The optimal mechanical efficiency of laparoscopic forceps

Abstract

Laparoscopic forceps have a large amount of friction in the mechanism, leading to a limited mechanical efficiency, which impairs the pinch force feedback. The advantage of a small amount of friction is that it is easier to maintain a constant pinch force on the tissue. Therefore, to obtain the optimal mechanical efficiency of the forceps, the influence of mechanical efficiency on the performance of several static and dynamic operative tasks, such as grasping tissue and estimating pressure, is quantified. A grasper with adjustable mechanical efficiency and a load cell to measure the pinch force on the tissue was developed. Using this grasper, subjects performed several tasks on pig bowel tissue and simulation tissue: grasping tissue, reproducing a requested constant or variable pinch forces, and estimating the pressure in a tube. With increasing mechanical efficiency, a variable pinch force could be reproduced more accurately (deviation from the requested pinch force decreased from 34.4 to 24.9%, p = 0.016). The performance on the grasping tissue, reproducing a constant pinch force, and estimating pressure tasks did not improve with increased mechanical efficiency. The optimal mechanical efficiency of laparoscopic forceps is dependent on the task that is performed. For tasks requiring little movement of the forceps, such as grasping and holding tissue, a low mechanical efficiency is sufficient, whereas for tasks requiring repeated movement of the forceps to feel tissue, a high mechanical efficiency is required.