Arne Wagner

Quantitative analysis of factors affecting intraoperative precision and stability of optoelectronic and electromagnetic tracking systems.

This study aims to provide a quantitative analysis of the factors affecting the actual precision and stability of optoelectronic and electromagnetic tracking systems in computer-aided surgery under real clinical/intraoperative conditions. A phantom-skull with five precisely determined reference distances between marker spheres is used for all measurements. Three optoelectronic and one electromagnetic tracking systems are included in this study. The experimental design is divided into three parts: (1) evaluation of serial- and multislice-CT (computed tomography) images of the phantom-skull for the precision of distance measurements by means of navigation software without a digitizer, (2) digitizer measurements under realistic intraoperative conditions with the factors OR-lamp (radiating into the field of view of the digitizer) or/and handling with ferromagnetic surgical instruments (in the field of view of the digitizer) and (3) point-measurements to analyze the influence of changes in the angle of inclination of the stylus axis. Deviations between reference distances and measured values are statistically investigated by means of analysis of variance. Computerized measurements of distances based on serial-CT data were more precise than based on multislice-CT data. All tracking systems included in this study proved to be considerably less precise under realistic OR conditions when compared to the technical specifications in the manuals of the systems. Changes in the angle of inclination of the stylus axis resulted in deviations of up to 3.40 mm (mean deviations for all systems ranging from 0.49 to 1.42 mm, variances ranging from 0.09 to 1.44 mm), indicating a strong need for improvements of stylus design. The electromagnetic tracking system investigated in this study was not significantly affected by small ferromagnetic surgical instruments.

Preoperative stereolithographic model planning for primary reconstruction in craniomaxillofacial trauma surgery

High precision anatomical facsimile models of the patients skull, individually produced by stereolithography, have been used in the preoperative planning in 16 patients with acute craniomaxillofacial trauma. In late primary repair, when open reduction and internal fixation had to wait for a decrease in facial swelling or cerebral oedema, computer-aided surgery has proven to be useful in terms of facilitating anatomical reduction, minimizing surgical approaches, saving operating time and leading to improved postoperative results, which may reduce the number of secondary corrections of post-traumatic deformities.

Fixation of zygomatic fractures with a new biodegradable copolymer osteosynthesis system. Preliminary results.

In a prospective study, a new biodegradable osteosynthesis material for the facial skeleton has been used in 27 patients with zygomatic fractures. In the six-month follow-up period, the first ten patients showed clinically and radiologically uneventful healing of bone. There were no implant-related complications. The main advantages of the new material are its malleability when heated, enabling fast adaptation to the bone surface, and the avoidance of a second operation for implant removal.

Colour stereolithography for planning complex maxillofacial tumour surgery

High-precision anatomical facsimile models of the patients skulls, individually produced by colour stereolithography, were used in the preoperative planning for seven patients with complex maxillofacial tumours. Selectively coloured models facilitated the management of ablative surgery and reconstructive procedures as well. The indicators for preoperative colour stereolithographic model planning concerning maxillofacial tumour surgery are discussed.

Clinical experience with interactive teleconsultation and teleassistance in craniomaxillofacial surgical procedures

PURPOSEnThe objective of this study was to evaluate the clinical value and feasibility of surgical telenavigation and teleassistance technology in the field of craniomaxillofacial surgery.nnnMATERIALS AND METHODSnThe technology is based on the principles of augmented reality environment technology and remote stereotactic visualization. A consultant surgeon in a remote location receives video, audio, and stereotactic navigation data from the operation site almost in real-time and, using a head-mounted display, is emerged in the surgical augmented reality environment. By telepresence or teleconsultation, the composite images and superimposed graphics (instruments, target structures, landmarks, contours) can be seen and discussed in connected clinics with the possibility of interactive manipulation and assistance.nnnRESULTSnInteractive teleassistance was used in 27 cases of various types craniomaxillofacial surgery. The principles of computer-aided telenavigation were applied successfully. Technical problems in 6 cases did not cause a breakdown of overall system performance.nnnCONCLUSIONnTeleconsultation with remote experts is a useful tool, although some shortcomings exist. The financial and personal effort involved is considerable.

Recurrent mandibular dislocation under neuroleptic drug therapy, treated by bilateral eminectomy

Acute mandibular dislocations caused by extrapyramidal syndromes under neuroleptic therapy have often been reported in the literature. However, the success of surgical therapy for recurrent mandibular dislocation in patients under long-term neuroleptic therapy has been discussed controversially. In our opinion, modifications in drug therapy--including the administration of so-called atypical neuroleptics--should be considered before advocating surgery. If the revised therapeutic approach proves to be unsuccessful because of psychotic relapse or persistence of extrapyramidal symptoms, good operative results may be achieved by bilateral eminectomy as reported on three psychiatric patients in this paper. In order to avoid postoperative subluxation and internal derangement due to increased muscular tension under chronic neuroleptic therapy, as much bone as possible should be removed when performing eminectomy.

