Virtual Surgical Planning and 3D-Printed Surgical Guides in Facial Allotransplantation

Abstract

The complex three-dimensional (3D) anatomy in facial allotransplantation creates a unique challenge for surgical reconstruction. Evolution of virtual surgical planning (VSP) through computer-aided design and computer-aided manufacturing has advanced reconstructive outcomes for many craniomaxillofacial indications. Surgeons use VSP, 3D models, and surgical guides to analyze and to trial surgical approaches even prior to entering the operating room. This workflow allows the surgeon to plan osteotomies and to anticipate challenges, which improves surgical precision and accuracy, optimizes outcomes, and should reduce operating room time. We present the development, evolution, and utilization of VSP and 3D-printed guides in facial allotransplantation at our institution, from guide conception to first clinical case.

Facial vascularized composite tissue allotransplantation (VCA) is an evolving frontier in reconstructive microsurgery for complex and devastating facial injuries when conventional reconstructions would otherwise yield suboptimal results. ¹ Face transplant recipients often have complex and challenging craniofacial anatomy due to the extensive defect and prior reconstruction attempts. Face transplant recipients may have significant disfigurement due to mechanisms such as high energy ballistic injury, electrical, thermal, or chemical burns, animal attacks, or surgical resection of large tumors, resulting in significant composite tissue loss. Reconstructions pose unique surgical challenges due to the three-dimensional (3D) configuration of specialized facial structures including the eyelids, nose, lips, and underlying skeletal structures. Defects vary significantly and therefore surgical planning requires a highly individualized approach to optimize form and function. Virtual surgical planning (VSP) with the creation of 3D guides is particularly helpful in complex craniomaxillofacial reconstructions. ^{2 3 4 5}

Inclusion of parts of the facial skeleton within facial allografts presents additional complexity to the technical aspects of harvest and inset. Our institution performed its first face transplantation in June 2016. The recipient patient was a 31-year-old male who sustained a self-inflicted gunshot injury when he was 21 years old that resulted in a several central facial injury ( Fig. 1 ). He underwent multiple reconstructive procedures including a free fibula osteocutaneous flap for mandible, a free iliac flap for maxilla, and multiple other open reduction and internal fixation procedures in the face. Given the extent of the defect, these conventional reconstructive techniques did not restore adequate form or function.

Fig. 1.

Preoperative ( A – C ) and postoperative ( D – F ) anteroposterior (AP) view in repose, lateral view, and AP view with smile of a patient with facial deformity reconstructed with a facial transplant. Postoperative images are from 4 years posttransplant. Copyright Mayo Clinic. All Rights Reserved.

To prepare for our first facial allotransplantation at Mayo Clinic, multiple cadaveric simulation dissections were used to refine our guides beginning in 2012. These included a series of over 50 Saturdays dedicated to anatomic dissections in the cadaver laboratory to mock face transplants performed using fresh recipient and donor cadaver heads. We performed these rehearsal sessions with biomedical surgical engineers from 3D Systems who collaborated closely to develop and improve these guides. Multiple iterations and refinements of our surgical guides led to the successful utilization of VSP and 3D-printed guide utilization in our institution's first face transplant in 2016.

In this article, we review the evolution of 3D-printed surgical guides in facial allotransplantation, discuss the role of VSP, computer-aided design (CAD), and computer-aided manufacturing (CAM) technologies in 3D printing and guide development, and detail how our refinement of guides within cadaveric facial transplantation models translated to our first facial allotransplantation.

Virtual Surgical Planning and 3D-Printed Guides

VSP and 3D models and guides are helpful in preoperative planning for complex craniomaxillofacial reconstructions. Surgeons use models to visualize, analyze, and manipulate spatial relationships in multiple dimensions and to trial different surgical approaches such as determining placement of osteotomies, thereby anticipating challenges, increasing surgical accuracy, and reducing operative time.

A close relationship between the surgeon and the biomedical engineer is essential to yield successful results in VSP and 3D-printed surgical guides. These sessions are necessary to review the images, discuss the surgical plan, and complete the design of the prefabricated 3D-printed guides. Improvement in resolution and quality of data derived from computed tomography (CT) or magnetic resonance imaging have enhanced the virtual environment and creation of 3D models and guides for surgical planning and refinement. The data obtained from the CT is sent digitally to a medical modeling facility for CAD and CAM. The CT scans are then segmented to create, modify, analyze, and optimize the 3D virtual reconstruction model. The use of CAD/CAM enables medical engineers to handle the data from the CT scans for surgical planning. The digital data are processed by cleaning artifacts, image segmentation, and fusion. Image segmentation refines anatomic structures and details. Data such as anatomical distances, bone thickness, intracranial volumes, and orbital volumes, are processed and calculated to create vector-based graphics, which aided with the execution of deliberate surgical steps, including osteotomies and hardware fixation.

