Validation of the shoulder model + Friction induced force shift at the shoulder joint

Main Forum
1

Hi guys,

I’m presently trying to validate the shoulder model by comparing the results to the published literature. When I compare the results of Bergmann (2006) (instrumented prosthesis) with those of the BergmannGH model (using percentage body weights and no supraspinatus), I found similar results, but I’m still convinced that the model needs further improvements. In a modified BergmannGH model that I work on, I simulate all the other movements of the shoulder that are not simulated in the BergmannGH model, i.e. clavicular rotations, scapular upward rotation and glenohumeral external rotation. However, the results that I get are even less close to what i get from the original BergmannGH model.

In the study of Bergmann (2006) they discussed about a friction induced force shift at the shoulder which reaches 5.3 mm, i.e. the highest value of all the performed movements, during an abduction of 45 degrees. Do you think that replicating this friction in the model would lead to closer results ? If yes, is there a mean to replicate this force shift (or the resulting friction moment) in the shoulder model using, for example, the friction toolbox ?

Thank you for you support.

Pierre

2

Hi Pierre,

There is a new version of the repository that has been released together with version 4.2 of AMS. It contains a rhythm for the shoulder complex that you could use in the BergmannGH model, my guess is that it should improve it.
You can get the repository together with v4.2 instaler or from the repository project on anyscript.org.

About the friction it is possible to add it with the friction tool box if you know the friction coeficient. It will require some modifications of the GH reactions, that should be done carefully (i think the pushing muscles should still be between the scapula surface and the humerus center, but the friction muscle should act between the two surfaces). I cannot really say if the results will be better or not, but it is a good idea to try it.

Best regards, Sylvain.