M. de la Fuente

Myocardial effects of local shock wave therapy in a Langendorff model.

OBJECTIVE Applying shock waves to the heart has been reported to stimulate the heart and alter cardiac function. We hypothesized that shock waves could be used to diagnose regional viability. METHOD We used a Langendorff model to investigate the acute effects of shock waves at different energy levels and times related to systole, cycle duration and myocardial function. RESULTS We found only a small time window to use shock waves. Myocardial fibrillation or extrasystolic beats will occur if the shock wave is placed more than 15 ms before or 30 ms after the onset of systole. Increased contractility and augmented relaxation were observed after the second beat, and these effects decreased after prolonging the shock wave delay from 15 ms before to 30 ms after the onset of systole. An energy dependency could be found only after short delays (-15 ms). The involved processes might include post-extrasystolic potentiation and simultaneous pacing. CONCLUSION In summary, we found that low-energy shock waves can be a useful tool to stimulate the myocardium at a distance and influence function.

Evaluation of a fluoroscopy-based navigation system enabling a virtual radiation-free preview of X-ray images for placement of cannulated hip screws. A cadaver study

Accurate placement of cannulated screws is essential to ensure fixation of medial femoral neck fractures. The conventional technique may require multiple guide wire passes, and relies heavily on fluoroscopy. A computer-assisted planning and navigation system based on 2D fluoroscopy for guide wire placement in the femoral neck has been developed to improve screw placement. The planning process was supported by a tool that enables a virtual radiation-free preview of X-ray images. This is called “zero-dose C-arm navigation”. For the evaluation of the system, six formalin-fixed cadaveric full-body specimens (12 femurs) were used. The evaluation demonstrated the feasibility of fluoroscopically navigated guide wire and implant placement. Use of the novel system resulted in a significant reduction in the number of fluoroscopic images and drilling attempts while achieving optimized accuracy by attaining better screw parallelism and enlarged neck-width coverage. Operation time was significantly longer in the navigation assisted group. The system has yielded promising initial results; however, additional studies using fractured bone models and with extension of the navigation process to track two bone fragments must be performed before integration of this navigation system into the clinical workflow is possible, and these studies should focus on reducing the operation time.

Determination of the Mechanical Leg Axis Using a Force-Torque Sensor

The correct determination of the mechanical leg axis (so called Mikulicz-Line) is cruicial step for the correct alignment of prosthesis components in Total Knee Arthroplasty (TKA). The newly developed “genALIGN”-system uses a force-torque sensor to directly measure the torques induced by a deviation from the mechanical axis. During surgery, the device is fixed to the knee center and a force is applied in the approximate direction of the hip center. An unstable system is created which can only reach equilibrium, when both the device and the mechanical leg axis are coaxial, i.e. the device points exactly in direction of the hip center. The result can be easily fixed and the bone cuts can be performed using an attachable cutting jig. To account for the leg’s weight, the sensor is adjusted to zero before starting the actual measurement.

In.nrw Hyther: Electromagnetically navigated in situ fenestration of aortic stent grafts

The endovascular repair of aortic aneurysms overlapping regions with side branches (e.g. renal arteries) is a remaining challenge, as sufficient fixation of the stent graft with preservation of the blood flow to abdominal organs is hindered considerably, frequently necessitating open surgery or complex debranching operations followed by graft implantation. In this abstract we present a concept and phantom study for in-situ fenestration of aortic stent grafts using an electromagnetically guided catheter/guidewire system to allow for endovascular repair of large AAA.

Accuracy of Optical Localizers for Computer Aided Surgery

The localization of surgical tools and the patient’s reference coordinate system in three to six degrees of freedom is one of the key technologies in computer aided surgery. Several tracking methods are available, among which optical tracking is the most widespread in clinical use. Optical tracking technology has well proven to be a reliable method for intra-operative position and orientation acquisition for many clinical applications. However, the accuracy of these localizers is still a topic of discussion. In this paper, the accuracy of three optical localizer systems, the NDI Polaris P4, NDI Polaris Spectra (active and passive mode) and the Stryker Navigation System II Camera, is assessed and critically compared. Static tests revealed that only the Polaris P4 shows a significant warm up behavior with a significant shift of accuracy within 42 minutes after switching it on. Furthermore, the intrinsic localizer accuracy was determined for single markers as well as for typical tools using a volumetric measurement protocol on a coordinate measurement machine. To determine the relative distance error within the measurement volume, the Length Measurement Error (LME) was determined at 35 test lengths. The two active localizer systems, the Stryker Navigation System II camera and the Polaris Spectra (active mode), showed the best results with a trueness of 0.058±0.033mm and 0.089±0.061 mm, respectively (mean±std. dev.). The Polaris Spectra (passive mode) showed a trueness of 0.170±0.090mm and the Polaris P4 showed the lowest trueness with 0.272±0.394mm and a higher number of outliers than all the other cameras.

Evaluation of a new computer-assisted surgical planning and navigation system based on two-dimensional fluoroscopy for insertion of a proximal femoral nail: an experimental study.

Pertrochanteric femoral fractures are common and intramedullary nailing is an accepted method for their surgical treatment. Accurate placement of the implant is essential to ensure fixation. The conventional technique can require multiple guide wire passes, and relies heavily on fluoroscopy. A computer-assisted planning and navigation system based on two-dimensional fluoroscopy for guide wire placement in the femoral neck has been developed, in order to perform intramedullary pertrochanteric fracture fixation using the proximal femoral nail (PFNA®). The planning process was supported by a ‘zero-dose C-arm navigation’ system. The PFNA was inserted into 12, intact, femoral sawbones guided by the computer-based navigation, and into 12, intact, femoral sawbones using a conventional fluoroscopic-assisted technique. Guide wire and subsequent blade placement in the femoral neck was evaluated. The computer-assisted technique achieved a significant decrease in the number of required fluoroscopic images and in the number of guide wire passes. The obtained average blade placement accuracy in the femoral neck was equivalent to the conventional technique. The operation time was significantly longer in the navigation-assisted group. The addition of computer-assisted planning and surgical guidance to the intramedullary nailing of pertrochanteric femoral fractures offers a number of clinical benefits based on the results of this sawbone study. Further studies including fractured sawbones and cadaver models with extension of the navigation process to all steps of PFNA introduction and with the goal of reducing operation time are indispensable before integration of this navigation system into clinical practice.