Tensile strength of surgical knots performed with the da Vinci surgical robot

The objective of this study was to estimate the tensile strength of surgical knots made using the da Vinci robot. Four different types of flat square knots (strand-to-strand 4 throw, strand-to-strand 6 throw, loop-to-strand 4 throw, and loop-to-strand 6 throw) were made using the da Vinci-S system by 4 different surgeons, all experienced with the system. For the knots, we used braided polyglactin 910 (Vicryl 2-0). Hand-tied, flat, square, 4-throw strand-to-strand knots were used as reference. The tensile strength was measured for all knots using the Instron 5566 system calibrated to an accuracy of + or - .5% at 4 to 10 newtons (N) and + or - .4% at greater than 10 N. Compared with reference knots, only 1 of 4 surgeons could make knots as equally strong with the robot. For all surgeons, strand-to-strand knots had a significantly higher tensile strength than loop-to-strand knots when made with the robot. Adding 2 throws to the knot did not increase the knots strength in the robot. It is possible to make equally strong surgical knots with the da Vinci robot as by hand; however, despite previous experience with the robot, only 1 of 4 surgeons managed to do so. Adding 2 throws to R4SS and R4LS knots did not increase the tensile strength significantly for any of the 4 surgeons. It is important to train and tie knots using the da Vinci system with the same care as by hand and to be aware of possible differences in knot-tying technique with the robot and manually. With the robot, strand-to-strand knots were stronger than loop-to-strand knots, and should be preferred.