ENT E-Update masthead
MUSC Otolaryngology - Head & Neck Surgery E-Update                 March 2016 
  Greetings Colleagues,

This month's MUSC ENT E-Update is again authored by one of our newest faculty members, Andrew T. Huang, M.D., of our Head & Neck Oncology Division.
These newsletters are designed to provide brief, practical, clinical updates in areas where we all struggle in managing our patients. Your feedback or questions about the E-Update articles, your patients, or any other ENT issue are always welcome. Write to us at entupdate@musc.edu - And please forward this E-Update to your colleagues who may also benefit from sharing the latest ENT topics. As always, your support is deeply appreciated.

Yours sincerely,
Paul R. Lambert, M.D.
Professor and Department Chair

Computer-aided Design and Manufacturing
in Head and Neck Reconstruction:
from Virtual Reality to Reality

Andrew T. Huang, M.D.

Reconstruction of segmental bony defects of the maxilla and mandible following traumatic injury or oncologic resection has been revolutionized by the introduction of microvascular free tissue transfer.  Specifically, since its first description by Hidalgo et al1, the osteocutaneous fibula free flap (OFFF) in reconstruction of maxillary and mandibular deficits has been demonstrated to result in superior functional and aesthetic outcomes compared to pedicled flap and prosthetic reconstructions2,3.  The OFFF is ideal as a donor site for these reconstructions due to its provision of an ample length of thick bicortical bone, well-vascularized fasciocutaneous tissue for intraoral resurfacing, and the ability to harvest muscular tissue from the flexor hallucis longus or soleus for more extensive cavitary defects.
Figure 1. Preoperative planning of a total palatectomy defect secondary to osteonecrosis and osteomyelitis. A. 3-D model of the total palatectomy defect. B. Frontal view of the patient pre-operatively. Note loss of upper lip projection. C. Intraoperative view of the total palatectomy deformity (NS=nasal septum, IT=inferior turbinate, MS=maxillary sinus).
As OFFF reconstruction for complex defects of the maxilla and mandible becomes standard practice, limitations and pitfalls in its use have been encountered.  Standard OFFF procedures involve intraoperative conformation of titanium reconstruction plates to the native mandible or maxilla prior to resection in order to construct patient-specific anatomic templates for freehand shaping of the fibula. No matter the skill of the surgeon, this intraoperative freehand technique can result in shaping inaccuracies that not only translate to increased operative time needed for correction of these errors, but can also ultimately lead to poor bony apposition, malunion, fracture, and negative cosmetic appearance.  In addition, in cases of large tumors or trauma that distort or destroy a patient's normal bony anatomy, the ability to construct intraoperative templates that accurately restore native anatomic relationships can be difficult to impossible.
Figure 2. CAD/CAM plan and intraoperative technique. A. Virtual cutting guide on the left fibula bone.  Slots allow easy placement of an oscillating saw to create precise shaping osteotomies. B. Virtual model showing the shaped fibula in place. C. Left leg donor site marked for flap harvest. D. OFFF harvested, contoured, and ready for inset. E. Microvascular anatomosis between the peroneal and facial vessels (A=Artery, V=Vein). F. OFFF inset with skin paddle exposed for monitoring.
To remedy these issues, new surgical protocols involving computer-aided design and computer-aided manufacturing (CAD/CAM) for OFFF reconstruction have been devised and are now available commercially.  This technique utilizes high-resolution computed tomography (CT) scan imaging of both the surgical resection site and fibula donor site to pre-operatively plan and develop patient-specific models, cutting guides, and reconstruction plates used in OFFF reconstruction.  CAD/CAM protocols consist of three stages: 1.) Virtual surgical planning (VSP); 2.) Rapid manufacture of the customized surgical devices; and 3.) The surgery itself.   