Stitching Planning in Laparoscopic Surgery: Towards Robot-assisted Suturing

The work presented in this paper addresses the problem of the stitching task in laparoscopic surgery using a circular needle and a conventional 4 DOFs needle-holder. This task is particularly difficult for the surgeons because of the kinematic constraints generated by the fulcrum in the abdominal wall of the patient. In order to assist the surgeons during suturing, we propose to compute possible pathes for the needle through the tissues, which limit as much as possible tissues deformations while driving the needle towards the desired target. The paper proposes a kinematic analysis and a geometric modeling of the stitching task from which useful information can be obtained to assist the surgeon. The description of the task with appropriate state variables allows to propose a simple practical method for computing optimal pathes. Simulations show that the obtained pathes are satisfactory even under difficult configurations and short computation times make the technique useful for intra-operative planning. The use of the stitching planning is shown for manual as well as for robot-assisted interventions in in vitro experiments. 1 Clinical and technical motivations Computer assisted interventions have been widely developed during the last decade. Minimally invasive surgery is one of the surgical fields where the computer assistance is particularly useful for intervention planning as well as for gesture guidance because the access to the areas of interest is considerably restricted. In keyhole surgery such as laparoscopy or thoracoscopy, the surgical instruments are introduced into the abdomen through small 1 tissue to be sutured needle O∗ exit point I∗ entry point endoscope abdominal wall trocar needle-holder Figure 1: Outline of the laparoscopic setup for suturing with desired entry point (I*) and exit point (O*) incisions in the abdominal wall. The vision of the surgical scene is given to the surgeon via an endoscopic camera also introduced in the abdomen through a similar incision (see figure 1). This kind of surgery has many advantages over conventional open surgery : less pain for the patient, reduced risk of infection, decreased hospital stays and recovery times. However the surgical tasks are more difficult than in conventional surgery which often results in longer interventions and tiredness for the surgeon. As a consequence, laparoscopic surgery requires a specific training of the surgeon [12]. The main origins of the difficulties for the surgeon are well identified [30]. Firstly, the fulcrum reduces the possible motions of the instruments and creates kinematic constraints. Secondly, surgeons encounter perceptual limitations : tactile sensing is higly reduced and the visual feedback given by the endoscopic camera (laparoscope) is bidimendional and with a restricted field of view. Hence, it is difficult for the surgeon to estimate depths, relative positions and angles inside the abdomen. Finally there are perceptual motor difficulties which affect the coordination between what the surgeon sees and the movements he performs. According to laparoscopic surgery specialists, the suturing task is one of the most difficult gestures in laparoscopic surgery[4]. The task is usually performed using two instruments : a needle, often circular, and a needle-holder (see figure 2). Suturing can be