Physical and statistical shape modelling in craniomaxillofacial surgery: a personalised approach for outcome prediction

Orthognathic surgery involves repositioning of the jaw bones to restore face function and shape for patients who require an operation as a result of a syndrome, due to growth disturbances in childhood or after trauma. As part of the preoperative assessment, three-dimensional medical imaging and computer-assisted surgical planning help to improve outcomes, and save time and cost. Computer-assisted surgical planning involves visualisation and manipulation of the patient anatomy and can be used to aid objective diagnosis, patient communication, outcome evaluation, and surgical simulation. Despite the benefits, the adoption of three-dimensional tools has remained limited beyond specialised hospitals and traditional two-dimensional cephalometric analysis is still the gold standard. This thesis presents a multidisciplinary approach to innovative surgical simulation involving clinical patient data, medical image analysis, engineering principles, and state-of-the-art machine learning and computer vision algorithms. Two novel three-dimensional computational models were developed to overcome the limitations of current computer-assisted surgical planning tools. First, a physical modelling approach – based on a probabilistic finite element model – provided patient-specific simulations and, through training and validation, population-specific parameters. The probabilistic model was equally accurate compared to two commercial programs whilst giving additional information regarding uncertainties relating to the material properties and the mismatch in bone position between planning and surgery. Second, a statistical modelling approach was developed that presents a paradigm shift in its modelling formulation and use. Specifically, a 3D morphable model was constructed from 5,000 non-patient and orthognathic patient faces for fully-automated diagnosis and surgical planning. Contrary to traditional physical models that are limited to a finite number of tests, the statistical model employs machine learning algorithms to provide the surgeon with a goal-driven patient-specific surgical plan. The findings in this thesis provide markers for future translational research and may accelerate the adoption of the next generation surgical planning tools to further supplement the clinical decision-making process and ultimately to improve patients’ quality of life

PARAMETRIZING THE GENIOPLASTY: A BIOMECHANICAL VIRTUAL STUDY ON SOFT TISSUE BEHAVIOUR

Purpose: Sliding genioplasty is used to surgically correct a retruded or misaligned chin: in this procedure, an osteotomy is performed and the bony segment is repositioned. In this study we investigate the effect of surgical parameters (bony segment movement, osteotomy design) on postop soft tissue changes in a patient cohort. Methods: Seven patients were retrospectively recruited. Cone beam computed tomography data were obtained and soft tissue and bone shape reconstructions were performed. 3D models were created and surgical cuts were replicated according to postop scans. Each model was imported in ANSYS 2019R1 (Ansys Inc, USA) for simulation: the effect of variation in osteotomy plane as well as extent of bony segment movement were assessed by means of design of experiment: surgical parameters were varied in a surgically acceptable range and the soft tissue predictions were evaluated as displacement output of five craniometric landmarks. Results: Simulation results show the overall changes of the lower third of the face are sensitive to changes in horizontal and vertical displacement of the bony segment as well as segment rotation. No significant changes in the soft tissue response were to attribute to the osteotomy design. Conclusions: Our results are consistent with experimental findings reported in the literature: when planning genioplasty in orthognathic surgery, particular focus on the segment movement (horizontal translation, vertical translation and rotation), rather than on the design of the osteotomy itself, should be considered

Evaluation Of Facial Soft Tissue Changes In Excessive Gingival Display Cases After Le Forte I Maxillary Impaction Surgery Using 3D Facial Surface Laser Scanner

Introduction: Facial soft tissue changes in relation to hard tissue movements after orthognathic surgery cases is always of concern to patients , surgical and orthodontics teams. The aim of the present study was to assess facial soft tissue changes and stability using 3D facial laser scanner after orthognathic surgery Le Forte I maxillary impaction in excessive gingival display patients. Methods: The subjects consisted of 12 patients with skeletal vertical maxillary excess (VME) causing an aesthetic concern to the patients in the form of “Gummy smile”, who underwent LeFort I osteotomy with maxillary impaction, Three-dimensional images of the patients were acquired with a 3D laser scanner preoperatively and postoperatively. The changes in facial soft tissue were detected using a colour coded map for analysis. Results: Significant change was recorded in the upper lip, alar base, nasolabial fold and nasal tip areas, without specification of this change in direction. Conclusions: The 3D images captured using the laser scanner in this study can be a useful tool for communication with both patients and professionals but cannot be relied upon solely for accurate analysis of the facial soft tissue changes. The colour coded map analysis cannot be relied upon solely as a method of analysis as it lacks an important aspect of the change which is the direction

