IEEE/ASME TRANSACTIONS ON MECHATRONICS, VOL. 15, NO. 3, JUNE 2010 471 Tool Path Generator for Bone Machining in Minimally Invasive Orthopedic Surgery Naohiko Sugita, Taiga Nakano, Takeharu Kato, Yoshikazu Nakajima, Member, IEEE, and Mamoru Mitsuishi, Member, IEEE Abstract—The generation and optimization of tool paths are considered to be challenging problems for the use of a milling robot in minimally invasive orthopedic surgery. The objective of this study was to minimize the collision of the cutting tool with soft tissue, and we propose a novel approach to tool path generation and optimization. Starting with the physical requirements, we modeled some important components, and on the basis of this model, we propose a geometric optimization approach to improve the tool path. Case studies show the validity of this approach. We developed software for the application, and then evaluated the effectiveness of the application. Index Terms—Biomedical equipment, bones, cutting, machine tool control, manufacturing automation. I. INTRODUCTION K NEE arthroplasty is conducted to reduce the pain caused by joint destruction resulting from osteoarthritis or rheumatoid arthritis, as well as to enhance the patient’s qual- ity of life (QOL). As shown in Fig. 1, when the original joint is replaced, damaged articular bone is removed to fit the set- ting plane for the highly precise artificial joint. Inappropriate joint positioning and orientation adversely affect postoperative limb positioning, causing postoperative pain, and shortening of the lifespan of the new joint. Because the accuracy of a manu- ally made cut depends on the surgeon’s skill, knee-arthroplasty assistance systems have been developed to increase the bone cutting accuracy. Minimally invasive orthopedic surgery (see Fig. 2), includ- ing that used in knee arthroplasty, uses minimal incisions [see Fig. 2(a)]. This technique has advantages over conventional surgery, such as reduced pain and trauma, faster recovery, and shortened hospitalization. Minimizing the incision length to maximize cosmetic and other effects also depends on the skill of the surgeon. The cutting tool enters through the incision—the range within which the tool enters—to resect relatively large pieces of bone [see Fig. 2(b)], and many mechanical and robot- assisted surgical systems are being developed to improve this procedure. Manuscript received April 22, 2009; revised July 16, 2009. First published September 18, 2009; current version published April 2, 2010. Recommended by Technical Editor A. Menciassi. This work was supported by the Japan Society for the Promotion of Science Encouragement of Young Scientists (B) (20760081). N. Sugita, T. Nakano, Y. Nakajima, and M. Mitsuishi are with the Department of Mechanical Engineering, School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan (e-mail: sugi@nml.t.u-tokyo.ac.jp). T. Kato is with the Halley Valley Company Ltd., Hamamatsu 430-0929, Japan. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMECH.2009.2030184 Fig. 1. Artificial knee joint. Fig. 2. Tool path in minimally invasive surgery. (a) Minimally invasive surgery. (b) Resection planes. Minimal invasiveness, high accuracy for the cut surface, high efficiency, and machining safety are all required in mini- mally invasive orthopedic surgery. The minimally invasive knee- replacement technique attempts to meet these requirements through the smallest possible incision. The knee joint is then accessed through the quadriceps tendon. This procedure is said to be less damaging to soft tissue and bone than other proce- dures. The accuracy of the shape of the setting plane is important for fitting the artificial joint, and the absolute position of the arti- ficial joint must be precise. The operation time for bone cutting 1083-4435/$26.00 © 2009 IEEE