Joint Stress Analysis

   
Figure 6: Stress loading and visualization for a slice of the femur model.

Joint stress analysis meshes the bones, calculates the loading from the dynamics [13], and invokes a finite-element package (ABAQUS). The modeling requirement is to reconstruct smooth bone models from rough clinical data. The visualization requirement is to display the computed tensor field of stresses superimposed on the joint model. Flexible body dynamics computes large-scale motions of parameterized deformable objects, such as generalized spring-damper systems, by integrating Lagrangian equations. The modeling requirement is to construct parametric models of muscles, ligaments, and cartilage (the deformable parts of joints) from clinical data. Rigid and flexible dynamics share the modeling requirement of computing the material properties of the bones from the clinical data and share the visualization requirements of displaying the motion of the bones and the contact forces, which specify vector fields in physical space.
In our Shastra environment [1], a set of distributed tools are used in a collaborative manner to complete the various stages of analysis. Modelling from images is performed by a medical imaging toolkit, with results communicated directly to a finite element preprocessor and visualization tool. Here the model is meshed to user specifications. Material properties for the mesh are computed directly from the CT data, and boundary conditions are interactively specified by one or more collaborating users. Analysis is performed by one of several external solvers which are supported in the environment, and results are read back into the system for post-processing and visualization. An example stress loading of a slice of bone from a femur is given in Figure 6.