Oral Maxillofac Surg 2010;68: 2000–4. 13. Qiu YT, Yang C, Chen MJ. Endoscopically assisted reconstruction of the mandibular condyle with a costochondral graft through a modified preauricular approach. Br J Oral Maxillofac Surg 2010;48:443–7.
Please cite this article in press as: Huang D, et al. Preservation of the inferior alveolar neurovascular bundle in the osteotomy of benign lesions of the mandible using a digital template. Br J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.bjoms.2015.04.013
ARTICLE IN PRESS Available online at www.sciencedirect.com
British Journal of Oral and Maxillofacial Surgery xxx (2015) xxx–xxx
Preservation of the inferior alveolar neurovascular bundle in the osteotomy of benign lesions of the mandible using a digital template夽 Dong Huang a,1 , MinJie Chen a,1 , DongMei He a,∗ , Chi Yang a,∗∗ , JianBing Yuan b , Guo Bai b , YiWen Wang a , WenBin Wei a , ZhuoZhi Chen a a
Department of Oral Surgery, Shanghai Ninth People’s Hospital, College of Stomatology, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai, China b School of Mechanical and Power Engineering, Shanghai Jiao Tong University. Shanghai, China Accepted 13 April 2015
Abstract Our aim was to evaluate the effect of a digital template in the preservation of the inferior alveolar neurovascular bundle during osteotomy for benign lesions of the mandible in 6 patients who were treated with mandibular osteotomies during 2013. Computed tomographic (CT) data were imported into ProPlan CMF 1.4 software. The borders of the lesion and the inferior alveolar canal were marked, and a digital template designed to mark the borders, outline the canal, and guide the osteotomy. A mirror image of the unaffected mandible was used to make a stereolithographic model by a rapid prototyping technique to prefabricate the reconstruction plate for the bone graft. The accuracy of the designs and the templates was evaluated during operation and postoperatively by CT. The sensation of the skin was tested using a Neurometer® CPT (current perception threshold) sensory detector (Neurotron Inc, Baltimore USA) to evaluate the function of the preserved inferior alveolar neurovascular bundle during follow up. With the digital template it was possible to guide removal of the bony lesion while accurately protecting the neurovascular bundle. Follow up for a mean of 8 months (range 5 -12) showed good facial symmetry, a stable occlusion, and recovery of sensation in the lower lip on the affected side. We conclude that a digital template can successfully help the resection of benign lesions of the mandible while preserving the function of the inferior alveolar neurovascular bundle. © 2015 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Keywords: Digital template; Inferior alveolar neurovascular bundle; Mandibular Benign Lesions; Mandible reconstruction
夽 This research was supported by Research Fund of Science and Technology Commission of Shanghai Municipality (08DZ2271100, 13XD1402300) and Research Fund of Biomedicine Engineering of Shanghai JiaoTong University (YG2009MS42). ∗ Corresponding author at: Department of Oral Surgery, Shanghai Ninth People’s Hospital, College of stomatology, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology. No. 639, Zhi Zao Ju Road, Shanghai, China. Tel.: +86 21 3271699 5707. ∗∗ Corresponding author at: Department of Oral Surgery, Shanghai Ninth People’s Hospital, College of stomatology, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology. No. 639, Zhi Zao Ju Road, Shanghai, China. Tel: +86 21 3271699 5218. E-mail addresses: [email protected] (D. He),[email protected] (C. Yang). 1 Authors D.H and M.C contributed equally to this work.
http://dx.doi.org/10.1016/j.bjoms.2015.04.013 0266-4356/© 2015 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Huang D, et al. Preservation of the inferior alveolar neurovascular bundle in the osteotomy of benign lesions of the mandible using a digital template. Br J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.bjoms.2015.04.013
YBJOM-4503; No. of Pages 5
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ARTICLE IN PRESS D. Huang et al. / British Journal of Oral and Maxillofacial Surgery xxx (2015) xxx–xxx
Introduction
Table 1 Details of the patients.
