Bone reconstruction using CAD/CAM technology in head and neck surgical oncology. A narrative review of state of the art and aesthetic-functional outcomes| ACTA Otorhinolaryngologica Italica

Abstract

Bone defects following resections for head and neck tumours can cause significant func-tional and aesthetic defects. The choice of the optimal reconstructive method depends on several factors such as the size of the defect, location of the tumour, patient’s health and surgeon’s experience. The reconstructive gold standard is today represented by revascular-ised osteo-myocutaneous or osteomuscular flaps with osteosynthesis using titanium plates. Commonly used donor sites are the fibula, iliac crest, and lateral scapula/scapular angle. In recent years, computer-aided design (CAD)/computer assisted manufacturing (CAM) sys-tems have revolutionised the reconstructive field, with the introduction of stereolithograph-ic models, followed by virtual planning software and 3D printing of plates and prostheses. This technology has demonstrated excellent reliability in terms of accuracy, precision and predictability, leading to better operative outcomes, reduced surgical times and decreased complication rates. Among the disadvantages are high costs, implementation times and poor planning adaptability. These problems are finding a partial solution in the develop-ment of “in house” laboratories for planning and 3D printing. Strong indications for the use of CAD/CAM technologies today are the reconstruction of total or subtotal mandibular or maxillary defects and secondary bone reconstructions.

Introduction

Bony defects of the mandible and maxilla following oncological resection present particular challenges, as loss of the structural craniofacial framework has major implications for aesthetics and masticatory function, and miscalculations can result in suboptimal outcomes and/or poor quality of life.

Indeed, jaws are pivotal structures in the human craniofacial complex and their functions extend well beyond mere support and aesthetics. They are integral to various essential functions related to facial contour and aesthetics, upper airway patency, breathing, masticatory function, lip seal for swallowing and speech articulation.

The specific approach to jaw reconstruction after oncological resection depends on several factors, including the extent of tissue and bone loss, location of the tumour, the patient’s overall health, and surgeon’s expertise ^1-5.

Currently, osteo-myo-cutaneous or osteomuscular free tissue transfer with titanium plate fixation is the gold standard for maxillary and mandibular reconstruction ¹. Microvascular surgery allows the transfer of a large amount of bone and soft tissue with their own vascular supply to the head and neck, even in the face of contaminated wounds and previously irradiated recipient sites.

The commonly described donor sites are the fibula, iliac crest and lateral scapula/scapular tip. Although the fibula is still the major workhorse, the lateral scapula/scapular tip allows for complex soft tissue reconstruction from a single chimeric pedicle, and the iliac crest has the advantage of supplying bone with a height comparable to that of the native dentate mandible, thus improving oral competence by supporting the lower lip ^1,2.

The choice of donor site depends on several factors, including:

1. size and location of defects;
2. patient’s overall health and comorbidities;
3. surgeon’s expertise and familiarity with specific flaps;
4. necessity for immediate or delayed implant rehabilitation.

In recent years, reconstructive procedures have been revolutionised by technology. Conventional free-hand approaches have improved owing to the development of software for virtual planning (VP), computer-aided design/computer-assisted manufacturing (CAD/CAM) systems, and three-dimensional (3D) printing.

In this narrative literature review, the authors aim to discuss the current state-of-the-art application of CAD/CAM systems in reconstruction and rehabilitation of the jaws, to analyse the advantages and disadvantages, and preview potential future developments. These publications were summarised with the supplementation of papers yielded from keyword searches of each field using Google Scholar, PubMed, and ScienceDirect.

Stereolithographic models

One of the earliest applications of CAD/CAM systems in head and neck surgery was stereolithographic models. Computed tomography (CT) scans generate a series of cross-sectional images of the body, providing detailed information about structures within the head and neck. These images are uploaded into a specialised software that processes raw CT data and converts them into a three-dimensional digital model or code. This conversion involves segmenting images to differentiate various structures, such as bones, blood vessels, and soft tissues. The resulting digital code is then used in a stereolithographic 3D printer. The printer employs a process called stereolithography, which uses a laser to solidify layers of liquid resin, gradually building a 3D model based on the digital code obtained from CT scans. The availability of high-resolution CT scans (~1 mm slice thickness) allows for the creation of highly accurate and detailed physical replicas of the patient’s anatomy, particularly of facial bones (Fig. 1) and, when necessary, of the donor site ². The precision and detail of these 3D-printed models offer several advantages ^1-14:

1. preoperative planning: surgeons can closely examine the intricate structures of the head and neck, enabling them to strategise the surgery, anticipate challenges, and develop customised solutions for each patient;
2. plate pre-bending: the conventional task of free-hand bending the plates intraoperatively to fit both the defect and reconstructive flap can be time-consuming with limited accuracy, requiring frequent readjustments that can weaken titanium plates, especially with less experienced surgical teams ^1,2. Furthermore, inaccuracies in bony contouring may jeopardise the possibility of long-term osseointegration and increase the risk of plate exposure. The stereolithographic models allow for preoperative modelling of plates, leading to the improvement of reconstructive accuracy and an important reduction in operative and ischaemia times, plate manipulation and strength applied on it, risk of plate fracture, and bone malpositioning;
3. titanium mesh implant pre-bending in orbital reconstruction: the mesh can be shaped or pre-bent before surgery to match specific contours of the patient’s orbital anatomy. This customisation ensures a more precise fit during the reconstruction process and less trauma to orbital and peri-orbital tissues ^5,6;
4. education and communication: 3D models serve as valuable educational tools for both the surgical team and patient. Surgeons can explain the procedures more comprehensively, and patients can better visualise and understand the surgery proposed.

Computer-aided design (CAD) and virtual planning

A step beyond the use of stereolithographic models is now performed with the introduction of a virtual simulation software. This allows the conversion of bidimensional images obtained from high-resolution CT or MRI scans into 3D digital models. These models can be manipulated, segmented, and analysed by a surgical team to plan the procedure. Surgeons can use a virtual model to simulate the surgery, test different approaches, and plan the optimal path for the procedure. This simulation helps in identifying potential challenges and minimising risks. Virtual planning also allows for preoperative discussions and consultations among the surgical team, ensuring that everyone is on the same page regarding the surgical approach ².

A key point of this process is the preparation of a videoconference that usually takes place a few weeks prior to surgery, with the cooperation of a commercial supplier. The main professional figures involved are the ablative and reconstructive surgeons and the commercial engineering team. Starting from a 3D virtual model, digital rehearsal of the resection and reconstruction is performed.

Three-plane (coronal, axial, sagittal) osteotomies are designed for both the ablative segment and flap donor site, with the goal of achieving optimal reconstructive geometry, bone-to-bone contact, and preservation of blood supply to the soft tissue portions of the flap ^2-6.

The virtual is made real through 3D printing of anatomic models of the native anatomy and the reconstructive plan, which can guide plate modeling and in carrying out the procedure. A noticeable increase in accuracy is achieved through the printing of cutting guides to be applied at both the resection and donor site level. These are fixed to the bone with screws and play an important role in determining the osteotomy and inclination of the cutting instruments (Figs 2-4). In this way, both the resection and the bone flap modelling are performed and adhere to pre-surgical planning. On the guides the exact angle and location for each fixation screw for more efficient drilling can also be determined.

Computer-aided design and computer assisted manufacturing (CAD/CAM)

CAD and virtual planning software has considerably enhanced surgical precision and shortened operative times, but the utilisation of plates with universal shapes is ubiquitous for bone fixation. Conforming these plates to specific defects can be a technically demanding and time-consuming process, particularly for complex cases. The repetitive bending of the plates may also result in increased fatigue and less resistance to corrosion, increasing the risk of plate fracture. Additionally, inappropriate selection of plate size or improper placement can create stress concentrations and is a crucial risk factor ^2,15-17. According to the literature, it is reported that plate fractures occur in 2.9%-10.7% of cases, with most occurring within 2 years after surgery, and often within less than 6 months ². These fractures cause significant discomfort for patients and typically require a new surgical procedure for repair. In addition to plate fractures, other commonly reported complications related to reconstruction plates include screw loosening, fracture, bone resorption, dehiscence, infection, skin or mucosal perforation, and plate exposure. To address these complications, patient-specific implants have been developed, which are prefabricated to fit the specific shape of the ideal reconstructed jaw. The use of CAD/CAM technologies, such as 3D printing or computer numerical control machining, allows for the precise fabrication of patient-specific implants (PSI) or prosthetics, ensuring that the design created in CAD is accurately translated into a physical object (Fig. 5). Commonly used PSIs in jaw reconstruction include titanium reconstruction plates, contour augmentation with porous polyethylene (e.g., Medpor), or polyetheretherketone. In post-oncologic reconstruction, titanium plates are used almost exclusively ^2,16,18. However, the use of other materials or various types of prostheses for the reconstruction of the midface, mandible, and temporomandibular joint is currently limited to jaw defects after the ablation of benign lesions with a good soft tissue envelope. The long-term use and exposure of prostheses, as well as the fatigue and fracture of prostheses after radiation therapy, remain unsolved problems.

