3D-Printed Patient-Specific Surgical Plates Versus Conventional Surgical Plates in Jaw Reconstruction

This randomised controlled clinical trial was based on our previous clinical trial "Three-Dimensional Printing of Patient-Specific Titanium Plates in Jaw Surgery: A Pilot Study" (HKU/HA HKW IRB, No. UW 16-315; registered in ClinicalTrials.gov with a No. of NCT03057223; supported by HMRF Project no.: 05161626).

Over the past few decades, autologous vascularized bone flaps have become the preferred choice for head and neck reconstruction. The anastomosed blood supply endows vascularized bone flaps with improved survival rate and inherent anti-infection performance. Along with the development of microvascular surgery, surgeons are seeking more accurate reconstruction to enhance better aesthetic and functional outcomes. However, a main disadvantage of autologous bone flaps is the mismatch in the shape of donor bone, which need to be cut and trimmed to fit the defects and better restore the natural appearance. Much efforts have been devoted to facilitate bone manipulations, and then the computer-assisted surgery (CAS) emerged in the 21st century as a viable option. In CAS, surgeons do virtual plans in computer, which then guide the precise harvest and arrangement of bone segments for repairing defects in the operating theatre. Bone segments can be fine-navigated to best restore the original skeleton. In previous researches, various devices have been developed to navigate bone segments according to virtual plans, including cutting templates, skull models, and surgical navigation system.

However, the missing link between bone navigation and accurate reconstruction is the plate fixation procedure. In a conventional manner, bone segments are fixed using commercial off-the-shelf titanium plates, which should be manually bent and twisted to fit bone anatomy. The manual contouring process is often tedious and technique-demanding, and adversely affect the precise location of bone segments. What's worse, repeated bending can even lead to poor fatigue performance. The disadvantages of conventional surgical plates make it necessary to develop patient-specific surgical plates. Compared to conventional plates, patient-specific surgical plates are designed and manufactured in 3D structures aligned with individual bone contours. Instead of contouring plates based on anatomical structure of bones in conventional plates, patient-specific surgical plates navigate the folding and precise location of bone segments, and hopefully improve the accuracy of reconstruction. Meanwhile, since no plate bending is required, patient-specific surgical plates can be used to optimize bone reconstruction in a more efficient and standardized manner.

In recent years, with the rapid development of additive manufacturing (3D printing), it is now feasible to manufacture patient-specific metal implants with topologically optimized structures. Many efforts have been made to develop porous bone scaffolds for regenerative medicine, which are endowed with customized porosity to achieve optimal biomechanical properties. However, although additively manufactured bone scaffolds demonstrate excellent performance in some complicated cases, they still cannot replace the dominant role of autologous vascularized bone flaps in head and neck reconstruction. Therefore, it is of crucial importance to explore the application of additive manufactured (3D printed) patient-specific surgical plates, albeit not much research has been done in this direction.

In our previous study (HKU/HA HKW IRB, No. UW 16-315) supported by Health and Medical Research Fund (Project no.: 05161626), the investigators have successfully manufactured patient-specific titanium plates with high precision through selective laser melting (SLM) technology, which is a high-tech 3D printing technology that fully melts titanium powders into complete entities in the layer by layer manner. SLM enables the fabrication of patient-specific titanium surgical plates with tailored structures and outstanding biomechanical properties. Our results showed promising clinical outcomes in the application of 3D printed patient-specific titanium plates in head and neck reconstruction. Furthermore, the investigators did a retrospective study comparing the patients who had undergone jaw reconstructive surgery using 3D printed patient-specific surgical plates versus conventional titanium plates and the result showed superior accuracy of reconstruction outcomes in the study group with the use of 3D printed patient-specific surgical plates. However, there were significant limitations in our study. First, as a retrospective study, the innate flaw of study design was unavoidable, such as selection bias. Second, there was significantly difference in follow-up periods between the study group and control group. The imaging data used for accuracy analysis were obtained during different post-operative periods, which compromised the final outcomes. Finally, surgical efficiency endpoints, such as operation time, blood loss, and post-operative hospital stay, which could be significantly affected by multiple confounding factors, are difficult to control by retrospective study design. Hence, there is still lack of high-level evidence concerning the advantages of 3D printed patient-specific surgical plates in head and neck reconstruction. Whether 3D printed patient-specific surgical plates improve surgical accuracy and efficiency compared to conventional plates in computer assisted jaw reconstruction should be further investigated before large-scale clinical application.

