Konzeption und Aufbau eines Systems zur navigierten und roboter-assistierten Laserosteotomie mit spektroskopischer Rückkopplung

Osteotomy, the cutting of bones, is a necessary and important step in many surgical procedures. Today it is common practice in surgery to use mechanical tools like oscillating saws, rotating burrs or chisels. These traditional instruments hold some disadvantages like increasing temperature, friction injury, and other microtraumata in the bony tissues. In addition, the handling of these tools is somewhat sensitive to the technical skills of the surgeon. Developing such skills can take long training with the instruments and
much hands-on experience to accomplish complicated geometries.
Some years ago a research group of the Institute of Laser Medicine at the University of Duesseldorf developed a new technique to cut bones by using a laser, called laser osteotomy, as an alternative to existing osteotomy techniques. They established the basis of this technique and proved in several studies that it is possible to make precise contact-free cuts while conserving bony tissue and producing little heat artifact. This laser system executes several cutting geometries and adapts to the surgical procedure by using a laser scanner. The research group used a CO2-Laser at a wavelength of 10,6µm.
Its laser beam can be applied in an array of about 70x70mm2 on
at surfaces. If the laser is needed to cut deeper and larger areas, it has to be positioned by hand in its current state. This manually adjustment will lead to inaccuracies in most cases because the focal point of the laser system has to be repositioned mechanically by hand and by sight with increasing depth of the cut. Additionally, an ability to set parameters to automatically stop the laser cut in case of undesired cuts for example when it reaches the border of a defined area is still missing.
In this dissertation, the research project ESCURAL (experimental setup for a computed robot assisted laserosteotomy) is presented. The goal is to provide surgeons with an assistance system to cut bones with more precision and less tissue damage in the surgical field. The experimental procedure involves positioning and locking of the laser scanner over the field of ablation by a robotic system. With this set up, longer and combined cuts on curved surfaces with an adjustment of the focal point can be realized with technical precision. The surgeon plans the cut with the help of an optical tracking device and a
choice of predetermined trajectories. Out of this planned geometry of the cut, a trajectory is calculated and the robot and the laser get actuated. The robot is supervised in its position and orientation by the optical tracking system. During the process of the laser cut plasma arises above the place of ablation. By analysis of the spectrum of the plasma, information is gathered about whether the laser is cutting bone, the bone is already cut through, or the surrounding soft tissue is being affected. An immediate automatic shut off can be programmed to stop the laser if the spectrum analysis indicates that soft
tissue has been reached or the bone is cut through. This way a real-time supervision of the laser cut is achieved. The experimental set up contains all components of the system including robot, tracking system, laser, laser-scanner and the cut supervision program. All of these are supposed to interact and to be controlled by one computer with a graphical user interface.
This system of a robot-assisted laserosteotomy can be successfully applied where exact cuts on bones are necessary because, for example, a common surgical therapy has a significant outcome for the patients’ appearance. Emergency use of ESCURAL would be impractical due to the high amount of instrumentation required and the necessary planning phase in using this equipment. However in medical specialties as Oral and Maxillofacial Surgery, Neurosurgery or Thoracic and Cardiovascular Surgery precise treatment of the bone is required to keep the process of healing as short and comfortable as possible and to lower complication rates.