Several of the default labeling templates, including the one that is supplied for CGM2.3, use a hinge joint (a single degree-of-freedom joint) at the knee. Hinge joints work well to constrain the VST when it’s used for labeling only, but because CGM uses a ball joint (three degrees of freedom) for all joints, you must update the labeling template (VST) to use ball joints.
To update the joints in a VST:
- Load a static trial and create a new subject based on the labeling template.
- Reconstruct and label the static trial.
- Run a Kinematic Fit operation on the trial.
The current segments and joints are fitted to the marker data.
- In the Subjects Resources pane, expand the subject node and then expand the Joints node to display the joints in the template.
The hinge joints are clearly labeled with a 1 symbol.
- Select the hinge joints, then right-click and select Unlink Joint.
The symbols change from 1 to 6 to indicate that the hinge joints have been replaced with 6-degree of freedom joints:
- Re-link these joints using the Link Segments tool in the Labeling Template Builder. To do this, on the Subject Preparation Tools pane, in the Labeling Template Builder section, select Ball Joint and click Link:
A tip next to the mouse pointer prompts you to select the parent segment.
- In the Subjects Resources pane, expand the Segments node of the subject.
- Click on the L_Femur segment to select it.
You are prompted to select the child segment.
- Click on the L_Tibia segment.
The list of joints now shows that the L_Femur_L_Tibia joint is now a ball joint with the symbol 3.
- Repeat Steps 8-9 for the right side.
- Right-click the subject and select Save Labeling Skeleton as Template.
- Select a new name for the template, then save.
The template has now been updated with ball joints instead of hinge joints for the knees.