Surgical guides created with VSP have been used in multiple craniofacial reconstructive procedures, ^{2 3 4 5 6} including mandibular reconstruction with free fibula, ^{7 8 9 10 11} free iliac flaps, ¹² or lateral scapular border, ¹³ with accuracy that often exceeded that without the use of virtual planning. ¹⁴ In maxillary reconstruction, the use of prefabricated VSP-generated cutting guides and plates eases free fibular flap molding and placement, minimizes operating time, and improves clinical outcomes. ¹⁵ Many surgical guides used in computer-guided implantology are scientifically validated for clinical use due to their accuracy when compared with other interventions. ¹⁶

Types of Guides

The most frequently used positioning aides in craniomaxillofacial surgery are interocclusal splints, which help to align tooth-bearing bony segments and act as reference to anatomical landmarks.

Cutting guides allow for precise osteotomy cuts, denoting the angulation and beveling of the osteotomy plane with tilted slots. Guides can be fitted with depth stops or outrigger arms for protection of neurovascular structures. These guides must comply with the blade and drill characteristics (e.g., length, width), cutting guides allow for precise location, angulation, and beveling of the osteotomy plane with blade-guiding slots. The friction of the drill with the bone and the surgical guide may interfere with the accuracy of the guide. Custom-designed metal sleeves within the surgical guides specific to the blades for osteotomies may improve precision and accuracy. More recently, guides are created out of titanium with the blade-guiding slots printed as part of the guide.

Guides can also be fitted with depth stops for soft tissue or neurovascular protection. The design of guides must comply with the blade and drill bit (width, length, rigidity) characteristics of the power tool (e.g., piezoelectric, oscillating saw, etc.). Cutting guides must have sufficient contact surface and are complemented with collars that embrace the bony contours to ensure positioning. Cutting guides are often used in orthognathic procedures such as LeFort I osteotomy, bony resections in tumors, harvesting and contouring of bone flaps, and osteotomies for cranial vault remodeling.

Resection guides can also be used for segmental osteotomies, and can be designed as individual components or contiguously. Hyperostotic bone formations such as in fibrous dysplasia may require bony resections over extensive areas at a specific depth level and can be fashioned as such with depth stops.

Virtual Surgical Planning and 3D-Printed Guides in Facial Allotransplantation

Surgical guides are particularly helpful in facial allotransplantation, where small deviations can trigger a reaction of incongruencies and malalignment. VSP allows for anticipating osteotomies in a controlled environment in which the recipient defect and donor anatomy can be assessed, and the operative plan refined, which may translate into improved cephalometric and occlusal relationships and outcomes ( Fig. 2 ).

Fig. 2.

Design of facial flap including facial nerve branches ( top left ); surgical guides and planned osteotomies designed in collaboration with 3D Systems ( top right ); posterior view of flap design including bone and soft tissue ( bottom left ); illustration of planned final reconstruction ( bottom right ).

Accurate bony restoration is critical, since any size or shape mismatch between the donor and recipient can affect alignment and consolidation of the transplanted segments, thereby affecting functional outcomes including temporomandibular joint (TMJ) alignment and occlusion. VSP and 3D-printed guides can minimize donor-recipient size mismatches and enable optimal and predictable orthognathic alignment, potentially allowing for a larger pool of acceptable donors. Donor osteotomy guides enable cuts to take into consideration existing hardware and location of the pedicle. Furthermore, cutting guides and positioning guides are reciprocal, which results in more time efficient, streamlined, and unified intraoperative communication and decision-making between the donor and recipient surgical teams.

Herein, we describe the development of a virtual surgical plan and the evolution of our 3D-printed surgical guides in facial allotransplantation from cadaveric rehearsals in 2012 to operative execution in 2016. These included a series of over 50 sessions in the cadaver laboratory, 20 of which mock face transplants were performed using fresh recipient and donor cadaveric heads. These cadaveric rehearsal sessions were performed with biomedical surgical engineers from 3D Systems who collaborated closely for guide development and refinement, leading to successful utilization in our institution's first face transplant.