Ossifying fibroma, osteomyelitis, and fibrous dysplasia are examples of common benign lesions in the mandible. They can present with swelling, facial asymmetry, and in some patients, infection.1–3 The most common treatments are curettage, mandibular contouring and, in severe cases, partial mandibulectomy with reconstruction may be necessary. However, the inferior alveolar neurovascular bundle, which controls the sensation of the skin of the lower lip and chin, may be jeopardised during operation and this can result in postoperative numbness of the lower lip and chin.1–3 Some authors have reported successful preservation of the neurovascular bundle, which improved patients’ quality of life after operation.1–3 However, the disadvantages of these studies were that they used only conventional plain radiographs or computed tomographic (CT) images to trace the path of the inferior alveolar canal preoperatively, and did not describe an effective way to transfer the osteotomy plan and design into a live procedure, so precision was not possible. In recent years, computer-aided surgical techniques have been more widely used in oral and maxillofacial surgery, including 3-dimensional cephalometry, surgical design and simulation, CAD/CAM digital osteotomy templates, intraoperative navigation, and postoperative evaluation.4 Some authors have reported the use of computer-aided techniques in the treatment of mandibular benign lesions including for design of the osteotomy plane and production of digital osteotomy templates, and design and production of templates for remodelling and grafting bone.5,6 The intraoperative use of all types of templates can greatly improve the accuracy of resection and reconstruction, reduce operating time and the degree of trauma, and improve postoperative facial symmetry and aesthetics.5–8 However, to our knowledge the preservation of the inferior alveolar neurovascular bundle with the help of digital template has not been reported so far. We describe here how we fabricated a digital template by computer-assisted techniques to help us mark the borders of the lesion and outline the inferior alveolar canal during osteotomy to preserve the neurovascular bundle and to maintain its sensory function. We evaluated the accuracy of the technique and the template during and after operation on CT images, and the nerve function during follow up with a Neurometer® CPT (current perception threshold) sensory detector (Neurotron Inc, Baltimore, USA).
Case No
Sex
Age (years)
Affected side
Diagnosis
1 2 3 4 5 6
Male Male Female Female Female Female
18 28 20 37 18 44
Right Left Left Right Left Right
Ossifying fibroma Fibrous dysplasia Fibrous dysplasia Ossifying fibroma Osteomyelitis Osteomyelitis
All patients except case 5 had a costochondral graft through preauricular and submandibular approaches. Case 5 had an iliac bone graft through preauricular and intraoral approaches.
mandible, but in each case the inferior alveolar canal was unaffected compared with the opposite side. Plan of treatment and fabrication of the digital template Three-dimensional reconstruction of the inferior alveolar canal: data from a thin-layer CT scan (0.625 mm) were imported into ProPlan CMF 1.4 software (Materialize, Leuven, Belgium) in DICOM format, followed by 3-dimensional reconstruction and segmentation of the maxilla and mandible. The inferior alveolar canal was traced and marked from the mental foramen to the mandibular uvula in coronal layers, and then the 3-dimensional image of the canal was reconstructed (Fig. 1). Design of the osteotomy and template to preserve the nerve: the mandible was shown as transparent to show the inferior alveolar canal. The osteotomy planes were designed within the normal bone, just below the projection of the canal on the surface of the bone. Segments of bone were resected and the canal preserved. Marks were made on the osteotomy plane to show the measured depth of the canal, which guided the intraoperative separation of the inferior alveolar neurovascular bundle (Fig. 1). A digital template for the osteotomy with preservation of the nerve was then designed, with the upper edge indicating the osteotomy plane and the border of the lesion, and the lower edge surrounding the mandibular
Patients and Methods Patients with benign mandibular lesions that were treated by mandibular osteotomy and bone grafting for reconstruction during 2013 were included in the study (Table 1). On clinical examination all patients had facial asymmetry, together with obvious swelling of the mandible on the affected side but no numbness of the chin and lip. CT showed considerable swelling and bony changes in the affected
Fig. 1. Three-dimensional reconstruction of the inferior alveolar canal and design of the osteotomy plane. The numbers indicate the depth of the inferior alveolar canal at each marked point (mm).