Evaluation of a custom made anatomical guide for orthognathic surgery

Orthognathic surgery is a routinely used surgical technique for the correction of dento-facial deformities. During a Le Fort I orthognathic procedure the maxilla is surgically separated from the skull and the surgical positioning wafer is placed between the occlusal surfaces of the upper and lower dentition. However, the physiological response to general aesthesia results in loss of muscle tone in the mandible, which has a profound influence on the correct amount of maxillary advancement required. The expertise and visual judgement of the surgeon is relied upon to foresee and eliminate this potential source of error. However, this may not be possible to achieve in all cases, therefore there is a need for a device to guide the surgical position of the maxilla independent of the mandibular dentition. The aim of this study was to design and validate a custom made anatomical repositioning surgical framework for accurately repositioning the maxilla independently of the mandible during a Le Fort I osteotomy. A single plastic anatomical skull was scanned using a helical Computed Tomography (CT) scanner. Utilising 3D manipulation software, forty-three Le Fort I orthognathic surgery movements were planned. A custom made anatomical repositioning guide was designed and 3D printed for all movements. Each guide was used to reposition the maxilla of the physical skull and then laser scanned using a GOM blue light scanner. GOMinspect software was used to compare the planned and physical position of the repositioned maxilla. The results of the experiment were statistically evaluated.Orthognathic surgery is a routinely used surgical technique for the correction of dento-facial deformities. During a Le Fort I orthognathic procedure the maxilla is surgically separated from the skull and the surgical positioning wafer is placed between the occlusal surfaces of the upper and lower dentition. However, the physiological response to general aesthesia results in loss of muscle tone in the mandible, which has a profound influence on the correct amount of maxillary advancement required. The expertise and visual judgement of the surgeon is relied upon to foresee and eliminate this potential source of error. However, this may not be possible to achieve in all cases, therefore there is a need for a device to guide the surgical position of the maxilla independent of the mandibular dentition. The aim of this study was to design and validate a custom made anatomical repositioning surgical framework for accurately repositioning the maxilla independently of the mandible during a Le Fort I osteotomy. A single plastic anatomical skull was scanned using a helical Computed Tomography (CT) scanner. Utilising 3D manipulation software, forty-three Le Fort I orthognathic surgery movements were planned. A custom made anatomical repositioning guide was designed and 3D printed for all movements. Each guide was used to reposition the maxilla of the physical skull and then laser scanned using a GOM blue light scanner. GOMinspect software was used to compare the planned and physical position of the repositioned maxilla. The results of the experiment were statistically evaluated

From bench to bedside - current clinical and translational challenges in fibula free flap reconstruction.

Fibula free flaps (FFF) represent a working horse for different reconstructive scenarios in facial surgery. While FFF were initially established for mandible reconstruction, advancements in planning for microsurgical techniques have paved the way toward a broader spectrum of indications, including maxillary defects. Essential factors to improve patient outcomes following FFF include minimal donor site morbidity, adequate bone length, and dual blood supply. Yet, persisting clinical and translational challenges hamper the effectiveness of FFF. In the preoperative phase, virtual surgical planning and artificial intelligence tools carry untapped potential, while the intraoperative role of individualized surgical templates and bioprinted prostheses remains to be summarized. Further, the integration of novel flap monitoring technologies into postoperative patient management has been subject to translational and clinical research efforts. Overall, there is a paucity of studies condensing the body of knowledge on emerging technologies and techniques in FFF surgery. Herein, we aim to review current challenges and solution possibilities in FFF. This line of research may serve as a pocket guide on cutting-edge developments and facilitate future targeted research in FFF

