12th IFToMM World Congress, Besançon (France), June18-21, 2007 CK-xxx An Application of an Hybrid Robot in the Total Knee Replacement Procedure Stefano Bruni * Pietro Cerveri ** Ivan Espinosa § Politecnico di Milano Politecnico di Milano Politecnico di Milano Milano, Italia. Milano, Italia Milano, Italia. Abstract—This work presents the design of a portable robot that can be easy handled in the surgical room, the robot presents an hybrid structure that permits to realize in a simple way the different milling bone cut planes to implant the prosthesis into the knee patient, the robot size, weight an functionality can make easier its operation in the surgical room. Keywords: Medical Robot, Hybrid Structure I. Introduction Total knee replacement procedure (TKR) is a common practice in orthopedics. This procedure is only recommended when the patient presents a total malfunction of the knee. The procedure consists in inserting a prosthesis that will replace all the anatomical knee. The Mechanical axis of the Femur is the line between the center of the circular head of the Femur and the center of the knee. The Mechanical axes of the Tibia is the line between the center of the Tibia and the center of the ankle at the 54% of the distance between the lateral medial melleous bone [1], [2], [3] see figure 1. Mechanical axis of the Femur Mechanical axis of the Tibia Mechanical axis of the Femur Mechanical axis of the Tibia Fig. 1. Mechanical axis of the Femur and the Tibia. the load between the hip and the knee is transmitted in the direction of the Mechanical axis of the Femur, the load between the ankle and the knee is transmitted in the * stefano.bruni@polimi.it ** pietro.cerveri@biomed.polimi.it § ivan.espinosa@mecc.polimi.it (Ph.D. Student) direction of the Mechanical axes of the Tibia [1],[2],[3]. The mechanical axes of the Femur and Tibia can be established introducing reference points or markers in the patient, images of this markers are collected with a set of telecamaras, the position of the markers are determined using photogrammetric techniques., this system is frequently used in orthopedics practice and is called navigation system [1],[4],[5], the navigation system will help the surgeon to insert the prosthesis aligned with the mechanical axis of the Femur, see figure 2. Mechenical axis of the Femur Knee Prosthesis Mechenical axis of the Femur Knee Prosthesis Fig. 2. Mechanical axis of the Femur aligned with the prosthesis axis. In general the bone cuts in the patient knee are performed by the surgeon utilizing special cutting guides, that can be oriented by a navigation system. This method presents good results in the TKR procedure, but in some occasions the bone cut takes more than 45 minutes, in this case the procedure time is an inconvenient of this method. Some surgeons also resolve the knee bone cuts for the TKR procedure utilizing robots with good results, some of this robots are: ROBODOC [6], [7], CASPAR [1], and Acrobot [8], [9], these robots presented an structure higher than one meter., ROBODOC has an SCARA structure with an special serial end-effector, ACROBOT presents an serial structure with also an special end-effector and CASPAR is an industrial adaptation of an Stäubli XR-90. Acrobot has a cooperative control between the surgeon and the robot, the system only operate in a constrain work space defined by the surgeon, preventing drawbacks of the system, on the other hand ROBODOC and CASPAR present an automatic control scheme to realize the bone cuts in the patient, the robots are assisted by a previous planning and navigation techniques in the case of CASPAR, it had been reported some drawbacks, in the