CAD/CAM systems advantages

CAD/CAM systems offer several advantages in bone reconstruction following head and neck tumour resection.

Precision and customisation

CAD/CAM systems offer a high degree of precision and customisation in surgical planning. Measuring the adherence between the virtual planning and the transposition on the operating field, Zavattero et al. ¹⁹ observed a good degree of accuracy, particularly in patients requiring large, complex mandibular reconstructions using multiple fibular segments. Metzler et al. ⁹ retrospectively reviewed 20 CT scans from 10 patients who underwent mandibular reconstructions using fibular flaps. The dimensions of the fibular segments after osteotomy did not differ from those of the preoperative virtual surgical plans. When comparing patients reconstructed with and without CAD/CAM systems, although there is some variation in the proposed parameters, the literature generally agrees that CAD/CAM-guided reconstruction provides greater accuracy and precision compared to traditional methods.

Reduction of surgical times

Preoperative planning utilising CAD/CAM technology has been demonstrated to significantly decrease surgical time. By creating comprehensive surgical plans, surgeons can minimize the need for adjustments during surgery, potentially shortening the overall duration of the procedure. A number of studies have compared the intraoperative and ischaemia times of conventional surgery versus CAD/CAM surgery, consistently showing that the latter results in significant reductions ^2,10-13. A systematic review by Padilla et al. ¹⁰ found that the use of CAD/CAM technology resulted in an mean decrease in operative time of 65.3 minutes. Additionally, reductions in operative time have been shown to lead to a corresponding decrease in the length of hospital stays, with an average reduction of 2 days ².

Improved functional and aesthetic outcomes

It has been demonstrated that the enhanced accuracy of reconstruction resulting from the use of CAD/CAM technology can lead to a reduction in intersegmental bone gaps, more predictable reconstruction contours and bone healing ^2,5,14. These improvements can simplify the dental rehabilitation process. Although there may be some variations in the parameters proposed, the literature generally agrees that CAD/CAM-guided reconstruction provides greater accuracy and precision compared to traditional methods ². The restoration of the proper shape and correct relationships between the mandibular and maxillary bones can result in adequate support for the soft tissues of the face, restoration of symmetry, and in cases of maxillary defects, support for the nasal pyramid and orbital content ^15-17. Furthermore, the restoration of normal occlusal relationships and the position of the mandibular condyles in the glenoid fossa is crucial.

Reduced rate of complications

With accurate preoperative planning, CAD/CAM systems can help minimise complications during surgery by ensuring the precise fit of reconstructed bone, which can decrease the risk of postoperative issues such as infections or implant failure ^18-20. The shorter surgical times associated with CAD/CAM systems have been shown to reduce patient morbidity and complication rates, including the risk of venous thromboembolism (VTE), infection, wound breakdown, and delirium ². Additionally, reductions in free flap ischaemia time have been associated with fewer postoperative complications, such as surgical site infections and partial or complete flap failure. The time-saving benefits of CAD/CAM systems may also be attributed to the ability to perform simultaneous ablation and free flap harvest, minimise intraoperative plate contouring, and perform osteotomies prior to ischaemia in fibular free flap reconstruction using cutting guides.

Safe oncological margins

CAD/CAM systems require the establishment of oncologic margins preoperatively in order to produce anatomic models and cutting guides. While there was initial uncertainty regarding the control of locoregional disease with preplanned margins, several studies have shown similar rates of negative intraoperative and final margins, as well as short and long-term recurrences ^2,21. Oncological safety of the method is now established, but requires presurgical evaluation of margins on recent CT and MRI, that too much time does not pass between planning and surgery, accurate correlation of the clinical and radiological data, and preoperative collaboration of ablative and reconstructive surgeons via videoconference. Furthermore, the use of VP may also allow for clearer determination of margins on the software generated or 3D printed anatomic model for difficult to reach areas, such as the parapharyngeal space, skull base, and orbit.

Patient-specific implants

Customised plates are designed during preoperative VP videoconferences, in accordance with specifications provided by the reconstructive surgeon, regarding the desired number, angle, and location of screw holes, plate contour, and thickness. Advancements in manufacturing techniques have enabled the production of custom plates through both conventional milling and 3D printing of conventional titanium alloys. A comparison of 142 patients who underwent segmental mandibulectomy with fibular free flap reconstruction, with either pre-bent/preformed plates or custom-printed plates, revealed lower complication rates in the latter group, characterised by fewer hardware explantations and less need for reoperations^11,14,20. Furthermore, the use of customised contoured plates eliminates the requirement for bending, which may reduce the risk of plate fracture due to over-bending.

