Medical robots are superior to freehand manipulation if an accurate, precise, and time-efficient implementation of a preplanned intervention is required. In the first part of this contribution a new modular minirobot for automatic ultrasound-based bone cement detection followed by subsequent cement milling in revision total hip replacement is presented. A minirobot integrated ultrasound module eliminates the need for external position tracking (e.g. by an optical system) as well as patient registration since the scanned contours can be directly provided within the robot's coordinate system. Further, the modular minirobot concept allows kinematics, workspace, and mechanical parameters to be easily adapted to the requirements of related or even new surgical applications. In the experimental part, the impact of ultrasound module integration on the implementation of optimized scanning strategies is investigated and evaluated in a laboratory set-up. As wave mode conversion and refraction artefacts due to angular sound incidence influence the detection accuracy, the transducer alignment can be optimized with respect to the number of degrees of freedom (DOFs) provided by the minirobot. A model-based scanning approach using two degrees of freedom (2DOFs), three degrees of freedom (3DOFs), and four degrees of freedom (4DOFs) respectively is presented. For automated scanning path calculation, a 2DOF distal-proximal prescan has been performed to estimate the principal components of the cement cavity's geometry using either a model-based or a statistical approach. In a cadaver study, the model-based approach consistently outperformed the statistical approach. The 3DOFs and 4DOFs scanning strategies yielded a significantly higher scanning accuracy if compared with the 2DOFs approach whereas the 3DOFs approach represents a trade-off between system complexity and detection accuracy.

Currently, there are only a small number of robotic systems used in various surgical fields. As modified industrial robot systems have shown significant limitations in the past, specialized kinematic solutions have been proposed for specific surgical applications. The majority of these systems are designed for specific applications in only a limited number of cases. The acquisition and operating costs are high, hindering the dissemination and broad clinical application of such systems. To address this problem, a modular mini-robot system is proposed, which can be easily adapted to different application-specific requirements. Therefore, the requirements of different applications have been categorized and clustered to a standardized requirement profile. Next, a modular robot based on a hybrid kinematic module structure has been developed. This concept has been implemented and tested in in vitro studies for different applications, such as revision total hip replacement and unicondylar knee arthroplasty. User-orientated tests of the intraoperative handling, as well as accuracy tests, proved the feasibility of the concept.

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