RASI/LASI marker set - I am using markers on greater trochanter

Dear Sir/Madam
I have a question about our marker set different from the one from Anybody model.
I am trying to do inverse dynamic analysis by using ‘GaitLowerExtremity.main.any’.
We are using the markers on ‘greater trochanter on Femur’ instead of RASI/LASI in Pelvis because most of our subjects are obese and hard to put marker on pelvis.
As long as I know, the motion of pelvis and femur are independent so RASI/LASI positions are not acquired by offsetting the markers on greater trochanter. And I think RASI/LASI markers are important for generating motion of lower limbs and not allow to ignore during analysis and simulation.

I suppose, I am not the only user having same problem. Could you let me know where is previous Q&A or dome documents regrading these kind of problem?

Thank you
Seungkook Jun

Dear Seungkook Jun,

All our models use markers on the pelvis. The Pelvis is a separate segment, so you need some information to drive it. Idellay this is done by 4 markers R/LASI and R/LPSI; You could also reduce it to 3 R/LASI and SACR.
I don’t think it will be easy to use the greater trochanter markers instead. You can try and cahnge it, but I’m not sure that it will work. You can constrain also the motion of the pelvis with separate drivers, but this will also affect accuracy and make it more difficult.

Do you have any other markers on the upper body?

Dear Amir
Thank you for your reply.
Our marker set is attached.,

Thank you
Seungkook Jun

Hello Seungkook Jun,

I see 2 options:

  1. Just exclude RASI and LASi. I’m not sure if it will work. exclude them in the ModelSetup file and in the part for initial positioning. Then see what happens? It might fail though.
  2. Use RGT and LGT instead. I’m not sure either of this will work. There will be conflicts, because they are in reality connected to the femur and the femur will move in relation to the pelvis. A solution might be to decrease the weight (importance) of this marker.