Enhanced communication and education

CAD/CAM systems play a crucial role in enhancing communication between surgical teams, as well as with the patient. The visualisations and 3D models generated by these systems are instrumental in educating and informing patients about the procedure, which enables them to be more involved in the process.

Concerns on CAD/CAM systems

It is imperative to note that while the benefits of CAD/CAM systems have been well-documented in recent years, there are still several drawbacks that must be taken into account when considering their implementation.

Costs

The use of CAD/CAM technology for jaw reconstruction carries recognisable benefits, but its widespread implementation is hindered by its cost, which ranges from € 4000 to € 6000 per patient. Specifically, the expenses associated with materials and the need for third-party companies to develop models and cutting guides contribute to these elevated costs. While the majority of studies confirm these figures, it is important to consider the cost savings achieved through reduced surgical times and the decreased incidence of complications when utilising CAD/CAM technology. Several authors, including Rodriguez-Arias ²², Bolzoni ²⁰, and Tarsitano ³, have reported similar total costs for patients treated with and without CAD/CAM technology. Furthermore, although the cost difference of the plates was substantial ²³, the use of CAD/CAM technology led to a decrease in complications and improved outcomes, thereby offsetting this difference.

Poor pre-surgical planning modifiability

Another crucial factor to consider is the difficulty in modifying the plan after the models and plates have been manufactured. Most resections can be performed with adequate margins based on preoperative imaging; however, in cases where cancer progresses and a more aggressive resection is needed, modification of the cutting guides and titanium plate can be extremely difficult and may require a freehand approach if the guides and plate are rendered unusable. Under these circumstances, the operative time may be prolonged if the plans are abandoned; in addition, the costs of the model and plate are wasted. In two studies, Wilde et al. ^24,25 reported the need for intraoperative changes in plans in 19% and 17.6% of cases. This problem can partly be overcome by adequate and careful planning based on recent examinations and by not allowing too much time to pass between intervention and presurgical planning.

The poor moldability of custom-made plates also prevents any imperfections in the planning from being corrected, nullifying the advantages of the method.

Non-applicability to soft tissues reconstruction

Defects resulting from oncological resections often involve composite bone and soft tissues. However, current CAD/CAM systems are unable to plan for soft tissues reconstruction, since their shape and size can significantly change over time, especially in patients undergoing postoperative adjuvant radiation therapy. This can reduce the functional and aesthetic benefits offered by these technologies.

Another factor to consider is the potential for imbalance of masticatory muscles after jaw resection and reconstruction, which can lead to temporo-mandibular joint dislocation, reduced chewing efficiency, and a diminished quality of life. Therefore, the accurate location of the reconstructed bone by itself is insufficient to determine the final outcome.

Time

One of the limitations of virtual surgical planning systems is the challenge of scheduling a mutually convenient time for all parties to meet and discuss the reconstruction. These planning sessions can last one hour, and the time required for such sessions may not always be compatible with daily clinical schedules. However, improvements are being made to address this issue, as both surgeons and engineers are becoming more confident in the method and reducing the time needed. Furthermore, the time between planning and the arrival of the material, which is typically within two weeks, may also be a source of doubt. Specifically, this timing may not always be compatible with the treatment times of patients with oncological problems.

In-house CAD/CAM laboratories

In the recent literature and daily routine, two developments have emerged as potential solutions to the challenges of cost, dependence on industries, time constraints, and low flexibility in planning: the establishment of low-cost solutions for the in-house production of cutting guides using open-source software and in-house printers, and the use of partially adjustable resection aids ^2,4,5.