Please cite this article in press as: Huang D, et al. Preservation of the inferior alveolar neurovascular bundle in the osteotomy of benign lesions of the mandible using a digital template. Br J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.bjoms.2015.04.013
YBJOM-4503; No. of Pages 5
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Fig. 3. Separation and protection of the inferior alveolar neurovascular bundle (yellow arrow).
plates in accordance with the model of the mirror image after intermaxillary fixation. Evaluation of outcome postoperatively
Fig. 2. A = design of the digital template according to computed tomographic data and the osteotomy design. B= use of the digital template during the operation.
Postoperative CT data were imported into the software, and facial symmetry evaluated by measuring the distance from the mandibular angle point to the middle sagittal plane. During follow up the Neurometer® CPT (current perception threshold) sensory detector was used to evaluate the sensation of the skin of the chin and the lower lip, and the difference between the two sides was calculated to assess the function of the inferior alveolar neurovascular bundle.
body and ramus (Fig. 2A). A mirror image was taken of the unaffected mandible in the midsagittal plane, and a model made using a rapid prototyping technique to prefabricate the titanium reconstruction plate. Fabrication of the digital template: the design of the osteotomy templates was exported as stereolithographic files, which were then imported into a rapid prototyping machine to manufacture the digital templates (Shanghai JiaoTong University School of Mechanical and Power Engineering). The templates were then sterilised with plasma for surgical use.
Statistical analysis
Intraoperative use of the digital templates
Six patients were included in this study (Table 1). Details of the operations and follow up are shown in Table 2. The digital templates fitted well on the mandibular surface, and no nerve damage was found during surgery. Postoperative CT showed that the mandibular lesions had been removed completely. Distances from the mandibular angle point to the midsagittal plane on the reconstructed side did not differ significantly from those on the unaffected side (p = 0.90) (Table 2).
All patients had their lesions resected under general anaesthesia followed by mandibular reconstruction by either costochondral graft or iliac bone graft through a modified preauricular 9 and submandibular approach (except case 5 when we used an intraoral approach) (Table 1). Mandibular osteotomies were made according to the digital template to mark the borders of the lesion. A careful cut was made along the upper border of the template, indicating the trajectory of the inferior alveolar canal, according to the depth measured preoperatively from the buccal bone surface to the canal itself (Fig. 2B). The neurovascular bundle was then separated and protected (Fig. 3). Bone grafts were harvested to reconstruct the resected mandible and fixed by the prefabricated
The Go-MSP distances on both sides and values for current perception thresholds during follow up were assessed using a paired t test, and probabilities of less than 0.05 were accepted as significant. For all statistical analyses we use SPSS 17.0 (version 17, SPSS Inc, Chicago, USA) software.
Results
Discussion Because we created patient-specific templates to protect the nerve during operations for benign lesions of the mandible,
Please cite this article in press as: Huang D, et al. Preservation of the inferior alveolar neurovascular bundle in the osteotomy of benign lesions of the mandible using a digital template. Br J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.bjoms.2015.04.013
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Table 2 Outcome of 6 patients. Case No.
Follow up (months)
1 9 2 12 8 3 5 4 8 5 6 5 Mean (SD) 7.8 (2.6)
Maximum mouth opening (mm)
Current perception threshold on the affected side (??)
Current perception threshold on the normal side (??)
