19.1 The Pathway from Bone Cutting with Mechanical Tools to Lasers

Archaeological findings from the Stone Age show that humans have always used mechanical tools such as saws, scrapers, knives, and drills to perform interventions on the human body [1]. These mechanical principles of cutting and drilling have not changed much since then. The surgical instruments have of course become more precise, more sophisticated, and also sterile, but they all work according to simple mechanical principles. Especially in orthopedic surgery and in all interventions in which bone is removed, relatively large forces and torques occur, which also affect the adjacent tissue. For example, sawing and drilling create movements combined with high friction forces that heat up the surrounding tissue. Also, the surface in the cut interface is affected and the porous bone tissue is mechanically flattened. This seems to impair the blood supply to the cells near the interface. In experiments on minipigs, piezoosteotomes flattened the bone surface in the cut. In comparison, cutting bone with a 2.94 [nm] Er:YAG laser produced an open, porous interface. Subsequently, the researchers observed faster healing of bone cuts in the tissues with laser cuts. This finding led the researchers to the conclusion that the way of cutting bone seems to matter for heading [2]. Other positive aspects of laser osteotomy compared to conventional mechanical osteotomy are reduced vibrations [3], reduced heat influence on adjacent tissues [4], as well as higher precision, narrower cuts, arbitrary cut shapes, and faster bone formation in the healing process [5, 6].

19.2 CARLO^®, the First Robot for Bone Cutting with Laser

The combination of the many advantages of laser osteotomy over conventional osteotomy has led to the development of the world’s first robot for laser osteotomy: CARLO^® (short for “Cold Ablation Robot -guided Laser Osteotome” [7], originally patented as “Computer-Assisted and Robot-guided Laser Osteotome” [8]). CARLO^® was invented by the founders of Advanced Osteotomy Tools (AOT AG, Basel, Switzerland), a spin-off from the University of Basel. The laser osteotome CARLO^® consists of a serial robot and a laser head. The laser head houses the optical components and the nozzles for the irrigating water spray. The robot is basically used as a tool for guiding the laser precisely along the desired cutting paths. Hereby, the movements of the robot are usually pre-planned based on Computed Tomography (CT) data of the respective patient. Registration of the robot, the patient, and the reference CT data set are accomplished via an optoelectronic tracking system.

First studies with CARLO^® in human cadavers have been successfully completed and have confirmed positive results from earlier animal studies. In addition to the high cutting accuracy, robot-assisted laserosteotomes can keep up with conventional surgical methods despite the low cutting speed. While mechanical saws cut fast, reconstruction and osteosynthesis take long due to missing planning, incision inaccuracies, and positioning inaccuracies of the implants. Conversely, robot-assisted laser osteotomy takes longer, but the cut bones can be connected quickly and accurately with their counter parts/implants and reveal little possibilities for relative movement. This is only possible since robot-assisted laserosteotomy enables cut execution exactly as planned due to precise depth control using feedback from an optical coherence tomograph and precise laser guidance by the robot under surveillance of an optoelectronical tracking system. Another important novelty that allows simple and precise assembly of bones/implants and bones after robot-assisted laserosteotomy are free cutting geometries such as sine patterns or dovetail profiles. The cut bone parts and implants fit together like puzzle pieces with their counterparts and have functional stability already during mating [7]. For fixation, if any, only a few additional screws are required. Accordingly, a follow-up operation for removing the screws is shorter or not even required. In 2020, CARLO^® was successfully applied in the first human patients for maxillofacial surgery. At present, only the relatively high initial costs of the first laser osteotome and the large space requirement in the operating room seem to be limiting factors for laser osteotomy with robots.

19.3 The Future of Laser Osteotomy: The MIRACLE Project

Even if it seems that the end of the technological flagpole has been reached with the invention of CARLO^®, there is still a lot more to come. However, the next step in the development of laser osteotomy systems still requires a few more years of work.