Importantly, the workflow developed here also enabled the logistics of accelerated turnaround and biomedical engineer communication to occur seamlessly in a high-pressure, complex case. We therefore highly recommend institutions initiating face transplant programs to incorporate similar sessions in their preparation to operationalize and streamline their workflow. Accuracy of these guides to preoperative surgical plan was confirmed through postoperative CT scanning of cadavers before moving forward with utilization of the guides in clinical cases.

Guide Design

We designed osteotomy donor and recipient guides based upon the virtual surgical plan ( Figs. 3 and 4 ). Donor guides were designed to be affixed more lateral to the transplanted facial segment so that hardware fixation and soft tissue stripping for guide fit did not compromise the allograft. Donor guides included: nasal osteotomy guide to the lower frontonasal bone and infraorbital rim; zygomatic-pterygoid guide fixed to the lateral zygomatic arch; mandibular sagittal split guide to the mandibular ramus and extending to the angle of the mandible, designed to avoid damage to the inferior alveolar nerve; and dental occlusal splint ( Fig. 5 ).

Fig. 3.

LeFort III and distal mandibular segment containing all the teeth from the donor and transplanted to the recipient. Yellow indicates bone transplanted and green indicates bone removed from the recipient to create the defect.

Fig. 4.

Computed tomography (CT) scan was used to create a three-dimensional (3D) virtual surgical plan for surgical guide design and osteotomy placement. Surgical guides were then printed and utilized in the face transplant cadaver laboratory sessions.

Fig. 5.

Computer-aided design and manufacturing (CAD-CAM) and virtual surgical planning (VSP) for osteotomies. For allografts including skeletal segments, VSP and CAD-CAM allows for patient-specific planning and execution of donor and recipient osteotomies with the aid of skeletal cutting guides. Donor osteotomy guides included a guide for nasal, zygoma, and pterygomaxillary cuts (upper left); a guide for the mandibular sagittal split (upper right and lower right); and a dental occlusion splint (lower left).

We created similar recipient midface guides to guide the nasal, pterygoid, and zygomatic osteotomies ( Fig. 6 ). A guide was affixed to each lateral zygomatic arch and mandibular angle to preserve the position of the jaw and TMJ. A small mandibular osteotomy guide was slid against a larger guide to guide position along the mandibular body. The final guide for the mandibular sagittal split osteotomy would allow for avoidance of damage to the inferior alveolar nerve. Following the sagittal split, the guides were replaced with positioning guides to preserve the position of the proximal mandible. Recipient guides were affixed to the donor allograft to ensure that screw fixation and soft tissue removal was on the segment to be removed to avoid compromising proximal tissue.

Fig. 6.

Recipient osteotomy guides included guides for zygoma, nasal, and pterygoid/maxillary cuts ( A ), and guides for the mandibular sagittal split osteotomy ( B ). A positional guide with screw holes that corresponded in the mandibular osteotomy guide was created to ensure the recipient temporomandibular joint was in the ideal position when the donor graft was plated ( C ).

A clear stereolithographic model of the planned donor tissue was used to assess areas of bony prominence on the recipient defect that would interfere with the planned fit of the donor face ( Fig. 7 ). The clear 3D-printed fit guide was created to allow the surgeon to visualize areas of interference and to burr areas of prominence as needed.

Fig. 7.

Three-dimensional (3D)-printed surgical fit guides on cadaveric model help to ensure the optimal fit of donor graft onto recipient. The guides are now printed clear to allow for recognition of bony prominences through the guide. ( A ) Anteroposterior view and ( B ) lateral view.

Donor Surgical Technique

Incisions were marked on the donor to include bilateral preauricular incisions, curved temple incisions, and subciliary incisions meeting at the nasal radix. Inferiorly, the incision was extended anteriorly through bilateral submandibular incisions extending to the submental area to meet in the midline. Subcutaneous flaps were dissected from the lateral incisions until 2 cm anterior to the parotid gland. A superficial parotidectomy was performed and the facial nerve branches were dissected anterograde until 3 cm anterior to the border of the parotid. This provided the best exposure of the nerve branches and reduced the bulk in the cheek following inset. The facial nerve trunk was then identified and dissected proximally to the stylomastoid foramen. This corresponded to the site for the final nerve anastomosis. The facial nerve was transected proximally at the foramen and dissected off the deeper structures past the anterior border of the masseter, and the nerve was reflected anteriorly with the skin flap. Desired sensory nerves were identified (infraorbital, inferior alveolar) and transected proximally to provide redundancy for coaptation with the recipient sensory nerves following bony inset. All necessary soft tissue to restore the recipient defect was included in the flap.

