Soft-Tissue and Needle Modeling for a Real-Time Finite Element Based Bi-Manual Surgical Suturing Simulator

Alex Lindblad, University of Washington

Surgical suturing is a skill not taught in a virtual environment due to the inherent computational costs that prohibit realistic behavior from being simulated in real-time. This research presents a new method in soft-tissue modeling that more accurately represents skin and soft tissue allowing for skin undermining and repositioning, as well as techniques for needle-tissue interaction during suture placement, all in the context of a bi-manual finite element based haptic surgical suturing simulator.

Representing the soft-tissue as volumetric elements and the skin as two dimensional plane stress elements allows the model to incorporate the vastly different material properties in each; and giving each type of element its own distinct set of nodes allows for dynamic repositioning of the skin elements over the tissue elements. Using displacement constraints, the skin and tissue are forced to deform together; removing these constraints, coupled with low-rank matrix updates, allows the skin to separate from the subcutaneous tissue, and formulating a new set of constraints allows the skin to reposition on different tissue below.

The needle, at initial contact, is modeled as a rigid displacement constraint, thus forcing the tissue to displace according to the needle position. After the needle has penetrated the skin its lateral movement is still modeled as rigid displacement constraints, while longitudinal movement is modeled as a body force at the tip of the needle with haptic resistance coming from an empirical tip reaction force. This allows the tissue to deform based on needle movement while giving the user a realistic look and feel. The goal of this research has been to create interactive models that will add a level of realism to surgical suturing simulators not yet seen.

Abstract Author(s): Lindblad, A.J., Turkiyyah, G.M.