Patterns of failure at the instrument-tissue interface

Background. The effect of jaw design on grip security and tissue trauma is poorly understood. This project establishes an in vitro model of the instrument-tissue interface. Materials and methods. Aluminum jaws with teeth of differing size and shape gripped fresh sheep stomach with variable apposing (squeeze) pressure. The tissue was extracted at a rate of 50 mm/min until either the grip or the tissue failed. The load at which the grip failed, the maximum (peak) load generated, and the mode of failure were noted. The data were analyzed using ANOVA and a post hoc Duncan's multiple range test when appropriate. Results. Increasing the apposing pressure increased grip security. Grip security of 1- and 2-mm pitch teeth were significantly greater than for plane jaws and smaller-pitch teeth (P < 0.001). Of the wave pattern jaws, 2-mm pitch waves also had significantly greater grip security than plane jaws and smaller pitch waves (P < 0.01). Wave pattern jaws produced significantly less tissue trauma than teeth (P < 0.0001). Conclusions. Increasing the size of instrument teeth increases grip security but at the expense of tissue trauma. Wave pattern jaws result in significantly less tissue trauma than teeth. This model measures grip security precisely and allows for comparison between jaws of different patterns. (C) 2000 Academic Press.