Influence of different trocar tips on abdominal wall penetration during laparoscopy

Most trocars currently used to place a cannula through the abdominal wall have a conical or pyramidal tip. Because the risk of inadvertent injury along with removal of the cannula is probably related to (a) the force needed to traverse the abdominal wall, (b) the force needed to remove the trocar, and (c) the defect in the abdominal wall, the optimum configuration of the penetrating tip should be determined. The entry force needed to perforate the abdominal wall, the removal force necessary to remove the trocar, and the defect in the abdominal wall were measured in a porcine model under standardized conditions (general anesthesia, 12 mmHg pneumoperitoneum). Nineteen trocars (six disposable, seven reusable, six custom-made) have been tested. They were divided into six groups according to the shape of the tip (conical, pyramidal, or a combination). The entry force (F = 25.6, p < 0.0001) and the removal force (F = 5.1, p < 0.01) were related to the shape of the tip. Conical tips needed a higher force than purely pyramidal tips. The abdominal defect was also different between groups (F = 6.5, p < 0. 001). The trocar with a pyramidal shape caused a greater defect than conical tips. The defect in the abdominal wall was inversely related to the entry force (r = -0.55, p < 0.001) and to the removal force (r = -0.57, p < 0.001). There is not an optimum configuration of a simple push-through trocar with a low entry force and a high removal force. Some kind of a conical tip is recommended for insertion of trocars under direct view.