Model Outputs

This document describes the outputs that are measured from the simulation results. Time is used to index the application of external loads and prescribed displacements/motions. The model outputs can be measured at specific time points throughout the test cycle. Custom Python scripts are used to extract these measurements from the simulation’s results file (.odb for Abaqus).

Contact

Contact measurements can be directly measured from the simulation. Between each contact pair (Table 15) the contact metrics are:

  • Total contact area
  • Total contact force (magnitude)
  • Contact pressure distribution
Table 15 The contact pairs where contact area and total contact force are measured from.
Femoral cartilage Tibial cartilage - medial
Femoral cartilage Tibial cartilage - lateral
Femoral cartilage Patellar cartilage

Joint Kinematics

The connector elements are used to measure joint kinematics from the simulation results. The connector elements are aligned with the joint’s coordinate system, so joint translations and rotation are directly related to each connector’s translation and rotation. Note that the connector’s initial position is defined when the joint is in the image state (i.e. the joint position/orientation in the MR image), so the initial joint position/orientation should be taken into account when measuring joint kinematics.

Ligament Force

The ligament force is defined as the magnitude of force carried by the ligament. It is taken as the sum of forces magnitudes carried by each ligament fiber. Each fiber’s force is taken as the average force magnitude carried by the elements in the fiber. The elements in each fiber should carry a similar force magnitude, however the forces may be different due to ligaments wrapping around surfaces.