Philipp Juergens

Computer simulation and rapid prototyping for the reconstruction of the mandible.

Augmented-reality environments, that is, computer graphics merged with 3-dimensional representations of anatomic regions generated from imaging modalities (mainly computed tomography [CT] and magnetic resonance imaging), have their background in well-known and well-established conventional image-guided surgery, which we can describe as the “first generation of navigation.” 1-3 Although the surgeon is solely supplied with “information,” this technology significantly expands the range of the intraoperatively available information. Nevertheless, it does not provide any kind of haptic feedback, and the transfer of all the computer information is accomplished manually during the treatment of the patient. Technical progress led to the integration of rapid prototyping techniques (3-dimensional stereolithography) in image-guided surgery workflows and therefore can add “haptic” information to the computerbased visualization. Therefore we can call such approaches the “second generation of navigation.” Simulation and planning of surgical interventions by use of stereolithographic models can contribute to the optimization of treatment and can also enhance quality management in craniomaxillofacial surgery, because the specific anatomic situation of each patient can be comprehensively analyzed preoperatively. Navigation technology enables the precise transfer of the

Odontogenic myxoma: Diagnostic and therapeutic challenges in paediatric and adult patients – A case series and review of the literature

INTRODUCTION Odontogenic myxomas are benign but locally invasive tumours originating from primordial mesenchymal tooth forming tissues which do not metastasise. We present a series of two paediatric and two adult cases and focus on differences in diagnostic and therapeutic approaches between children and adults based on our own experience and a critical review of the literature.

Evaluation of risk of injury to the inferior alveolar nerve with classical sagittal split osteotomy technique and proposed alternative surgical techniques using computer-assisted surgery.

Neurosensory disturbance after sagittal split osteotomy is a common complication. This study evaluated the course of the mandibular canal at three positions using computed tomography (CT), assessed the risk of injury to the inferior alveolar nerve in classical sagittal split osteotomy, based on the proximity of the mandibular canal to the external cortical bone, and proposed alternative surgical techniques using computer-assisted surgery. CT data from 102 mandibular rami were evaluated. At each position, the distance between the mandibular canal and the inner surface of the cortical bone was measured; if less than 1mm or if the canal contacted the external cortical bone it was registered as a possible neurosensory compromising proximity. The course of each mandibular canal was allocated to a neurosensory risk or a non-neurosensory risk group. The mandibular canal was in contact with, or within 1mm of, the lingual cortex in most positions along its course. Neurosensory compromising proximity of the mandibular canal was observed in about 60% of sagittal split ramus osteotomy sites examined. For this group, modified classic osteotomy or complete individualized osteotomy is proposed, depending on the position at which the mandibular canal was at risk; they may be accomplished with computer-assisted navigation.

Three-dimensional imaging of the larynx for pre-operative planning of laryngeal framework surgery

Modern laryngeal framework surgery (LFS) requires an exact understanding of the laryngeal biomechanics and precise pre-operative planning, for which bi-planar imaging is not sufficient. The aim of the study was to test whether MIMICS®, a commercially available software package for three-dimensional (3D) rendering of high-resolution computerised tomography (HRCT), is suitable for 3D imaging of the larynx, analysis of laryngeal biomechanics and pre-operative planning. We examined four cadaver larynx and one patient larynx. In the five larynges, all relevant structures and landmarks could be 3D visualised. Superimposing of two HRCT scans shows that when the arytenoids move from ‘respiration’ to ‘phonation’, they perform a rotating, translating and tilting motion. Moreover, we could demonstrate that the vocal fold elongates by 7% with cricothyroid approximation. We conclude that MIMCS® is well suited for 3D imaging of the larynx, analysis of laryngeal biomechanics and pre-operative planning of LFS procedures.

Facial acquisition by dynamic optical tracked laser imaging: a new approach

Three-dimensional capture of the surface of soft tissue is a desirable support for documentation and therapy planning in plastic and reconstructive surgery concerning the complex anatomy of the face, particularly cleft lip and palate (CLP). Different scanning systems are used for capturing facial surfaces. These systems are mostly based on a static linear measuring arrangement. Established systems work on the basis of coded white light or linear laser triangulation and digital stereophotogrammetric approaches. Shadowing effects occur with these devices. These effects may be avoided by a radical new approach first used in automotive industries that employs a mobile, flexible handheld laser scanner with simultaneous registration by optical tracking. The aim of this study was to assess the suitability of this scanner for surgical procedures on the human face in operating theatre. Five babies aged about 3 months with cleft deformities (one CLP, one bilateral CLP, three isolated cleft lips) were captured directly: twice preoperatively, twice postoperatively and twice after 7 days. An industrial standard specimen and two plaster cast masks of CLP babies were taken and subsequently measured to assess reliability and validity of the device. Masks were measured to reflect the complex surface of the cleft deformity. Data evaluation was done with respect to completeness of the data sets, as well as reliability and validity of the system. Missing data caused by shadowing could be avoided in all images. Even complex areas with undercuts could be reproduced completely and precisely with an accuracy in the sub-millimetre range.

