Configuration optimization and experimental accuracy evaluation of a bone-attached, parallel robot for skull surgery

Purpose Minimally invasive cochlear implantation is a novel surgical technique which requires highly accurate guidance of a drilling tool along a trajectory from the mastoid surface toward the basal turn of the cochlea. The authors propose a passive, reconfigurable, parallel robot which can be directly attached to bone anchors implanted in a patient's skull, avoiding the need for surgical tracking systems. Prior to clinical trials, methods are necessary to patient specifically optimize the configuration of the mechanism with respect to accuracy and stability. Furthermore, the achievable accuracy has to be determined experimentally. Methods A comprehensive error model of the proposed mechanism is established, taking into account all relevant error sources identified in previous studies. Two optimization criteria to exploit the given task redundancy and reconfigurability of the passive robot are derived from the model. The achievable accuracy of the optimized robot configurations is first estimated with the help of a Monte Carlo simulation approach and finally evaluated in drilling experiments using synthetic temporal bone specimen. Results Experimental results demonstrate that the bone-attached mechanism exhibits a mean targeting accuracy of (0.36 +/- 0.12) mm under realistic conditions. A systematic targeting error is observed, which indicates that accurate identification of the passive robot's kinematic parameters could further reduce deviations from planned drill trajectories. Conclusion The accuracy of the proposed mechanism demonstrates its suitability for minimally invasive cochlear implantation. Future work will focus on further evaluation experiments on temporal bone specimen.