Define specific portions of pelvis thorax extension for each joint of spine

Hello, everybody!
As a default, the PelvisThoraxExtension angle is equally partitioned between the T12–L1 through L5–S1 segments. I need to define each joint's specific percentage based on a paper I'm working on. How can I do this?
Is it needed to change SRMatrixes.any Coefficients? if so How? I tried it then I got so many errors!
and Where can I check in the Study that it is achieved correctly and not forced to change by the drivers?

Thank you for your attention

Hi @Mawsen

To get the control you need, you probably need to switch of the default spine rhythm and implement your own drivers for the joints.

Best regards,

I switched off the Spine Rhythm Driver and tried to define a function like the one in the SpineFixationWithForceDepKinematics example but I received an error that indicates the 18 DOF of six joints are not constrained.
Can you tell me how I can debug this function? Or is there any example of spine rhythm function that takes a weight vector given to each joint to distribute the overall thoracopelvic angle?

Hi @Mawsen

Try to go one DoF at a time if you are having trouble with controlling all at once.
Either implement a simpler constraint and then start adding them one-by-one to your rhytm or keep the old and pick them on at a time.

I don't have the example rhythm you are looking for unfortunately

Best regards,

Hi Bjørn,

Thanks for your response. I have another question, what is the difference between SacrumPelvisJnt and PelvisRotZ? In the HumanStanding model, the input value of PelvisRot cannot be achieved after running the model but the angle of SacrumPelvisJnt can be.

As I know the flexion of Thorax (T) is the sum of Lumbar and Pelvis flexions

T = L + P
L = PelvisThoraxExtension
P = PelvisRotZ

For different flexions, PelvisThoraxExtension would be the same as I entered after running the model but because of some drivers, PelvisRotZ would be different from the one that I entered, thus, Thorax flexion wouldn't be the one that I intended. Does it make sense if I add SacrumPelvisJnt to this simulation and achieve P by the sum of PelvisRotZ and SacrumPelvisJnt?

P = PelvisRotZ + SacrumPelvisJnt angle



Hi @Mawsen

  • The PelvisRotZ is a measure representing the rotation of the pelvis around the z-axis which you can set in the mannequin file before loading or use in your drivers to add or restrict motion of that measure.
  • The SacrumPelvisJnt is a spherical joint connecting the pelvis and sacrum.

I'm not sure to which angle of the sacrum-pelvis joint you are referring?

The PelvisThoraxExtension is again a measure as the pelvis rotation. This can control the flexion-extension of the thorax and be set before load is a initial position or used in drivers to impart/restrict motion.

You can have a rotated pelvis while maintaining 0 degrees of thoracic flexion. And do the opposite - flex the thorax without rotating at the pelvis.

These measures you mention are often part of model drivers which is why the values change during the simulations.
If you drive the measures to the values you want - they will stay like that or results in errors if the system cant be solved due to conflicting constraints.

If your goal is to control the thoracic flexion then you can use the PelvisThoraxExtension parameter in a driver.

Best regards,

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