David Fürst

Transpedicular Approach on a Novel Spine Simulator: A Validation Study

OBJECTIVE The popularity of simulation in the medical field has increased dramatically over the last decades. However, the majority of studies focused on laparoscopic or other endoscopic procedures. In this study, participants performed an image-guided surgery task on a novel spine simulator. Face, content, construct, and concurrent validity were examined. DESIGN A surgical access through both pedicles (transpedicular) into the vertebral body of artificial L3 vertebrae was performed. Questionnaires, a simulation-based performance score, and a specialist rating were used to evaluate the various forms of validity. SETTING Klinikum Wels-Grieskirchen, Wels, Austria; tertiary hospital PARTICIPANTS: According to their expertise in image-guided surgery and pedicle tool insertions, 43 participants were subdivided into 3 groups: 22 novices, 12 intermediates, and 9 experts. RESULTS Of the novice group, the vast majorities were impressed with the attractiveness and the general appearance of the simulator. The majority of intermediates (92%) and experts (89%) would recommend the simulator to others. According to a simulation-based performance score, experts performed significantly better than novices (p = 0.001, d = 1.52) and intermediates (p = 0.01, d = 1.26). The association between the simulation-based performance score and the specialist rating was strong (R = 0.86, p < 0.01). CONCLUSIONS The novel spine simulator provides an applicable tool for the training of image-guided surgery skills in a realistic design. Its simulation-based assessment score classifies different levels of expertise accurately.

Novel bone surrogates for cranial surgery training

Parietal graft lifts are trained on human or animal specimens or are directly performed on patients without extensive training. In order to prevent harm to the patient resulting from fast rotating machinery tools, the surgeon needs to apply appropriate forces. Realistic haptics are essential to identify the varying parietal bone layers and to avoid a penetration of the brain. This however, requires experience and training. Therefore, in this study, bone surrogate materials were evaluated with the aim to provide an anatomically correct artificial skull cap with realistic haptic feedback for graft lift training procedures. Polyurethane composites made of calcium carbonate and calcium phosphate were developed and were used to create customized bone surrogates, imitating both cancellous and cortical bone. Mechanical properties of these surrogates were validated for drilling, milling and sawing by comparison with human parietal bones. For that, surgical tool tips were automatically inserted into artificial and human bones in a customized test bench and the maximum axial insertion forces were analyzed. Axial tool insertion measurements in human parietal bones resulted in mean maximum forces of 1.8±0.5N for drilling, 1.7±0.3N for milling and 0.9±0.1N for sawing. Calcium carbonate-based materials achieved higher forces than the human bone for drilling and milling, and lower forces for sawing. The calcium phosphate-based bone surrogates showed comparable axial insertions forces for all investigated tools and were identified as a suitable surrogate for drilling (p=0.87 and 0.41), milling (p=0.92 and 0.63) and sawing (p=0.11 and 0.76) of the cortical layer and the cancellous bone, respectively. In conclusion, our findings suggest, that a suitable material composition for artificial parietal bones has been identified, mimicking the properties of human bone during surgical machinery procedures. Thus, these materials are suitable for surgical training and education in simulator training.

Characterization of synthetic foam structures used to manufacture artificial vertebral trabecular bone

Artificial materials reflecting the mechanical properties of human bone are essential for valid and reliable implant testing and design. They also are of great benefit for realistic simulation of surgical procedures. The objective of this study was therefore to characterize two groups of self-developed synthetic foam structures by static compressive testing and by microcomputed tomography. Two mineral fillers and varying amounts of a blowing agent were used to create different expansion behavior of the synthetic open-cell foams. The resulting compressive and morphometric properties thus differed within and also slightly between both groups. Apart from the structural anisotropy, the compressive and morphometric properties of the synthetic foam materials were shown to mirror the respective characteristics of human vertebral trabecular bone in good approximation. In conclusion, the artificial materials created can be used to manufacture valid synthetic bones for surgical training. Further, they provide novel possibilities for studying the relationship between trabecular bone microstructure and biomechanical properties.

