3D Sequencing and Protocols in Head and Neck Reconstructive Surgery: Delivering Predictable Results

Predicting disease burden

The advancements in high-definition head and neck imaging modalities have led to a sea change in the accuracy with which the extent of tumour invasion is determined.

With an experienced specialist head and neck radiologist, in combination with a dedicated multidisciplinary team (MDT), it is possible to accurately identify bony invasion using CT and MRI imaging.⁴ Multi-modular imaging increases the accuracy. The extent of the tumour and the size of the tumour can be reliably identified with a 96% accuracy.⁵ Further use of cone beam CT (CBCT) can improve this further.⁶ Through reliably determining tumour burden on multi-planar imaging, we can then accurately predict our resection ahead of time.

Developing high-fidelity and reliable reconstructions

The fibula free flap remains the workhorse of mandibular osseous reconstruction. Over time, modifications and complexity of flap design have improved functional, occlusal and aesthetic outcomes. 3D planning is the latest evolution in surgical technique that can deliver predictable, complex results with high fidelity.

Digital technology facilitates pre-operative surgical planning to a high degree of accuracy. Using 3D reconstructed CT scans, clinicians, working alongside bio-engineers, can design osteotomies to millimetre precision with specific angulations. Importantly, this technology enables multiple theoretical flap designs to be pre-fabricated. Each potential design can be evaluated for its merits and disadvantages. This means that the end design should be consistently the most effective.⁷

Previous publications have demonstrated that 3D planning gives surgeons confidence in increasingly complex reconstructions such as, osteotomies, wedge osteotomies and double-barrels (where two bone segments are placed vertically and soft tissue is rotated).⁸ Previous evidence has shown that this increased complexity with 3D planning has not been associated with an increase in complications.⁹

3D planning has been shown to facilitate dental rehabilitation,¹⁰ and surgeons are able to design the flap with the primary placement of osseo-integrated dental implants. Positioning these implants in the neo-mandible can be complex when considering the native occlusion and the post-operative outcome.

Communication and consent

A less widely discussed benefit of 3D sequencing is the opportunity it affords the patient in the consent process. Comprehending the nature of head and neck resection and reconstruction can be challenging for patients. With the use of this software, images and models can be shown to the patient and can assist in their understanding of the disease, the proposed surgery and it can provide a physical manifestation of the proposed outcome.¹¹

Costs

When considering the costs of 3D sequencing, one must consider the costs of the patient-specific design and manufacture of the implant against costs of a standard plate. While this simple cost would favour the cheaper standard plate, one must also consider other indirect costs.

There is plenty of evidence to demonstrate significant cost savings on reduced operating time, improved accuracy and outcomes of the reconstruction, and thus long-term improved outcomes and cost savings in patient care in the future. For example, reducing returns to theatre or flap adjustments, plate removals or further surgeries.¹² In addition, the improved benefits in dental rehabilitation could reduce costs in the medium to long term for patient care.¹² There is also evidence to suggest that the use of patient-specific implants can reduce the length of inpatient stay, although the mechanism of this is less obvious. Indeed, some authors have argued a cost saving in using 3D reconstruction.¹³

As the technology improves, and uptake becomes widespread, this cost is likely to further reduce. Finally, more evidence is being published that shows that even in resource-limited and strained healthcare infrastructures, 3D prototyping and implants have a worthwhile and cost-effective role to play. For example, one team in Haiti demonstrated a cost-efficient way to provide 3D models and implants for patients with mandibular reconstructions.¹⁴

Planning

3D planned reconstruction of head and neck defects following ablative surgery can be applied in a wide range of suitable cases. While its role primarily applies to mandibular reconstruction using fibula vascularized bone, there is both practical and theoretical evidence to suggest its applicability to any hard or even soft tissue defect.¹⁵

Key in the planning stage is obtaining high-quality DICOM (Digital Imaging and Communication in Medicine) images (0.75-mm thick slices) of both the donor site and resection site. CT angiography should demonstrate good quality arterial supply and venous drainage of the donor site. These images can be manipulated using proprietary software to virtually reconstruct both the donor site and tumour site. Evidence suggests that this pre-operative planning of margins provides at least as good outcomes in terms of recurrence, involved positive margins and patient survival.² The limiting factor is likely to be the ability of imaging to accurately determine tumour burden radiographically. As this technology improves, it may be that this accuracy does too.

Case report

This report describe the case of a 33-year-old previously fit and well woman who presented with a painless right-sided facial swelling for 6 months. CT imaging demonstrated a unicystic mandibular lesion extending from the LR6 to the LL2, with bony expansion and resorption of the roots of multiple teeth. Subsequent biopsy confirmed this as unicystic ameloblastoma.

Resection

Figure 1 shows a 3D reconstruction of fine-cut bone windows of CT facial bones. The ameloblastoma is demonstrated here as a large right mandibular lesion. The orange annotated portion is the planned resection extending from the right sigmoid notch to just proximal to the left mental foramen.

Donor site

The left fibula was planned as the donor site for free flap reconstruction. In Figure 2, four segments can be visualized. This plan enables sufficient protection of the ankle mortis, while taking into consideration the pedicle length required for microsurgical anastomosis.

Reconstruction and osteotomies

Figure 3 outlines the reconstruction. This reconstruction involves eight osteotomies (bony cuts), four bone segments and a double-barrel. Additionally, all these osteotomies are angled, and a further two segments required further adaptation for optimum bony contouring. This number of variables substantially increases the surgical complexity and thus, to ensure reliably good outcomes, with minimal risk, 3D planning is required.

Outcome

Figure 4 demonstrates the implant, which was constructed with a strengthened titanium alloy, and the post-operative outcome. The design of the plate is complex and would not be feasible with standard plates. First, the plate can be designed in such a way as to incorporate the double-barrel segment within a single plate, and secondly, nuanced multi-planar bends enable accurate adaptation to the bone. Both of these increase the strength of the plate, as well as helping close union of the bony segments to ensure good bone healing.

Finally, the plate and screw position can be designed in conjunction to ensure precise angled placement to avoid the inferior alveolar nerve. This minimizes morbidity from nerve injury. This highlights the congruency between the planned reconstruction and post-operative outcome. The double barrel component provides sufficient dento-alveolar height to enable dental rehabilitation.

The future

This case study reflects the current role of 3D planning in hard tissue reconstruction. However, the technology exists for consideration of soft tissue defects. This proof of concept has already been tried by a team in Manchester.¹⁵

Accurate identification of tumour burden is possible with current modalities, and thus it follows that resection margins and defects can be planned. The defect can then be mapped onto the soft tissue donor site of choice to enable highly accurate and complex soft-tissue reconstructions. The role of CT angiography could be incorporated to enable identification of perforator vessels, further increasing microvascular reliability.¹⁶

Image-guided augmented reality is potentially the next frontier in surgical innovation. It may well be that the combination of this augmented reality and pre-operative sequencing could well pave the way for every aspect of surgical management, from incision to closure, to be pre-planned.¹⁷

Summary

Several preliminary conclusions can be made. Pre-operative 3D planning reduces intra-operative time in addition to facilitating accuracy and reproducibility. Computer-assisted surgery is a useful adjunct, and in the authors' experience, has been shown to achieve and improve on the main aims of mandibular reconstruction, which include resection of the defect and restoration of form and function. Stereolithographic models have an important role in craniomaxillofacial surgery. They not only benefit the operating clinician, but further aid doctor–patient communication with direct visualization of anatomical structures. Continuing to develop our understanding of these techniques, will help widen the breadth of its utility, including in resection accuracy, reconstruction and surgical outcomes.