## Problem using cluster marker set using Vicon ProCalc

Dear All,

I am having some issues with creating model kinematics on Vicon ProCalc using a modified plug-in-gait lower body marker set (additional cluster markers on thigh and tibia segment). I have no experience of writing scripts on MATLAB, Python or BodyBuilder so am ideally hoping to solve this using ProCalc.

I have tried two methods of calculating knee angles using a cluster marker set these are as follows;

* adding markers to a standard plug-in-gait trial on Nexus and saving as a new .vst

* opening this on ProCalc to create segments for the thigh and tibia using the 4 marker cluster on each segment respectively

* using the created segments to formulate an Euler angle sequence for the knee (replicated the Euler sequence from standard PlugInGait calculation)

The issue with this first method is the Euler angle displays through the standard plug-in-gait thigh marker and there seems to be in inability to set a joint origin when using segments created from a 4 point cluster (which would be the knee joint centre), whereby the Euler angle would be from this point.

The second method attempted was:

* Creating a cluster point (1 virtual marker from the 4 physical cluster points) for both the tibia and femur cluster plates.

* Set the main and secondary axis vectors, from which a virtual knee joint centre could be calculated

* From this segments were created using the virtual knee joint centre and the Euler angle sequence

This displays a very similar (but different) angle through the joint centre, which is what we want. However, I don't feel this is correct as it will depend on the location of the cluster (which cannot easily be accurately placed in the same anatomical location). My understanding of the benefits of cluster marker sets is they use markers not placed in a specific anatomical location but normalised to one known location (lateral knee marker/ASIS) from which the segment position is normalised to that. Currently my understanding of our calculations would not be able to do this through creating 1 point of the four marker locations?

Many Thanks,
Ashley