A novel knot-tying approach for minimally invasive surgical robot systems.

BACKGROUND

In robot-assisted minimally invasive surgery (MIS), knot-tying is an important but challenging task for surgeons when performing surgery by manipulating a master-slave robot system. Knot-tying in the conventional way is restricted by a confined workspace, which may cause the suture loop to be unstable and make knot-tying difficult and time-consuming in robot-assisted MIS.

METHODS

A knot-tying approach named 'bending-twisting knot-tying' (BTKT) has been developed for robot-assisted surgery systems operating in a confined workspace. The non-linear deformation of sutures during knot-tying is qualitatively described using knot theory. The length ratio of a knot (LoK) and the feasible coefficient (Fc) are introduced to evaluate the quality of BTKT knots. Simulations and experiments are performed based on finite segment dynamic models and the MicroHand surgical system, respectively, to describe the dynamic behaviours of the knots. Sensitive parameters, including the length of a suture (L), the distance between two ends (d) and the angle between tangents of the two ends (alpha) are analysed based on the model.

RESULTS

For a terylene suture, the length of the suture L and the distance between the two ends d should satisfy 1.12d< or =L< or =14.4d. When L and alpha are constant, the smaller d is, the larger are LoK and Fc relative to different sutures. A knot of high quality can be tied with a small alpha.

CONCLUSIONS

Simulation and experimental results show that BTKT requires a smaller workspace and can form more stable loops compared to conventional methods.