Left mandibular angle Right mandibular angle point to midsagittal point to midsagittal plane (mm) plane (mm)
44 34 32 32 35 32 34.8 (4.7)
9.9 0 0 0 7.0 9.4 4.39 (4.90)*
8.45 0 0 0 6.0 7.0 3.58 (3.99)*
48.97 53.30 44.84 47.77 46.77 40.79 47.07 (4.18)**
46.13 50.25 43.42 50.16 45.95 43.92 46.64 (2.96)**
*p=0.56 and ** p=0.90. AQ: please add SD where indicated. A summary statistic (mean) should not be given without an indication of scatter (SD=standard deviation). Please do not use the word “average”, as it can refer to mean, median, or mode. Please state which units were used to measure current perception thresholds where indicated.
the inferior alveolar neurovascular bundles were protected in all patients, and nerve function recovered. The key points of this method were first that the boundaries of the lesion must be confirmed by CT on both axial and coronal sections, so that the osteotomy can be sufficient to prevent recurrence. Secondly, the 3-dimensional reconstruction of the inferior alveolar canal is the most important procedure. We found that some canals were not in their original anatomical position because of the pressure of the lesions, so they must be marked and segmented carefully. We found that coronal CT was the best imaging technique to identify the canal from the lesion, so we suggested that the reconstruction procedure should be done according to coronal CT data. Thirdly, the template should be designed just below the projection of the inferior alveolar canal on the surface of the bone, and its depth should be measured to help the surgeon to define exactly where it is during the operation. More and more surgeons have paid attention to the functions of nerves in recent years, (either by preserving or reconstructing them) so that they avoid postoperative numbness and improve the patients’ quality of life postoperatively.1–3,10 Kuriakose et al.,1 traced the inferior alveolar neurovascular bundle from the mental foramen on panoramic films. However, the nerve canal was always displaced as a result of pressure exerted by the lesion, so the nerve might be damaged because of inaccurate analysis based only on plain radiographs. Wittwer et al.,3 reported 3-dimensional reconstruction of the inferior alveolar canal, but because they lacked an effective way to locate the canal during operation unexpected nerve damage was possible. Bagheri et al.,10 studied the reconstruction of a damaged alveolar nerve, but the procedure was complicated, and the recovery of neurological function was unpredictable and unstable. Nerve function has often been evaluated using subjective descriptions or scales.1.3.9,10 Yoshimura et al.,11 reported resection of an ossifying mandibular fibroma, reconstruction with iliac bone, and simultaneous reconstruction of the inferior alveolar neurovascular bundle with a great auricular nerve graft. At 10-year follow up the patient had good aesthetics and function. They confirmed using Semmes-Weinstein monofilaments that the function of the nerve started to
improve gradually 3 months after operation. However, the measurements or scales were based mainly on the patient’s subjective feelings, which meant that the evaluation was not accurate enough. In contrast, we used the computer-assisted design technique for accurate protection of the neurovascular bundle, which has certain advantages. First, 3-dimensional reconstruction techniques were used to trace and analyse the path of the inferior alveolar canal, and to measure its depth, which helps the surgeon more than conventional plain radiographs or CT. Secondly, a special digital template was made to guide the procedure. The comparison of CT images before and after operation proved that the template can help the surgeon to make a precise osteotomy, so the neuromuscular bundle can be preserved. Thirdly, we used a mirror image of the unaffected side to help design the mandibular reconstruction. The titanium plate was then bent on a model preoperatively, which reduced the operating time appreciably.6 Postoperative CT showed good facial symmetry. Finally, the lesions affected the mandible in all cases, and in case numbers 1, 2, 3, 4, and 6 the temporomandibular joint was also involved. We therefore chose different approaches and methods to reconstruct the resected part of the mandible. The unaffected articular discs were preserved in all patients, which helped rapid recovery of function of the joints postoperatively.12,13 Follow-up showed a mean (SD) maximum mouth opening of 35 (4.7) mm and stable occlusions. The most important limitation of our method is that the digital template could provide only approximate information about the inferior alveolar canal, as it gave only a projection and not its exact position. However, we are looking forward to using the intraoperative navigation technique for the future treatment of benign lesions of the mandible. Conflict of Interest We have no conflict of interest. Ethics statement/confirmation of patient permission This study was approved by the ethics board of the hospital.