Characterization of polyurethane-based synthetic vertebrae for spinal cement augmentation training

Vertebral augmentation techniques are used to stabilize impacted vertebrae. To minimize intraoperative risks, a solid education of surgeons is desirable. Thus, to improve education of surgeons as well as patient safety, the development of a high-fidelity simulator for the surgical training of cement augmentation techniques was initiated. The integrated synthetic vertebrae should be able to provide realistic haptics during all procedural steps. Synthetic vertebrae were developed, tested and validated with reference to human vertebrae. As a further reference, commercially available vertebrae surrogates for orthopedic testing were investigated. To validate the new synthetic vertebrae, characteristic mechanical parameters for tool insertion, balloon dilation pressure and volume were analyzed. Fluoroscopy images were taken to evaluate the bone cement distribution. Based on the measurement results, one type of synthetic vertebrae was able to reflect the characteristic parameters in comparison to human vertebrae. The different tool insertion forces (19.7 ± 4.1, 13.1 ± 0.9 N, 1.5 ± 0.2 N) of the human reference were reflected by one bone surrogate (11.9 ± 9.8, 24.3 ± 3.9 N, 2.4 ± 1.0 N, respectively). The balloon dilation pressure (13.0 ± 2.4 bar), volume (2.3 ± 1.5 ml) of the synthetic vertebrae were in good accordance with the human reference (10.7 ± 3.4 bar, 3.1 ± 1.1 ml). Cement application forces were also in good accordance whereas the cement distribution couldn’t be reproduced accurately. Synthetic vertebrae were developed that delivered authentic haptics during transpedicular instrument insertion, balloon tamp dilation and bone cement application. The validated vertebra model will be used within a hybrid simulator for minimally invasive spine surgery to educate and train surgeons.HighlightsAnatomically realistic open-celled vertebrae based on polyurethane and calcium-based mineral fillers were developed.Spine surgery specific testing of human and synthetic vertebrae were conducted.The examined tool insertion forces and balloon tamp dilation pressures of artificial vertebrae were highly comparable to human ones.Open-celled artificial vertebrae enabled a realistic bone cement distribution.Realistic haptic performance and behavior of two composite materials confirmed their suitability for training in the field of spine surgery.

Characterization of an artificial skull cap for cranio-maxillofacial surgery training

Cranial grafts are favored to reconstruct skeletal defects because of their reduced resorption and their histocompatibility. Training possibilities for novice surgeons include the “learning by doing” on the patient, specimens or simulators. Although the acceptance of simulators is growing, the major drawback is the lack of validated bone models. The aim of this study was to create and validate a realistic skull cap model and to show superiority compared to a commercially available skull model. Characteristic forces during machinery procedures were recorded and thickness parameters from the bony layers were obtained. The thickness values of the bone layers of the developed parietal bone were comparable to the human ones. Differences between drilling and sawing forces of human and artificial bones were not detected using statistical analysis. In contrast the parameters of the commercially available skull model were significantly different. However, as a result, a model-based simulator for tabula externa graft lift training, consisting of a brain, skull bone cap and covering soft tissues was created. This simulator enables the training of all procedural steps of a “split thickness graft lift”. In conclusion, an artificial skull cap suitable for parietal graft lift training was manufactured and validated against human parietal bones.HighlightsAxial tool insertion forces were identified as suitable parameter to validate haptics of artificial bone materials compared to human bone.Poylurethane edited with mineral fillers and blowing agents can realisitcally mimic skull bones.μCT images prove the realistic thickness of all bone layers.Realistic haptic performance of artificial skull caps confirmed their suitability for training in the field of cranio-maxillofacial surgery.

Development of parietal bone surrogates for parietal graft lift training

Abstract Currently the surgical training of parietal bone graft techniques is performed on patients or specimens. Commercially available bone models do not deliver realistic haptic feedback. Thus customized parietal skull surrogates were developed for surgical training purposes. Two human parietal bones were used as reference. Based on the measurement of insertion forces of drilling, milling and saw procedures suitable material compositions for molding cortical and cancellous calvarial layers were found. Artificial skull caps were manufactured and tested. Additionally microtomograpy images of human and artificial parietal bones were performed to analyze outer table and diploe thicknesses. Significant differences between human and artificial skulls were not detected with the mechanical procedures tested. Highly significant differences were found for the diploe thickness values. In conclusion, an artificial bone has been created, mimicking the properties of human parietal bone thus being suitable for tabula externa graft lift training.