SPECIAL FOCUS PAPER HAPTIC POSITIONING ENVIRONMENT FOR THE HIP RESURFACING SURGERY Haptic Positioning Environment for the Hip Resurfacing Surgery http://dx.doi.org/10.3991/ijoe.v8iS1.1890 P. Pires, P. Teodoro, J. Martins and J. Sá da Costa TULisbon, Lisbon, Portugal Abstract—The development of new robotic surgical instru- ments has brought significant improvements to the execu- tion and outcome of surgical procedures. They allow shorter intraoperative interventions with higher precision of the surgical gesture, which has clear benefits for the patients, surgeons and hospitals. Perhaps the main retardant of the widespread of these new tools is the ability of getting the surgeon’s hands-on with the new systems, for both initial evaluation and later on to overcome the initial learning curve. To accelerate this stage, and keep costs to a mini- mum, simulation tools have been introduced which allow physical surgeon-patient interaction through haptic devices. In this work, we focus on the Hip Resurfacing Surgical Pro- cedure, and develop an interactive virtual environment for the insertion of the hip resurfacing guide wire with high precision and accuracy. The surgical tool used is a robotic arm that allows geometric accuracy and repeatability while the surgeon keeps control over the force exerted on the pa- tient. Index Terms—Biomechatronics, Human robot interaction, Medical robotics, Simulation. I. INTRODUCTION In the last two decades, haptic systems have been an ac- tive area of research, where surgical training environments are an important area of focus for haptic devices. The pos- sibility to train surgeons without the need of cadavers and animals reduces costs and eliminates ethical issues that may arise [1]. In this paper, a haptic system and virtual environment are integrated for simulating the guide wire insertion into the femural head in the hip resurfacing surgical procedure. The haptic device used is the Novint Falcon, and the vir- tual environment is created in Matlab/Simulink for fast implementation of control algorithms, despite of all the necessary interface development [2]. A modified Hertz Law is used to model the bone-tool interaction force, and a variable impedance force law is used for the virtual sur- gical robot to guide the surgeon’s hand to the correct posi- tion over the femur. This paper is organized as follows. Section II introduces the surgical procedure. Section III presents the hardware interface along with the environment force fields. Results are presented in Section IV, followed by conclusions in Section V. II. PROBLEM STATEMENT Total hip resurfacing is a technically demanding surgi- cal procedure and as any other procedures has a signifi- cant learning curve. In [3], a study of a single surgeon’s Figure 1. Left - McMinn Alignment Guide, from [4]. Right - Birming- ham Hip Resurfacing prosthesis. learning curve was performed where the quality of the implant position was measured. A relevant conclusion is that there is significant variability on the implant position- ing. The position of the femoral implant is of extreme importance for the surgery success. Measurements ob- tained from the preoperative planning are evaluated in order to obtain the desired position of the femoral guide wire, Fig. 1. A robotic arm may aid the surgeon to perform the pro- cedure by actively guiding the drill to the correct orienta- tion and position, [5]. It minimizes the risk of incorrect positioning during drilling and a reduction in surgery time is expected, as well as a significant increase in geometrical accuracy and precision, [6]. III. PRELIMINARIES A. Haptic hardware interface The haptic system used is the Novint Falcon device that communicates with the host computer through a USB 2.0 port, figure 2. It has three degrees of freedom with force feedback that are associated to the robot end-effector. The user thus has feedback of the exerted reaction force over the simulated patient femoral bone and the applied forces resulting from the control laws implemented. The visuali- zation processing is evaluated in a separate computer from the host computer due to sample time constraints. B. Force Field Formulation The contact model adopted in this work is the recently modified non-linear Hertz law presented in [7] that ac- commodates smaller coefficients of restitution, e . F C n  k n d n  1  81  e   5e v n v n         (1) iJOE – Volume 8, Special Issue 1: "exp.at'11", February 2012 23