Therefore, the investigators aim to evaluate surgical accuracy and efficiency of computer-assisted jaw reconstruction using 3D-printed patient-specific titanium surgical plates versus conventional plates in a prospective randomised controlled clinical trial. Our study is expected to provide high-level evidence to push forward the popularity of using 3D medical printing new technology in the surgical field.

Methods

The methodology has already been set up and has been proved feasible in our earlier studies. The PI has been working on computer aided surgical simulation, virtual planning, and 3D printed surgical templates in the maxillofacial surgery for several years and has published a series of articles.

1. Computer-assisted Surgery The CAS techniques used in head and neck reconstruction are well established in our unit and have been described previously. Briefly, CAS is composed of three main phases: the pre-operative phase of the virtual surgery and 3D printing of patient-specific devices, intra-operative phase involving precision-enhanced surgery to install the patient-specific devices, and post-operative phase involving the accuracy analysis. The patient-specific devices can include cutting guides, positioning guides, and the patient-specific titanium plates. In our trial, the study group will use cutting guides and patient-specific titanium plates, whereas the control group will use cutting guides, positioning guides, and conventional plates. In the pre-operative phase, the virtual surgery will be performed by surgeons using the ProPlan CMF 2.0 software (Materialise, Leuven, Belgium). The patient's CT data is initially segmented to rebuild 3D virtual models of the maxilla or mandible using ProPlan's interactive interface. Next, bone resection is performed in the 3D models for en bloc removal of any tumours. Meanwhile, bone grafts are harvested from fibula or iliac crest to repair defects and restore the normal appearance. Finally, the virtually reconstructed maxilla or mandible is used to design patient-specific devices to navigate the bone segments.
2. Additive Manufacturing of Patient-specific Devices Compared to the conventional approach of designing patient-specific devices using engineering companies, we have adopt an in-house approach that allow the surgeons to design and manufacture the devices. All patient-specific devices are designed in 3-matic 13.0 (Materialise). Cutting guides, which guide and adapt to bone surface for accurate bone resection, are generated by wrapping to the bone surface. For the study group, patient-specific surgical plates are designed by delineating the plate path on the bone surface, followed by the placement of screw holes. Surgical plates are generated by a built-in command in 3-matic. Next, the surgical plates are fabricated by SLM using grade 2 titanium powder. For the control group, positioning guides will be designed for the bone segment alignment and inset. Both cutting and positioning guides will be additively manufactured by Fused Deposition Manufacturing (FDM) using ULTEM 1010, or by Stereolithography using MED610 resin (Stratasys Ltd, Eden Prairie, MN, USA). Both ULTEM 1010 and MED610 are FDA cleared biocompatible materials usable in high-temperature autoclaving.
3. Surgical Procedures In the present study, all patients in both groups will undergo CAS carried out by the same chief surgeon (PI). During the surgery, patient-specific cutting guides will enable precise jawbone resection and bone flap osteotomy. In the control group, the arrangement of bone segments will be manipulated according to the positioning guide. Bone segments will be stabilized using commercial titanium surgical plates (DePuy Synthes, United States), which are bent manually before fastening with screws. In the study group, patient-specific surgical plates will be designed and fabricated to custom-fit the bone contours of reconstructed maxilla or mandible. The screw holes embedded in cutting guides correspond to the 3D-printed patient-specific surgical plates, which will guide the position of surgical plates and bone segments, thereby facilitating folding, positioning, and fixation of bone segments in the real surgery. Standard peri-operative management will be similar in both groups. Post-operative follow-up will be conducted in a routine manner.
4. Data collection procedures

CT scan will be obtained at baseline (before surgery) and post-operatively (within 1 month after the surgery). The accuracy of reconstruction will be independently assessed by two assessors. Training will be provided using previous cases, and calibration between the two assessors will be done with the aim of achieving over 90% inter-assessor agreement in three consecutive training cases before starting the measurement of subject cases in this study. Other information such as reconstruction time, total operative time, intra-operative blood loss, length of post-operative hospital stay, and post-operative adverse events will be recorded.