Thorsten Tjardes

Image-guided spine surgery: state of the art and future directions.

Navigation technology is a widely available tool in spine surgery and has become a part of clinical routine in many centers. The issue of where and when navigation technology should be used is still an issue of debate. It is the aim of this study to give an overview on the current knowledge concerning the technical capabilities of image-guided approaches and to discuss possible future directions of research and implementation of this technique. Based on a Medline search total of 1,462 publications published until October 2008 were retrieved. The abstracts were scanned manually for relevance to the topics of navigated spine surgery in the cervical spine, the thoracic spine, the lumbar spine, as well as ventral spine surgery, radiation exposure, tumor surgery and cost-effectivity in navigated spine surgery. Papers not contributing to these subjects were deleted resulting in 276 papers that were included in the analysis. Image-guided approaches have been investigated and partially implemented into clinical routine in virtually any field of spine surgery. However, the data available is mostly limited to small clinical series, case reports or retrospective studies. Only two RCTs and one metaanalysis have been retrieved. Concerning the most popular application of image-guided approaches, pedicle screw insertion, the evidence of clinical benefit in the most critical areas, e.g. the thoracic spine, is still lacking. In many other areas of spine surgery, e.g. ventral spine surgery or tumor surgery, image-guided approaches are still in an experimental stage. The technical development of image-guided techniques has reached a high level as the accuracies that can be achieved technically meet the anatomical demands. However, there is evidence that the interaction between the surgeon (‘human factor’) and the navigation system is a source of inaccuracy. It is concluded that more effort needs to be spend to understand this interaction.

Drivers of acute coagulopathy after severe trauma: a multivariate analysis of 1987 patients

Objective The role of acute coagulopathy after severe trauma as a major contributor to exsanguination and death has recently gained increasing appreciation, but the causes and mechanisms are not fully understood. This study was conducted to assess the risk factors associated with acute traumatic coagulopathy together with quantitative estimates of their importance. Methods Using the multicentre Trauma Registry of the German Society for Trauma Surgery, adult trauma patients with an Injury Severity Score ≥16 were retrospectively analysed for independent risk factors of acute traumatic coagulopathy on arrival at the emergency department (ED) by multivariate stepwise logistic regression analysis. Coagulopathy was defined as prothrombin time test (Quicks value) <70% and/or platelets <100 000/μl. Results A total of 1987 patients was eligible for further analysis. Independent risk factors for acute traumatic coagulopathy calculated by multivariate analysis were the Injury Severity Score, abdomen Abbreviated Injury Scale score, base excess, body temperature ≤35°C, presence of shock at the scene and/or in the ED (defined as systolic blood pressure ≤90 mm Hg), prehospital intravenous colloid:crystalloid ratio ≥1:2 and amount of prehospital intravenous fluids ≥3000 ml. Conclusions The risk factors from multivariate analysis correspond to the current understanding that coagulopathy is influenced by several clinical key factors; for example, an ongoing state of shock (at the scene and in the ED) was associated with a threefold increased risk of developing coagulopathy. When adjusted for all factors including the amount of prehospital intravenous fluids, a high colloid:crystalloid ratio was still associated with coagulopathy on admission to the ED. The recognition, prevention and management of the mechanisms and risk factors of coagulopathy aggravating haemorrhage after trauma are critical in the treatment of the severely injured patient.

Computer Assisted Percutaneous Placement of Augmented Iliosacral Screws : A Reasonable Alternative to Sacroplasty

Study Design. A technical report of fluoroscopy guided placement of augmented iliosacral screws in osteoporotic insufficiency fractures of the sacrum. Objective. To describe a combined approach of navigated iliosacral screw placement and screw augmentation as an option for osteosynthesis of sacral insufficiency fractures in the elderly. Summary of Background Data. The incidence of sacral insufficiency fractures is increasing. Outcome of conservative treatment is inconsistent. Recently sacroplasty is propagated as an interventional therapy but the long-term outcome is still unknown. Evidence from finite element models suggests that stabilization of the sacrum achieved by sacroplasty is insufficient to restore the weight bearing capacity of the sacrum permanently. Methods. We suggest a minimally invasive fluoroscopically navigated iliosacral screw osteosynthesis with cement augmentation of the screws for treatment of insufficiency fractures of the sacrum. Results. The procedure, especially fluoroscopic visualization and navigation of the osteoporotic sacrum is technically feasible. A total radiograph time of 7,4 minutes, including image acquisition for navigation and fluoroscopic control of cement injection, is acceptable and can be expected to be significantly reduced with repeated applications of the procedure. The patient presented in the report was discharged to rehabilitation soon after the operation. An assistive device (delta wheel) is only needed for longer walking distances. Pain was reduced drastically immediately after surgery. Conclusion. In general, fractures are treated by reduction and fixation to restore the biomechanical function of the injured bone. These principles should be applied to elderly patients with osteoporotic fractures as well. The technique reported here is adapted to the special demands of the elderly patient, i.e., minimally invasive, support of the weakened bone by cement augmentation, bone protective screw positioning and safety due to navigation support.