PRELIMINARY FINDINGS OF A POTENZIATED PIEZOSURGERGICAL DEVICE AT THE RABBIT SKULL

The number of available ultrasonic osteotomes has remarkably increased. In vitro and in vivo studies have revealed differences between conventional osteotomes, such as rotating or sawing devices, and ultrasound-supported osteotomes (Piezosurgery®) regarding the micromorphology and roughness values of osteotomized bone surfaces. Objective: the present study compares the micro-morphologies and roughness values of osteotomized bone surfaces after the application of rotating and sawing devices, Piezosurgery Medical® and Piezosurgery Medical New Generation Powerful Handpiece. Methods: Fresh, standard-sized bony samples were taken from a rabbit skull using the following osteotomes: rotating and sawing devices, Piezosurgery Medical® and a Piezosurgery Medical New Generation Powerful Handpiece. The required duration of time for each osteotomy was recorded. Micromorphologies and roughness values to characterize the bone surfaces following the different osteotomy methods were described. The prepared surfaces were examined via light microscopy, environmental surface electron microscopy (ESEM), transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM) and atomic force microscopy. The selective cutting of mineralized tissues while preserving adjacent soft tissue (dura mater and nervous tissue) was studied. Bone necrosis of the osteotomy sites and the vitality of the osteocytes near the sectional plane were investigated, as well as the proportion of apoptosis or cell degeneration. Results and Conclusions: The potential positive effects on bone healing and reossification associated with different devices were evaluated and the comparative analysis among the different devices used was performed, in order to determine the best osteotomes to be employed during cranio-facial surgery

Role of Mimics a Cad Software in 3D Reconstruction of CT Data in Oral and Maxillofacial Surgery

INTRODUCTION: Ever since radiations became a part of diagnosis after the discovery of X- rays by roentgen, it has undergone so many advances and the biggest leap of them all is the transition from 2D to 3D. 3D visualization and diagnosis has been made possible by computed tomography. With the arrival of 3D in radiography, the spectrum of use has widened in that it is not only being used for visualization, there is also use of the 3 dimensional images in diagnosing, treatment planning and surgical simulation which is now becoming a more popular method. Technological advances in computerized tomography (CT) have reduced time for data acquisition and thereby reduce the exposure time and the radiation risk for the patient. Now CT data can be exported in DICOM (Digital Imaging and Communication) format which is a format accepted universally by most of the softwares for reconstruction so that CT images may be economically and quickly generated using the CAD software. With Helical CT a single exposure is enough to obtain reconstructed images in all the 3 planes, Axial, Coronal and sagittal. 3D CT was judged superior to multiplanar two-dimensional CT. CT data can be exported into a CD in DICOM format. This data can be reconstructed into a 3D virtual object/model using various softwares. In our department Materialise Mimics is used for the reconstruction of CT data, visualizing, planning and surgical simulation. AIM AND OBJECTIVE: The purpose of the study is to evaluate the efficacy of Mimics a medical based CAD software in 3D reconstruction of CT data, visualization, surgical simulation and physical model fabrication which can be used in Oral and Maxillofacial Surgery. MATERIALS AND METHOD: This study was done in the department of Oral and MaxilloFacial Surgery, Ragas Dental College and Hospital, Uthandi, Chennai. Period of study was done during September 2008 to July 2010. CT was taken for selective patients. A CAD based medical software MIMICS (Materialise, Leuven, Belgium). is used for 3D reconstruction of the acquired CT data. CT protocol. CT Scan parameter for all the patients were as follows, Vertex to Manubrium, 130 kV and 81 mA/s, Slice increment 0.5mm, Width 512 pxl, Height 512 pxl, Pixel size .500 mm, Gantry tilt 0.00, Algorithm H70s. CONCLUSION: The data produced by the CT machines are a series of images. These images are printed on sheets and are viewed as conventional 2D images only and are not interactive. But through this software the CT data is now very interactive. A powerful processor, large virtual memory of the computer and dedicated graphics card is required. This software provides a better visualization of the anatomy and pathology, compared to conventional CT images. Accurate measurement between points and measuring of angles is possible with this software. Osteotomy, distraction and other surgical simulation can be done with this software. Splints templates and guides for intraoperative use can be fabricated. This software eliminates cumbersome procedures to the patient like facebow transfer and impression making. It is a good learning tool as it gives exact details of the anatomy. From this study we conclude that MIMICS a medical based CAD software is a very efficient tool in Visualization, Diagnosis, Treatment planning, Surgical Simulation and fabrication of Templates for intraoperative use in Oral and MaxilloFacial Surgery