Following careful dissection, the osteotomy guides were then placed on the facial bones in the planned locations and secured in place. The masseter was removed to allow access to the mandible and place the cutting guides. The mandibular condyle and coronoid were removed through a transverse osteotomy below the sigmoid notch to allow access to the pterygomaxillary junction and to the inferior alveolar nerve, the lingual nerve, and the sensory nerve to the buccal mucosa.

We performed dissection of the nasofrontal region to allow placement of the guides. The insertion of both donor medial canthal tendons were left intact to provide anchors for the recipient medial canthal tendons. In coordination with the oculoplastic surgeon (E.B.), the lacrimal system was identified. The soft tissues over the zygomatic arch and orbital rim were stripped to fit the cutting guides. The facial artery and vein were dissected from adjacent tissues. Muscles of the floor of the mouth and strap muscles were detached from the mandible, preserving the periosteum and part of the tendinous attachments for a suture to the recipient's neck muscles to the donor mandible in the optimal location. The same dissection was then performed on the contralateral side of the face.

The VSP-designed osteotomy guides were used to increase precision of the cuts with the plan of which saw thickness was to be used. The guide was fixed to the zygoma and frontonasal bones utilizing titanium screws. LeFort III osteotomies were performed with the Piezoelectric System. Cutting guides were also designed with this blade. Osteotomies were performed on the nasal bones, lateral zygomatic arch, and pterygomaxillary junction, following the 3D-printed guides. Mandibular sagittal split guides were designed to avoid damage to the inferior alveolar nerve and osteotomies were performed. The inferior alveolar nerve was traced proximally in the donor and transected. The oral mucosa was incised. An osteotome was used to disimpact the LeFort III maxillomandibular complex. The donor segment was fitted against the reciprocal clear fit-assessment guide of the planned recipient defect and contoured as needed to achieve a perfect fit.

Recipient Surgical Technique

Recipient incisions were planned to take into consideration that the donor could become unstable during the procedure which might result in the procurement being aborted. Therefore, incisions were made in the nasolabial creases, eyelid cheek junction, and submandibular area. From the nasolabial crease, a thick subcutaneous flap was raised from medial to lateral, preserving preauricular perforators. This exposure also allowed dissection of the facial nerve branches anterior to the parotid gland to ensure adequate length for coaptation. Each branch was carefully identified and marked and photographs were taken. Following this, the neck was explored for recipient vessels (such as the facial or external carotid artery and the common facial vein). This dissection was also performed on the contralateral side.

The lacrimal system was dissected and preserved to be connected to the donor system. Soft tissues were stripped from the zygoma and nasal bones to enable optimal fitting of the osteotomy guides. The midface osteotomy guides were affixed to the zygoma and nasal bones utilizing screws and LeFort III osteotomies were performed. The Piezoelectric System was used. The midface osteotomy guides were then removed and the mandibular osteotomy guide was placed. The sagittal split osteotomy was performed with a guide. The inferior alveolar nerve was identified and cut distally. The mandibular osteotomy guide was removed and replaced with the mandibular positioning guide. The screw holes of the osteotomy guide corresponded with the positioning guide to ensure optimal position of the recipient proximal mandibular segment of the mandible and TMJ function. The oral mucosa was incised anteriorly. The recipient tissue was disimpacted and removed to complete creation of the planned recipient defect.

Recipient Facial Defect Reconstruction

The donor facial transplant was inset into the recipient defect and assessed for fit. The soft palate and oral mucosa was approximated and miniplates were prebent utilizing the 3D-printed models along the nasofrontal region, zygoma, frontozygomatic region, and mandible. Vascular anastomoses were performed, connecting the recipient facial artery to the donor facial artery, and the common facial vein of the recipient to the donor facial vein. Facial nerve anastomoses were performed to connect donor and recipient nerve branches as well as the inferior alveolar nerve and infraorbital nerves. Finally, all the soft tissue components were approximated and closed, including the intraoral soft tissue, suturing the donor to recipient palate, and buccal mucosa. The skin was tailored and closed.

Discussion

Optimizing workflow is critical for preoperative planning and for efficient execution of these complex procedures. Advances in VSP and 3D printing have enabled the assessment of challenging recipient anatomy. Simulations and cadaveric rehearsals allow the team to anticipate and troubleshoot potential challenges and to make refinements to the planned procedure such as surgical refinement through repetition and outcomes assessments. Our cadaveric simulations were invaluable to optimizing guide design and fit for our surgical plan, and further strengthened our collaboration and communication with surgical engineers and the entire surgical team. This relationship was particularly helpful when under the constraints and pressures of the actual surgical case. Specifically, these sessions improved the confidence of the entire team by enabling opportunities to optimize workflow including the logistics of printing and sterilizing guides.

