Joint centre calculation

Main Forum
1

Hello Anybody

Could you explain to me how using the PiG model you calculate joint centres at the hip and the knee. I am assuming that at the hip you use a known regression equation (Davis, Bell, Harrington). At the knee you are required to normally use the knee width which is measured clinically in order to define the medial-lateral position of the joint centre. I do not think Anybody does this as I cant remember inputting a knee width value, so I would like to know how you calculate the joint centres?

Ammar

2

Dear Ammar,

If you see the definitions of the hip and the knee joints,
those joints are using their related AnyRefNode objects.

Those nodes will be scaled with the scaling function according to your scaling scheme.

If you want to apply what you think right, then you should modify the definitions of the hip and the knee joints in the AMMR directly by yourself.

Best regards,
Moonki

3

Hi Ammar

I think you have the wrong conception of what AnyBody does when scaling the models. In fact, the model is only scaled linearly and some marker positions are optimized. The concept is different from what you see in traditional gait analysis where the model is completely defined by the markers. It is conceptually different. A good explanation of what AnyBody does is given by Andersen:

http://www.tandfonline.com/doi/abs/10.1080/10255840903067080

That also means that you won’t get the exact same kinematic output as the PIG model in vicon.

You can also use the traditional approach with AnyBody. I published an example of that last year:

http://vbn.aau.dk/files/207637041/Lund_2015_Scaling_of_musculoskeletal_models_from_static_and_dynamic_trials.pdf

/Morten