ARTHROBOT : A New Surgical Robot System for Total Hip Arthroplasty Dong-Soo Kwon*, Yong-San Yoon*, Jung-Ju Lee*, Seong-Young Ko*,Kwan-Hoe Huh*, Jong-Ha Chung*, Young-Bae Park*, Chung-Hee Won** * KAIST Mechanical Engineering Department (e-mail: kwonds@me.kaist.ac.kr) ** Chungbuk University Hospital (e-mail: chwon@med.chungbuk.ac.kr) Abstract This paper presents mechanisms and control methods of a new surgery robot for total hip arthroplasty (THA). To minimize the disadvantages of the conventional registration method, a new gauge-based registration method has been proposed, and a 3-DOF robot has been developed that can be mounted on a femur. The proposed surgical robot can operate along a pre-programmed path autonomously, in addition to allowing a surgeon to directly control the motion of the surgical robot with their experience and judgment during an operation. For this purpose, a master is attached to the surgical robot and admittance display is used in control. ARTHROBOT, this new arthroplastic surgical robot system, is expected to be adaptable to surgical needs and practice in the operating room. 1. Introduction Either by trauma or disease, a hip joint can be damaged, and this induces pain and reduces the range-of-motion in the hip joint. In this case, Total Hip Arthroplasty (THA), which is the name of an operation for replacing the damaged hip joint with an artificial hip-joint, is performed. The artifical hip joint is composed of an acetabular component and a femoral stem, the stem being either one of two types, cemented or cementless. As its name suggests, a cementless stem does not need cement because the bone grows into the porous part on the stem and the stem is fixed to the femur. When using a cementless stem, the conformity between the bone and the implant greatly affects the success of the surgery and the recovery of the patient [1]. Thus it is very important to carve a hole in the femur that precisely fits the shape of the artificial hip implant in order to increase conformity and minimize gaps. In a conventional cementless THA, the surface conformity between the bone and the implant is less than 30%. This causes slow recovery and shortens the life of the implant [2]. To improve this situation, robotic surgical systems that can make a precise cavity in the femur were developed [3]. In particular, Integrated Surgical System Co. developed a commercial THA system, the ROBODOC® Surgical Assistant System [4]. By using these surgical robots, the surface conformity can be improved and patients can recover more rapidly [5]. In such robotic systems, to register the surgical robot to the femur, the fiducial markers are implanted onto the femur of a patient before surgery, and a CT scan of the femur is performed. In real surgery, the robot system is registered through comparing the measured positions of the markers and the positions of the markers in CT scans. This paper introduces a new arthroplastic surgical robot system which we call ARTHROBOT. Since a small surgical robot is mounted onto the patient’s femur by a bone clamp, the registration procedure becomes simple, and the cost of the operation can be reduced. Since the robot has a master/slave-combined structure, a surgeon can directly control the motion of the surgical robot like an advanced surgical tool. Through an admittance display, the surgeon can feel the comfortably pre-defined virtual environment. Also a virtual hard wall is displayed at the surgical boundary to ensure surgical accuracy. 2. Gauge-based Registration Method / We have proposed a greatly simplified cavity machining method for robot-assisted total hip athroplasty surgery that requires neither CT scanning nor the insertion of fiducial markers before surgery [6]. In this technique, a surgeon prepares the distal portion of the femoral cavity using a conventional manual reaming process which centers the distal end of the cavity relative to the cortical bone. Next, the surgeon inserts a reamer-shaped registration gauge into the prepared distal cavity aligning the front of the gauge with the direction of the femoral neck; this defines the orientation for the final implant (Fig. 1). The surgeon then attaches the base for a small surgical robot to the gauge part of an external femoral clamp using an adjustable linkage consisting of two sets of ball and socket joints and a slider. Both the base frame and the registration gauge have matching mating surfaces so that, with the linkage unlocked, the surgeon can maneuver the base frame into solid contact with the registration gauge (Fig. 2). Proceedings of the 2001 IEEE/RSJ International Conference on Intelligent Robots and Systems Maui, Hawaii, USA, Oct. 29 - Nov. 03, 2001 0-7803-6612-3/01/$10.00 2001 IEEE  1123