3D-printed guides lead to many advantages in facial transplantation. This includes the reconstruction of donor-recipient size mismatches, which allows for a larger pool of acceptable donors. Guides assist in the planning of osteotomies to avoid previous hardware. Donor osteotomy guides enable accurate osteotomies to be performed with the vascular pedicle intact, unlike previous models that required the donor face to be modified under ischemia. Our guides also preserved the occlusion of the donor, and the clear fit-assessment guides were able to assess final fit prior to inset. Guides also allow for greater independence between the donor and recipient teams since cutting guides and clear fit-guides are reciprocal.

Manninen et al described their experience with 3D VSP in two bimaxillary face transplantations in Helsinki and analyzed the accuracy of virtual transplantation in predicting the result of facial transplantation. ¹⁷ CT scans of the recipient and donor were used to define the osteotomy sites and perform virtual transplantation and 3D print custom osteotomy guides for recipient and donor. Differences between cephalometric measurements of the virtually simulated and actual postoperative transplantation were calculated. They found no changes to the planned osteotomy lines were needed during surgery, and linear and angular measurements of virtual versus actual transplantations of the two patients varied between 0.1 to 5.6 mm and 0 to 4 degrees.

A 2021 systematic review assessed the accuracy of VSP in bimaxillary orthognathic surgery in bone by comparing mean linear and angular measurements of the VSP with the surgical result, and found excellent accuracy with virtual planning, despite lack of consensus on standardization to evaluate accuracy in virtual planning. ¹⁸ In this study, planning and printing errors related to the guide were less than 2 mm, and the averages of the errors related to virtual planning in the analysis of the different plans were less than 1 mm. In a 2022 systematic review of orthognathic surgeries, surgical guides were found to be highly precise and accurate, with low error values represented by the CAD/CAM technique. ¹⁹ VSP and 3D-printed guides have also been used as a volumetric assessment tool for soft tissue correction with fat grafting in facial asymmetry. ²⁰

While intraoperative navigation in facial allotransplantation can be useful in surgical accuracy, one disadvantage is the lack of precision of osteotomies compared with 3D-printed guides. However, as an adjunct, intraoperative surgical navigation allows for the ability to register and overlay the surgical plan onto the skeletal defect to assist with donor skeletal inset and fixation to the recipient. Within the dental implant literature, a 2019 systematic review and meta-analysis reported improved accuracy of computer-aided surgical template-aided implant placement compared with free hand operation, with no significant difference in survival rate. ²¹

In recent years, the use of VSP methods including mixed reality modalities has offered reconstructive teams instrumental help in terms of preoperative planning for face transplant. ²² Specifically, advances in 3D printing capabilities and the use of novel holographic craniofacial surgical planning applications may evolve new frontiers for virtual surgical practice. Holographic models in particular can be used to practice techniques in an unlimited fashion by multiple surgeons simultaneously and even have the potential to be used intraoperatively to provide intraoperative guidance. The utilization of holographic and mixed-reality has been one technique used in face transplant VSP and intraoperative osteotomy navigation. Intraoperative navigation systems have been another modality used to guide osteotomies based upon preoperative planning using CT imaging. This technique has been used in both mock face transplant cadaver studies and clinically. VSP and modeling has become routine for many indications including orthognathic surgery and facial allotransplantation over the past decade. ^{23 24 25 26 27 28}

Conclusion

VSP has advanced reconstructive outcomes in complex craniomaxillofacial surgery including facial allotransplantation. Matching the complex 3D anatomy of the donor and recipient craniofacial anatomy to optimize bony contact and occlusion can be a time-consuming process in the operating room. VSP allows for the ability to preoperatively visualize, manipulate, and troubleshoot 3D configurations of the craniomaxillofacial skeleton, thereby improving accuracy, precision, and reducing operative time. 3D-printed surgical guides improve communication between donor and recipient surgical teams and may improve aesthetic and functional outcomes. Guides improve surgical accuracy in facial VCA by planning for optimal osteotomy placement and alignment of transplanted tissue. Cadaveric rehearsal sessions can help to refine and optimize surgical guides by identifying barriers, troubleshooting issues, and facilitating seamless communication with the multidisciplinary team.