Adding a Spring Between Vertebrae to Simulate Spinal Stabilization

[Filip Ryšavý]

Dear OpenSim Community,

My name is Filip, and I am a student currently working on a project where I aim to simulate spinal stabilization by adding a spring element between vertebrae in an OpenSim model. Specifically, I am focusing on the L5-S1 segment and trying to model the stabilization effect on adjacent segment loads during dynamic simulations.

I ve successfully managed to implement a PathSpring between the segments using MATLAB, but I am struggling with setting the correct parameters and ensuring that the spring is anatomically and functionally accurate. My questions are as follows:

Positioning the spring: What is the best approach to determine the exact start and end points for the spring? Should I use specific offsets or reference frames tied to the joints?

Spring parameters: How do I decide on appropriate values for stiffness, damping, and resting length to simulate a realistic stabilization effect?

Validation: Are there any best practices for validating the placement and behavior of the spring in OpenSim? For example, should I expect a specific change in load distribution on stabilized versus non-stabilized segments?

I would be incredibly grateful for any advice, example scripts, or references to similar projects. Thank you in advance for your guidance and support!

Kind regards,
Filip

[Nicholas Bianco]

Hi Filip,

Thank you for your post. I have one brief suggestion, which is that you might find the class ExpressionBasedBushingForce useful for modeling vertebral passive forces. It will allow you to define passive 3D force and torque expressions that are a function the relative orientation and displacement of two bodies.

Best,
Nick