Suturing Modeling and Simulation in the virtual lower limb surgery simulation system

Real-time virtual suturing simulation for lower limb surgery requires both biomechanical accuracy and computational efficiency-a balance that existing methods struggle to achieve. Geometry-based models sacrifice physical realism, whereas physics-based techniques like FEM and mass-spring models frequently encounter complexity and instability issues. To overcome these limitations, we present a hybrid physics-based framework that merges Kirchhoff rod theory with extended position-based dynamics (XPBD). Our approach models the suture as a discretized rod with stretch, bending, and torsion constraints, and integrates its interaction with a rigid needle and anisotropic viscoelastic soft tissue. Through a prioritized constraint-solving scheme, the system maintains real-time performance without compromising mechanical fidelity. Validation against a high-fidelity reference confirms comparable dynamics in gravity-release and damped oscillation tests, along with a 16-21% decrease in computation time under real-time step conditions. Importantly, the simulation realistically reproduces force profiles across needle puncture, thread pull-through, and knot tying, including clinically meaningful mechanical transitions such as tissue indentation, frictional sliding, and stress relaxation. The framework thus provides physically credible suture mechanics while operating within real-time constraints. This study delivers a robust computational tool for simulating complex surgical suturing, with potential uses in training, procedural analysis, and VR surgical platform design.