Developing a 3D model of the laryngeal cartilages using HRCT data and MIMICS’s segmentation software

Abstract Discussions relating to the biomechanics of the larynx are still generally controversial. The purpose of this study is to develop a 3D model of the larynx based on high-resolution computer tomography (HRCT) data identifying and visualizing anatomical landmarks and structures of the larynx. We examined four fresh cadaver larynges with HRCT. The DICOM (Digital Imaging and Communication in Medicine) data were post-processed with the software package MIMICS® for three-dimensional visualization. All relevant structures of the laryngeal cartilages could be identified on HRCT and visualized in a 3D model. We conclude that 1) HRCT provides excellent data for three-dimensional visualization of the laryngeal anatomy, and 2) the combined technology of HRCT and MIMICS® is useful to study the biomechanics on 3D images and for preoperative planning of laryngeal framework surgery.

A comparative investigation of bone surface after cutting with mechanical tools and Er:YAG laser.

Despite of the long history of medical application, laser ablation of bone tissue became successful only recently. Laser bone cutting is proven to have higher accuracy and to increase bone healing compared to conventional mechanical bone cutting. But the reason of subsequent better healing is not biologically explained yet. In this study we present our experience with an integrated miniaturized laser system mounted on a surgical lightweight robotic arm.

Missing facial parts computed by a morphable model and transferred directly to a polyamide laser-sintered prosthesis: an innovation study

Mirroring of missing facial parts and rapid prototyping of templates have become widely used in the manufacture of prostheses. However, mirroring is not applicable for central facial defects, and the manufacture of a template still requires labour-intensive transformation into the final facial prosthesis. We have explored innovative techniques to meet these remaining challenges. We used a morphable model of a face for the reconstruction of missing facial parts that did not have mirror images, and skin-coloured polyamide laser sintering for direct manufacture of the prosthesis. From the knowledge gleaned from a data set of 200 coloured, three-dimensional scans, we generated a missing nose that was statistically compatible with the remaining parts of the patients face. The planned prosthesis was manufactured directly from biocompatible skin-coloured polyamide powder by selective laser sintering, and the prosthesis planning system produced a normal-looking reconstruction. The polyamide will need adjustable colouring, and we must be able to combine it with a self-curing resin to fulfil the requirements of realistic permanent use.

A computer-assisted diagnostic and treatment concept to increase accuracy and safety in the extracranial correction of cranial vault asymmetries.

PURPOSE Proteus syndrome is described as a progressive, asymmetric, disproportional overgrowth of various parts of the body. The theory of somatic mosaicism is widely accepted to be the cause of this disease. Affected patients present very heterogeneous symptoms, but in about 30% craniofacial deformities are the leading clinical features. Because no causal therapy exists, treatment options are limited to surgical improvement of functional constraints. MATERIALS AND METHODS A computer-assisted method was used to increase the accuracy and safety of bone removal in the extracranial correction of cranial vault asymmetries. Descriptions of the diagnosis, preoperative planning, and intraoperative management of craniofacial dysmorphia caused by Proteus syndrome in a 6-year-old boy are presented. After computed tomography-based generation of a virtual 3-dimensional (3D) model of the patient and a haptic stereolithographic model to display the special pathology, flow-sensitized 4-dimensional magnetic resonance imaging was performed to clarify the properties of vascular formation inside the hyperostosis. To transfer the mathematically optimized preoperative planning of a new skull shape to the patient, a surgical guide was fabricated by rapid manufacturing. Intraoperative 3D real-time navigation was installed as an additional visualization and security feature. RESULTS The surgery could be performed safely and quickly. Postoperative imaging showed that the surgical plan was realized with high accuracy. CONCLUSION This newly developed and validated method can be successfully implemented in the operating room environment.

Navigation-Guided Harvesting of Autologous Iliac Crest Graft for Mandibular Reconstruction

Osseous reconstructions with free tissue transfer techniques in the facial region are well established and provide satisfactory results. Also, the introduction of new planning and transfer tools has simplified the surgical process for mandibular reconstruction. The reconstruction of the mandible remains very challenging: functional aspects like speech, swallowing, and chewing—with the help of dentures—have to be taken into account in the same way as esthetic aspects of the patient’s facial appearance. Although many authors report very good results using the free fibula flaps, this technology still has some disadvantages. In dentate patients especially with hemimandibulectomy, the gracile fibula bone causes an asymmetric facial appearance and inappropriate load situations between the strong healthy hemimandible and the reconstructed part. This may subsequently lead to complications. The iliac crest bone was reported to be the first choice for these patients. 1-3 For reconstructive surgical interventions with free-fibula flaps, several methods for virtual planning and transfer of the planning to the patient