Joint Simulation

1. Introduction

We are developing modeling and physical simulation tools for human joints reconstructed from the CT, MRI, and photograph imaging data sets of the visible human. The objectives are non-invasive diagnostic tools, systematic preoperative planning, custom prosthesis design, and quantitative models of strain injuries. The research challenges are to compute the physics directly from the data with minimal user intervention and to compute at interactive speed despite the great size of the data sets. We address these challenges by hierarchical modeling, distributed computing, and specialized physical simulations.

The modeling tools of our system construct geometric spline and finite element models of bones from the CT data and tendon/ligaments from the MRI and photographic data. The geometric models are extended to capture material properties, such as mass distribution, elasticity, and friction coefficients. The elasticity and friction coefficients are approximated using qualitative mathematical functions of the CT and MRI intensities. The simulation module computes the joint physics (motions, forces, deformations) from the bone models, material properties, and muscle forces. The visualization module displays the raw data and the solid models, animates the dynamics, displays the stresses, and supports user manipulation and quantitative querying.

The computational requirements of the simulation module govern the design of the other modules. We organize the requirements around the tasks of reconstruction, kinematics, rigid body dynamics, stress analysis, and flexible body dynamics.