Smart Impedance Controlled Osteotomy Instrumentation

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Osteotomy, the cutting of bones, is a standard procedure in different surgical disciplines. Efficient cutting of the bone and a good protection of close sensitive soft tissue structures is crucial. Two procedures of high relevance in this area are craniotomy (opening of the skull, around 66000 cases, Germany/2008) and resternotomy (reopening of the chest, approximately 13500 cases, Germany/2008). In both cases a bicortical bone is cut, while underlying sensitive and live critical soft tissue structures (e.g. central nervous system, heart, blood vessels) have to be protected. During craniotomy in 30 % of all cases a tear of the dura mater occurs, which leads to a significant increase in operation time and a worse result for the patient. Moreover, injuries of the retrosternal structures during repeated sternotomy (resternotomy) are responsible for a high mortality which even increases with every reoperation performed.To support the surgeon during osteotomies many active hand held instruments and robotic systems were developed. These semiautomatic instruments or automatic robots process the bone on the basis of pre- or intraoperative acquired imaging data (e.g. CT, ultrasound). The disadvantages of these approaches are the many additional procedures necessary and the complex integration into the medical standard workflow. In case of a hand guided instrument, which controls one or two degrees of freedom automatically only on the basis in process acquired data, this is not the case. One of the applicants was able to show the general feasibility for a light based in process measurement and control approach. Due to the light based measurements and the current control strategy the system is very sensitive to failures and disturbances. However, in collaborative work, the two applicants were able to show the potential of bio impedance spectroscopy (BIS) for the automatic in process control of a surgical robot system for the bone cement removal in revision total hip replacement.In the proposed research project the potential of a hand guided, sensor integrated and controlled, intelligent instrument for resternotomy and craniotomy is investigated. For this reason, the optimal integration of BIS into a sensor controlled instrument has to be analyzed and after that its use is verified in-vitro. Central challenges are the online BIS measurement during the cutting process and the active fault tolerant control of the instrument under involvement of the surgeon. Object of research is also the combination of the high technical precision (knowledge based, sensor controlled process control) of the intelligent instrument with the high cognitive abilities of the surgeon for the control of the overall process. This signifies that in complement to the complex measurement process, the approaches for active fault tolerant control particularly with regard to a synergistic man-machine interaction have to be implemented into a demonstrator system and finally evaluated.