Comparison of abdominal-wall stretching between basic and enhanced laparoscopic instruments

In laparoscopic surgery, access to the patient's abdomen is gained by using an instrument, consisting of a 300-400 mm long stem with attached tool, in serted through a cannula mounted in the patient's abdominal wall. Sliding o f the stem relative to the cannula and rotation of the stem about its longi tudinal axis are the only motions not constrained by the abdominal wall. Th ese limited-motion capabilities necessitate abdominal-wall stretching for f ull-spatial tool displacements. Abdominal-wall stretching is potentially da maging to the patient and fatiguing to the surgeon. Minimization of stretch ing is shown to be possible by the addition of a single revolute joint to t he basic instrument. The motions allowed by the stem and cannula, the addit ional joint, and the abdominal wall result in a kinematically redundant sys tem; i.e., an infinite number of joint displacements exist to achieve a des ired tool position and orientation (desired tool pose). An optimization tec hnique is applied to determine the minimum stretching for desired tool pose s. Elimination of stretching is shown to be possible by the addition of two revolute joints to the basic instrument. Displacement models for the basic and enhanced instruments are found using concepts of manipulator kinematic s. Forward and inverse displacement solutions for the instruments are found . The inverse displacement solutions are used to compare the amount of stre tching required by each instrument. The stretching is highest for the basic instrument. The instrument with one additional joint produces stretching t hat is always less than or equal to that of the basic instrument. The instr ument with two additional joints eliminates the need for stretching. (C) 20 01 John Wiley & Sons, Inc.