Precision of Tunnel Positioning in Navigated Anterior Cruciate Ligament Reconstruction

PURPOSE The aim of this study was to validate the precision of navigated tunnel positioning using a fluoroscopy-based computer-assisted technique. METHODS Ten human cadaveric knees were operated on under operating room conditions. After resection of the anterior cruciate ligament, referenced fluoroscopic images were acquired to plan the tunnel positions according to established radiologic measurement methods. Afterward, femoral and tibial K-wires were placed by use of navigated drill guides without arthroscopic control. Deviations between the planned and actually drilled tunnel positions at the joint level were analyzed by use of both navigated and radiologic assessment methods. RESULTS Navigated analysis between planned and actually drilled tunnel position showed mean deviations of 0.4 mm (range, 0 to 1 mm; SD, 0.52 mm) at the femur and 0.5 mm (range, 0 to 1 mm; SD, 0.5 mm) at the tibia. The radiologic analysis showed mean deviations for the femoral tunnel of 0.83 mm for the depth (range, 0 to 1.46 mm; SD, 0.46 mm) and 0.54 mm for the height (range, 0 to 1.08 mm; SD, 0.41 mm). At the tibia, deviation of 0.74 mm (range, 0 to 1.2 mm; SD, 0.46 mm) was found. CONCLUSIONS The fluoroscopy-based navigation system used in this study allows for precise tunnel positioning with deviations of 1 mm or less. CLINICAL RELEVANCE This technique provides accurate tunnel placement in anterior cruciate ligament surgery.

Bacterial contamination of open fractures - pathogens, antibiotic resistances and therapeutic regimes in four hospitals of the trauma network Cologne, Germany.

INTRODUCTION The bacterial contamination of soft tissues and bone in open fractures leads to an infection rate of up to 50%. Pathogens and their resistance against therapeutic agents change with time and vary in different regions. In this work, our aims were to characterize the bacterial spectrum present in open fractures, analyze the bacterial resistance to antibiotic agents and question the EAST guideline recommendations for antibiotic prophylaxis after open fractures in a German Trauma Network. MATERIALS AND METHODS We conducted a retrospective cohort study and included all patients with open fractures from 1(st) of January 2011 until the 31(st) of December 2014 in four hospitals of the trauma network cologne. Soft tissue damage was classified according to the Gustilo Anderson classification. RESULTS We included 123 patients. Forty-five injuries (37%) were classified I°, 45 (37%) as II° and 33 (27%) as III°. Lower leg (34%) was the most commonly injured location. An antibiotic prophylaxis was administered to 109 patients (89%). In 107 of them (98%) a cephalosporin or cephalosporin combination was given. In 35 of the patients (28%), microbiological samples were taken of the fracture site. Wound cultures were positive in 21 patients (60%). Fifty percent of the bacterial detections occurred in III° fractures. Coagulase negative Staphylococci (COST) were the most frequent pathogens. In II° open fractures one gram-negative strain was isolated. Fewest resistances were seen against quinolones and co-trimoxazole. DISCUSSION The recommended EAST guideline prophylaxis would have covered all but one bacterium (97% of positive cultures). One Escherichia coli was found in a II° open fracture and would have been missed. One of the isolated Staphylococci epidermidis and an Enterococcus faecium were resistant against gentamycin and first- and second-generation-cephalosporins which were used as prophylaxis frequently. However, a regional adaption of the EAST guidelines seems not justified due to the rather low number of cases in our study. CONCLUSION The EAST guideline seems to be adequate in a high percentage of cases (97%) in the setting of the trauma network cologne. Further research should be guided at identification of initial open fracture pathogens to improve the efficiency of antibiotic prophylaxis.