Even if it has not been said explicitly until now, laser osteotomy with CARLO^® implies that the surgeon opens up the patient to expose the bone to be cut. To overcome the need of opening up the patient, a new research project at the University of Basel has been initiated in 2015. This project aims at turning laser osteotomy into a minimally-invasive procedure. The surgeon should be able to perform the same surgical procedure as with CARLO^®, however through a one centimeter wide incision. To reach this new milestone in laserosteotomy, a small miracle is required from the current point of view. However, this miracle seems to turn into reality in a few years from now. According to the researchers around the “MIRACLE project” (short for “Minimally Invasive Robot-Assisted Computer-guided LaserosteotomE”) at the Department of Biomedical Engineering (University of Basel, Switzerland), a first functional prototype will be ready in about 3 years from now. Above all, the big challenge in this project is to reduce the size of all components so that the laser can be housed inside a flexible robotic endoscope. At the same time, there should still be room for the actuation of the flexible robotic endoscope itself as well as a working channel, a camera, spray, a suction channel, an optical coherence tomograph (OCT), and other devices for tissue type classification. At the end of surgical procedures with the MIRACLE osteotome, also implants will be introduced into the body in a minimal invasive way to be assembled and fixed like a 3D puzzle. As unsolvable as the task seems, the MIRACLE project can already present first results. The first implants are already distributed via the two spin-offs of the University of Basel “Di Meliora” and “Ad Mirabiles.” Also, the planning software, which is used in the MIRACLE project, is already being used at the University Hospital Basel for diagnosis and patient education in selected departments. The planning software is also being used for training purposes with medical students at the Anatomical Institute of the University of Basel. The intriguing novelty of this planning software is that it can display CT data and Magnetic Resonance Imaging data (MRI data) on virtual reality (VR) glasses in 3D immediately after their acquisition. The virtual patient can then be observed at high resolution and with high repetition rates for both eyes for high immersiveness without cyber-sickness. The user of the VR system can easily interact with the virtual 3D data, can see different tissue types in different colors based on automated segmentation, can scale the 3D model, and inspect it from all sides [9]. Soon, also this planning and medical data visualization software will be available as a commercial product.

In total, four research groups are working on the MIRACLE project. These are the “Bio-Inspired RObots for MEDicine-Lab” (BIROMED-Lab) under the lead of Prof. Dr. Georg Rauter, the “Biomedical Laser and Optics Group” (BLOG) under the lead of Prof. Dr. Azhar Zam, the “Planning and Navigation Group” at the Center for Image Analysis and Navigation (CIAN) under the lead of Prof. Dr. Philippe Cattin, and the “Smart Implants Group” at the “Hightech Forschungszentrum” (HFZ) under the lead of Prof. Dr. med. Dr. med. dent. Dr. hc Hans-Florian Zeilhofer. All four groups are located in one building at the Department of Biomedical Engineering of University of Basel. The close vicinity to each other enables short ways to exchange ideas which is one of the most important factors for successful interdisciplinary research.

19.4 The First Application Areas for the MIRACLE Osteotome

At present, the first clinical application is focused on the half-sided replacement of knee joints (unicondylar knee arthroplasty). This first application should become a benchmark for the MIRACLE osteotome since the knee joint is one of the bones of largest thickness in the human (about 5 [cm]). The goal is to demonstrate that the MIRACLE osteotome can easily cut the knee joint and thus any other bone in the body. However, there are also other areas of application, such as access to the brain without concussion through mechanical manipulation. Also interventions on the spine that are particularly gentle for the spinal cord and the intervertebral discs are foreseen (see Fig. 19.1). Similar to interventions with the CARLO^®, interventions using the MIRACLE osteotome will start with an initial planning phase based on each patient’s CT data or MRI data. In the operating room, the surgeon first guides the robotic endoscope manually to the point of entry into the body. The surgeon can then control the robotic MIRACLE osteotome via a robotic master device (a robotic device that allows teleoperation procedures and provides haptic feedback). The movement of the flexible robotic MIRACLE osteotome inside the patient’s body will be visualized in real-time by augmented reality glasses since it will be difficult for the surgeon to imagine how the flexible endoscope is shaped inside the patient’s body. Once the surgeon has moved the MIRACLE osteotome to the target site, it “attaches” itself to the bone. After successful attachment to the bone, laserosteotomy will be initiated. Since bone tissue retains its shape between the planning and the surgical procedure, the laserosteotomy can be performed autonomously by the robot under supervision of the surgeon.

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