Robot Assisted Registration for Total Knee Replacement

Objective: Registration is a critical step, which links the planning and execution phases of most CAS applications. In this procedure the geometric relationships between the patient’s anatomy, the models used for planning and the robotic or sensorized tools employed intrasurgically, are calculated. The registration scheme described in this paper, based on enhanced ICP algorithm, doesn’t need any marker implant, thus reducing surgical invasiveness. Points on the bone surface are sampled by the robot which in turn, directs the surgical tool, thus eliminates additional coordinate transformation and increases operation accuracy. Materials and Methods: The registration technique was tested on an RSPR six degrees-of-freedom parallel robot specifically designed for medical applications. The six axis force sensor attached to the robot’s moving platform, enables fast and accurate acquisition of positions and bone surface normals at sampled points. Results: Sampling with a robot probe was shown to be accurate, fast and easy to perform. The robot alone does most of the registration work, leaving surgeon’s hands free. The whole procedure takes about 4 minutes. Conclusions: The simplicity and accuracy of the proposed registration appears to be sufficient for orthopaedic surgical applications. Robotic registration makes the flawless connection between the preoperative planning and robotic assistance during surgery.