VSP requires the cooperation of the ablative surgeon, reconstructive microsurgeon, and a biomedical engineer to precisely map and detail the extent of surgical resection based on CT imaging which, in turn, allows the planning and development of specific fibular cutting guides and reconstruction plates used to exactly contour a straight fibula bone into a 3-D neomandible or neomaxilla.  In cases where there is loss of native bony anatomical references needed for planning a reconstruction, a major benefit of VSP is the ability to develop fibular constructs that mirror contralateral bony landmarks, or, when all reference points are absent, develop constructs that adhere to ideal facial measurements and geometry.  Rapid manufacture of the customized models and guides can take eight business days, and although this may seem negative, it should be noted that the reconstruction plates created are milled, bent, heat-treated, and can be specifically engineered with increased individual bar widths, ultimately conferring an up to 40% improved fatigue strength compared to standard reconstruction bars 4.  Surgical harvest of the OFFF is unchanged compared to standard techniques.  Once harvested, however, utilization of the customized cutting guides allows precise shaping of osteotomies and expedient bony inset which has been demonstrated to significantly decrease flap ischemia operative time 5,6.
Figure 3. 6 week post-operative result. A. Left lateral view. B. Right lateral view. C. Frontal view. D. Intraoral view of skin paddle healed in place.
Indications for CAD/CAM use are not universal yet, but at our institution it is reserved for complex bony reconstructions of the head and neck where normal anatomic landmarks are abnormal or absent, and in cases where extended length of fibula bone is required, necessitating minimization of error and discarded bone during shaping.  Pre-operatively planning complex surgical defects of the maxilla and mandible allows the surgeon, with the integral assistance of a biomedical engineer, to develop patient-specific reconstructive plans, maximizing both functional and aesthetic outcomes while minimizing flap ischemia operative time.  Although not yet proven, the utilization of stronger, milled reconstruction plates may reduce post-operative plate fracture, reducing re-operation rates.
  1. Hidalgo DA. Fibula free flap: a new method of mandible reconstruction. Plast Reconstr Surg.  1989;84:71-79.
  2. Urken ML, Buchbinder D, Weinberg H, et al. Functional evaluation following microvascular oromandibular reconstruction of the oral cancer patient: a comparative study of reconstructed and nonreconstructed patients. Laryngoscope. 1991;101:935-950.
  3. Talesnik A, Markowitz B, Calcaterra T, Ahn C, Shaw W. Cost and outcome of osteocutaneous free-tissue transfer versus pedicled soft-tissue reconstruction for composite mandibular defects.  Plast Reconstr Surg. 1996;97:1167-1178.
  4. Dynamic Testing. Reports available at Stryker Leibinger GmbH & Co. KG.
  5. Gangopadhyay N, Villa MT, Chang EI, Selber JC, Liu J, Garvey PB. Combining preoperative CTA mapping of the peroneal artery and its perforators with virtual planning for free fibula flap reconstruction of mandibulectomy defects.  Plast Reconstr Surg.  2015;136(4 Suppl):8-9.
  6. Rustemeyer J, Sari-Rieger A, Melenberg A, Busch A. Comparison of intraoperative time measurements between osseus reconstructions with free fibula flaps applying computer-aided designed/computer-aided manufactured and conventional techniques. Oral Maxillofac Surg. 2015;19:293-300.
Dr. Andrew T. Huang
Andrew T. Huang, M.D.

Assistant Professor, ENT

M.D.: University of Miami
Residency: Virginia Commonwealth University Health System
Fellowship: M.D. Anderson Cancer Center
Special Interests: Head and neck oncology, microvascular reconstruction
Email: huanga@musc.edu

E-Update Articles 
Look for these articles in upcoming issues!

April: Novel Metrics to Evaluate Image-Guided Cochlear Implant Programming Outcomes
May: Dynamic re-animation options for facial paralysis

June: Is Meniere's Disease a Migraine of the Inner Ear?

To view any of our past E-Updates visit our
Continuing Education
Southern States Rhinology Course
April 20 - 23, 2016

The Charleston Course: 6th Annual Otolaryngology Literature Update
August 5 - 7, 2016

31st Annual F. Johnson Putney Lectureship in Head & Neck Cancer 
MUSC Otolaryngology-Head & Neck Surgery | WEBSITE | EMAIL