Please cite this article in press as: Huang D, et al. Preservation of the inferior alveolar neurovascular bundle in the osteotomy of benign lesions of the mandible using a digital template. Br J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.bjoms.2015.04.013
YBJOM-4503; No. of Pages 5
ARTICLE IN PRESS D. Huang et al. / British Journal of Oral and Maxillofacial Surgery xxx (2015) xxx–xxx
Acknowledgements We would like to thank Engineer Sun Tao from Materialize Company for his great help in the designing procedures. References 1. Kuriakose MA, Lee JJ, DeLacure MD. Inferior alveolar nervepreserving mandibulectomy for nonmalignant lesions. Laryngoscope 2003;113:1269–73. 2. Degerliyurt K, Akar V, Denizci S, Yucel E. Bone lid technique with piezosurgery to preserve inferior alveolar nerve. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;108:e1–5. 3. Wittwer G, Adeyemo WL, Beinemann J, Juergens P. Evaluation of risk of injury to the inferior alveolar nerve with classical sagittal split osteotomy technique and proposed alternative surgical techniques using computerassisted surgery. Int J Oral Maxillofac Surg 2012;41:79–86. 4. Xia JJ, Gateno J, Teichgraeber JF. Three-dimensional computer-aided surgical simulation for maxillofacial surgery. Atlas Oral Maxillofac Surg Clin North Am 2005;13:25–39. 5. Shen Y, Sun J, Li J, Ji T, Li MM. A revised approach for mandibular reconstruction with the vascularized iliac crest flap by virtual surgical planning. J Plast Reconstr Surg 2012;129:e565–6. 6. Zhang S, Liu X, Xu Y, et al. Application of rapid prototyping for temporomandibular joint reconstruction. J Oral Maxillofac Surg 2011;69:432–8.
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7. He DM, Huang D, Yang C, Gou H. Application of computerassisted design and manufacture technique in the treatment of condylar osteochondroma combined with jaw bone deformities: Report of a case. Journal of Oral and Maxillofacial Surgery Medicine and Pathology 2013;25:46–51. 8. Sharaf B, Levine JP, Hirsch DL, Bastidas JA, Schiff BA, Garfein ES. Importance of computer-aided design and manufacturing technology in the multidisciplinary approach to head and neck reconstruction. J Craniofac Surg 2010;21:1277–80. 9. He DM, Yang C, Chen MJ, Bin J, Zhang X, Qiu Y. Modified preauricular approach and rigid internal fixation for intracapsular condyle fracture of the mandible. J Oral Maxillofac Surg 2010;68:1578–84. 10. Bagheri SC, Meyer RA, Cho SH, Thoppay J, Khan HA, Steed MB. Microsurgical repair of the inferior alveolar nerve: success rate and factors that adversely affect outcome. J Oral Maxillofac Surg 2012;70:1978–90. 11. Yoshimura H, Ohba S, Nakamura M, Sano K. Mandibular reconstruction using iliac bone and great auricular nerve grafts and oral rehabilitation using osseointegrated implants in a patient with a large ossifying fibroma: a 10-year follow up study. J Oral Maxillofac Surg 2013;71: 2176–88. 12. Chen MJ, Yang C, Fang B, Zhang S, Xu K. Treatment of hemimandibular fibrous dysplasia with radical excision and immediate reconstruction with free double costochondral graft. J Oral Maxillofac Surg 2010;68: 2000–4. 13. Qiu YT, Yang C, Chen MJ. Endoscopically assisted reconstruction of the mandibular condyle with a costochondral graft through a modified preauricular approach. Br J Oral Maxillofac Surg 2010;48:443–7.
Please cite this article in press as: Huang D, et al. Preservation of the inferior alveolar neurovascular bundle in the osteotomy of benign lesions of the mandible using a digital template. Br J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.bjoms.2015.04.013