Extension injury of the thoracic spine with rupture of the oesophagus and successful conservative therapy of concomitant mediastinitis

The case of an upper oesophageal perforation as a concomitant injury of an isolated fracture of the upper thoracic spine without neurological compromise has not been described so far. A Case report and review of the literature is presented here. Concomitant oesophageal perforations carry a high risk of being missed initially. CT alone can visualize the subtle indirect signs like peri-oesophageal air. The literature revealed that only peri-oesophageal air might be a valid indicator of oesophageal injury. There are no systematic data on thoracic spine fractures with concomitant oesophageal perforations. Mediastinitis secondary to oesophageal perforation might be treated conservatively with endoscopic stent placement rather than surgically. As the radiological signs of concomitant soft tissue injury, like oesophageal perforations, in fractures of the upper thoracic spine are subtle and easily missed initially only anticipation of concomitant injuries by the treating physician based on the trauma mechanism ensures a timely diagnosis.

An automated workflow for the biomechanical simulation of a tibia with implant using computed tomography and the finite element method

In this study, a fully automated workflow is presented for the biomechanical simulation of bone-implant systems using the example of a fractured tibia. The workflow is based on routinely acquired tomographic data and consists of an automatic segmentation and material assignment, followed by a mesh generation step and, finally, a mechanical simulation using the finite element method (FEM). Because of the high computational costs of the FEM simulations, an adaptive mesh refinement scheme was developed that limits the highest resolution to materials that can take large amounts of mechanical stress. The scheme was analyzed and it was shown that it has no relevant impact on the simulation precision. Thus, a fully automatic, reliable and computationally feasible method to simulate mechanical properties of bone-implant systems was presented, which can be used for numerous applications, ranging from the design of patient-specific implants to surgery preparation and post-surgery implant verification.

An optimization algorithm for individualized biomechanical analysis and simulation of tibia fractures.

An algorithmic strategy to determine the minimal fusion area of a tibia pseudarthrosis to achieve mechanical stability is presented. For this purpose, a workflow capable for implementation into clinical routine workup of tibia pseudarthrosis was developed using visual computing algorithms for image segmentation, that is a coarsening protocol to reduce computational effort resulting in an individualized volume-mesh based on computed tomography data. An algorithm detecting the minimal amount of fracture union necessary to allow physiological loading without subjecting the implant to stresses and strains that might result in implant failure is developed. The feasibility of the algorithm in terms of computational effort is demonstrated. Numerical finite element simulations show that the minimal fusion area of a tibia pseudarthrosis can be less than 90% of the full circumferential area given a defined maximal von Mises stress in the implant of 80% of the total stress arising in a complete pseudarthrosis of the tibia.

Less than full circumferential fusion of a tibial nonunion is sufficient to achieve mechanically valid fusion - Proof of concept using a finite element modeling approach

BackgroundAlthough minimally invasive approaches are widely used in many areas of orthopedic surgery nonunion therapy remains a domain of open surgery. Some attempts have been made to introduce minimally invasive procedures into nonunion therapy. However, these proof of concept studies showed fusion rates comparable to open approaches never gaining wider acceptance in the clinical community. We hypothesize that knowledge of mechanically relevant regions of a nonunion might reduce the complexity of percutaneous procedures, especially in complex fracture patterns, and further reduce the amount of cancellous bone that needs to be transplanted. The aim of this investigation is to provide a proof of concept concerning the hypothesis that mechanically stable fusion of a nonunion can be achieved with less than full circumferential fusion.MethodsCT data of an artificial tibia with a complex fracture pattern and anatomical LCP are converted into a finite element mesh. The nonunion area is segmented. The finite element mesh is assigned mechanical properties according to data from the literature. An optimization algorithm is developed that reduces the number of voxels in the non union area until the scaled von Mises stress in the implant reaches 20% of the maximum stress in the implant/bone system that occurs with no fusion in the nonunion area at all.ResultsAfter six iterations of the optimization algorithm the number of voxels in the nonunion area is reduced by 96.4%, i.e. only 3.6% of voxels in the non union area are relevant for load transfer such that the von Mises stress in the implant/bone system does not exceed 20% of the maximal scaled von Mises stress occurring in the system with no fusion in the non union area at all.ConclusionsThe hypothesis that less than full circumferential fusion is necessary for mechanical stability of a nonunion is confirmed. As the model provides only qualitative information the observed reduction of fusion area may not be taken literally but needs to be calibrated in future experiments. However this proof of concept provides the mechanical foundation for further development of minimally invasive approaches to delayed union and nonunion therapy.