Optimization of craniosynostosis surgery: virtual planning, intraoperative 3D photography and surgical navigation

Mención Internacional en el título de doctorCraniosynostosis is a congenital defect defined as the premature fusion of one or more cranial sutures. This fusion leads to growth restriction and deformation of the cranium, caused by compensatory expansion parallel to the fused sutures. Surgical correction is the preferred treatment in most cases to excise the fused sutures and to normalize cranial shape. Although multiple technological advancements have arisen in the surgical management of craniosynostosis, interventional planning and surgical correction are still highly dependent on the subjective assessment and artistic judgment of craniofacial surgeons. Therefore, there is a high variability in individual surgeon performance and, thus, in the surgical outcomes. The main objective of this thesis was to explore different approaches to improve the surgical management of craniosynostosis by reducing subjectivity in all stages of the process, from the preoperative virtual planning phase to the intraoperative performance. First, we developed a novel framework for automatic planning of craniosynostosis surgery that enables: calculating a patient-specific normative reference shape to target, estimating optimal bone fragments for remodeling, and computing the most appropriate configuration of fragments in order to achieve the desired target cranial shape. Our results showed that automatic plans were accurate and achieved adequate overcorrection with respect to normative morphology. Surgeons’ feedback indicated that the integration of this technology could increase the accuracy and reduce the duration of the preoperative planning phase. Second, we validated the use of hand-held 3D photography for intraoperative evaluation of the surgical outcome. The accuracy of this technology for 3D modeling and morphology quantification was evaluated using computed tomography imaging as gold-standard. Our results demonstrated that 3D photography could be used to perform accurate 3D reconstructions of the anatomy during surgical interventions and to measure morphological metrics to provide feedback to the surgical team. This technology presents a valuable alternative to computed tomography imaging and can be easily integrated into the current surgical workflow to assist during the intervention. Also, we developed an intraoperative navigation system to provide real-time guidance during craniosynostosis surgeries. This system, based on optical tracking, enables to record the positions of remodeled bone fragments and compare them with the target virtual surgical plan. Our navigation system is based on patient-specific surgical guides, which fit into the patient’s anatomy, to perform patient-to-image registration. In addition, our workflow does not rely on patient’s head immobilization or invasive attachment of dynamic reference frames. After testing our system in five craniosynostosis surgeries, our results demonstrated a high navigation accuracy and optimal surgical outcomes in all cases. Furthermore, the use of navigation did not substantially increase the operative time. Finally, we investigated the use of augmented reality technology as an alternative to navigation for surgical guidance in craniosynostosis surgery. We developed an augmented reality application to visualize the virtual surgical plan overlaid on the surgical field, indicating the predefined osteotomy locations and target bone fragment positions. Our results demonstrated that augmented reality provides sub-millimetric accuracy when guiding both osteotomy and remodeling phases during open cranial vault remodeling. Surgeons’ feedback indicated that this technology could be integrated into the current surgical workflow for the treatment of craniosynostosis. To conclude, in this thesis we evaluated multiple technological advancements to improve the surgical management of craniosynostosis. The integration of these developments into the surgical workflow of craniosynostosis will positively impact the surgical outcomes, increase the efficiency of surgical interventions, and reduce the variability between surgeons and institutions.Programa de Doctorado en Ciencia y Tecnología Biomédica por la Universidad Carlos III de MadridPresidente: Norberto Antonio Malpica González.- Secretario: María Arrate Muñoz Barrutia.- Vocal: Tamas Ung