A study of sustained forces and of the working space of endoscopic instruments.

The instruments currently used in endoscopic surgery are limited by several factors, in particular their reduced working space. In order to develop instruments with manifold degrees of freeedom (DOF), the elementary actions performed by the existing instruments must be defined. Material and methods:We have broken down into elementary movements the actions performed by the currently used instruments and analyzed them by measuring the strain on the instruments and on their working volume. The elementary actions were performed in vitro (Pelvitrainer) on an animal model (pig) and also in the course of clinical practice. A total of 6,750 measurements were carried out for the following actions: grasping, cutting, dissecting, suturing and knotting. Results: The largest working volumes were measured for the knotting and suturing actions (198 degrees in axial rotation and 69 degrees in lateral translation). The range of the working space was between 8 degrees and 52 degrees. Forces exerted on the instrument were between 0.5 and 12 Newton (N). Forces exerted on the headpoint were between 0.4 and 10.5 N whereas the friction forces were between 0.5 and 1.5N. Comments: By analyzing the elementary actions of endoscopic surgery, we were able to quantify the directions and dimensions of forces sustained by the instruments and were also able to measure the working volume involved when performing the main actions in endoscopic surgery. The results obtained provide a basis for the development of more sophisticated instruments.