The Varioscope AR - A Head-Monted Operating Microscope for Augmented Reality

Inherent to the field of computer-aided surgery (CAS) is the necessity to handle sophisticated equipment in the operating room; an undesired side-effect of this development is the fact that the surgeon’s attention is drawn from the operating field since surgical progress is partially monitored on the computer’s screen. The overlay of computer-generated graphics over a real-world scene, also referred to as augmented reality (AR), provides a possibility to solve this problem. The considerable technical problems associated with this approach such as viewing of the scenery within a common focal range on the head-mounted display (HMD) or latency in display on the HMD have, however, kept AR from widespread usage in CAS. In this paper, the concept of the Varioscope AR, a lightweight head-mounted operating microscope used as a HMD, is introduced. The registration of the patient to the preoperative image data as well as preoperative planning take place on VISIT, a surgical navigation system developed at our hospital. Tracking of the HMD and stereoscopic visualisation take place on a separate POSIX.4 compliant realtime operating system running on PC hardware. While being in a very early stage of laboratory testing, we were able to overcome the technical problems described above; our work resulted in an AR visualisation system with an update rate of 6 Hz and a latency below 130 ms. First tests with 2D/3D registration have shown a match between 3D world coordinates and 2D HMD display coordinates in the range of 1.7 pixels. It integrates seamlessly into a surgical navigation system and provides a common focus for both virtual and real world objects. On the basis of our current results, we conclude that the Varioscope AR with the realtime visualisation unit is a major step towards the introduction of AR into clinical routine.

Treatment of intraosseous high flow arteriovenous malformation of the mandible by temporary segmental ostectomy for extracorporal tumour resection: a case report

We present a case of intraosseous arteriovenous malformation of the mandible with temporary segmental resection, extracorporal removal of the vascular malformation from the osteotomized mandibular bone and intraoperative osteosynthetic replantation of the avascular bony remnant. In a follow-up after 1 year, when removing the titanium miniplates used for osteosynthesis, the mandibular bone was found to have remodelled completely. There is no recurrence of the lesion in a follow-up after 2 years.

Validity of sentinel lymph node (SLN) detection following adjuvant radiochemotherapy (RCT) in head and neck squamous cell carcinoma (HNSCC).

The effect of preoperative radio chemotherapy on lymphatic drainage and intraoperative gamma probe-guided sentinel lymph node detection has yet not been investigated. In this study, we study 13 patients with SCC. Sentinel lymph node (SLN) imaging of the patients was performed using SPECT-CT. Special care was taken to use identical injection sites for both studies. Imaging comprised planar and SPECT, iterative reconstruction and were viewed with the co-registered CT image. The results were validated by comparison with the histological results of intraoperative gamma probe detection and histology of the completed neck dissection. Identical SLNs were found in 6/13 patients. In 2/13 cases SLN biopsies were false-negative. In 4/13 patients preoperative SLN imaging identified more/additional nodes than the initial imaging, whereas fewer nodes were seen in 3/13 patients. Neither the primary tumor site nor the TNM stage was predictive for changes in the lymphatic drainage pattern. No constant effect of irradiation could be demonstrated. Preoperative radio chemotherapy has an unpredictable influence on the lymphatic drainage pattern in HNSCC. Consequently, the intraoperative gamma probe-guided sentinel lymph node detection after radio chemotherapy does not reveal the SLN of carcinogenesis. Thus, we advise fused functional/anatomical imaging (SPECT-CT) before and after radiochemotherapy if the SLN concept is utilized in HNSCC.

Pulsatile expansion therapy for orbital enlargement

Experimental and clinical investigations have documented the modulatory role of the globe in the development of the orbit. In cases of absence or early loss of the globe, severe hypoplasia of the orbit and midface has been reported by several authors. Statical conformers and orbital osteotomies have been used to correct the resulting facial asymmetry. When replacing such conformers by increasingly larger ones, orbital structures are negatively influenced by the repeated trauma of surgical interventions. Simulating the modulatory role of the globe on orbital growth was the objective when developing a pulsatile device for orbital enlargement in cases of anophthalmia and microrbitism. The design, application and preliminary experience with a dynamic, pulsatile expanding system are presented.