An in-house CAD/CAM system for head and neck reconstruction offers numerous benefits to medical facilities and surgical teams. The implementation of such a system within a hospital or clinic requires the establishment of the necessary hardware, software, and expertise. Although the initial costs and time investment in training may be significant, the system offers several advantages, including:

1. immediate access and control: with an in-house CAD/CAM system, surgeons and medical staff have immediate access to the technology, which can be critical in emergency cases or for making quick adjustments to surgical plans;
2. customisation and tailored solutions: an in-house system allows for greater control over the design and customisation process, enabling surgeons to oversee the creation of patient-specific models and implants for a high level of accuracy and customisation;
3. expedited processing: having the CAD/CAM system on-site allows for a potentially faster turnaround time in creating models, designing implants, and planning surgeries. This can reduce the overall time from diagnosis to surgery.
4. long-term cost savings: although the initial investment in setting up an in-house CAD/CAM system may be substantial, it may prove to be cost-efficient in the long run. It can potentially reduce expenses associated with outsourcing services to external facilities and offer greater control over expenses;
5. improved quality control: with direct oversight, the system enables better quality control. Surgeons can ensure that the models and implants meet their standards and specific patient requirements.

However, establishing an in-house CAD/CAM system requires dedicated space, initial investment in equipment, software, and trained personnel to operate the system. Regular maintenance and updates are also necessary to ensure optimal functionality. To date, the production of prostheses and implantable materials is strictly regulated on an international level, which renders it impossible to print plates or prostheses in-house. This must still be entrusted to specialised companies.

Future perspectives

According to most authors, possible future developments are to be found in three main sectors: development of biomaterials, integration between CAD/CAM systems and other technologies and further development of software.

Biomaterials development 2,5,7

1. Bioresorbable materials: advances in bioresorbable materials are being pursued for their potential to create temporary implants that reabsorb as the patient recovers, reducing the need for additional surgeries to remove them.
2. Biologically active materials: materials that promote tissue regeneration or enhance bone growth are under investigation. These materials could actively contribute to the healing process and encourage integration with surrounding tissues.
3. 3D-printed custom implants: innovations in 3D printing technology are enabling the creation of highly customised, patient-specific implants using biocompatible materials. This area is expected to experience substantial growth, leading to improved integration with the patient’s anatomy.

Integration of CAD/CAM systems with other technologies 2,14

1. Virtual reality (VR) and augmented reality (AR): the integration of CAD/CAM systems with VR/AR technologies has the potential to enhance preoperative planning by allowing surgeons to visualise and simulate procedures in a virtual environment.
2. Artificial intelligence (AI): AI has the potential to optimise surgical planning and improve decision-making by analysing vast amounts of patient data and provide insights for personalised treatment plans.
3. Telemedicine and collaborative platforms: the integration of CAD/CAM systems with telemedicine platforms could enable remote consultation and collaboration among surgeons worldwide, fostering sharing of knowledge and enhancing expertise.

Conclusions

CAD/CAM systems are now widely used in the restoration of bone defects following oncological resection for head and neck tumours. This technology has demonstrated exceptional reliability in terms of accuracy, precision and predictability, leading to improved outcomes, reduced surgical times and decreased complications. Barriers such as high costs and delays in manufacturing may be addressed through the development of in-house software and workflows. Further limitations are also constituted by the non-applicability to soft tissue repair and need for pre-formed or custom-made osteosynthesis plates, in the latter case with a further increase in costs. Despite these limitations, CAD/CAM technology has a strong indication in the following cases: total or subtotal mandibular defects, total or subtotal maxillary defects, and secondary reconstructions.

Conflict of interest statement

The authors declare no conflict of interest.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Author contributions

CC, AM, FC, OI: conception and design of the work, research on PubMed, literature review, drafting of the article; FB, FM, SC: contribution to the concept and design of the article, critical revision.

Ethical consideration

Not applicable

Figures and tables

Figure 1.Starting from preoperative CT imaging (a) a 3D anatomical model of the bone involved is created, allowing a direct visualisation of the lesion and the pre-bending of the plate (b). The latter will then be used to model and fix the bony segments of the fibula flap to the mandibular stumps (c).

Figure 2.Virtual simulation systems allow the pre-surgical planning of the resection margins of an osteolytic lesion, including direction and orientation of the osteotomy lines (a). The virtual is transposed to real thanks to the design (b) and printing of cutting guides (c).

Figure 3.The virtual procedure continues with the planning of the reconstructive phase. Also in this case the cutting guides are virtually designed (a) and molded to be fixed to the iliac crest (b). Softwares allow to define the dimensions, number and orientation of the bone segments used for reconstruction both in the virtual (c) and in the real fields (d).

Figure 4.Thanks to pre-surgical planning it is possible to obtain a faithful reconstitution of the normal anatomy, as pre- (a) and postoperative orthopantomographies (b) show.

Figure 5.Starting from virtual planning (a), industrial 3D printings can produce custom made plates (b). Their characteristics are based on what was decided during the presurgical phase regarding dimensions, thickness and number and position of the screw holes.

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