Motion segment of the spine

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1

Hello AnyBody,

I want to develop a thoracic spine model. As I am very new with the software, I thought that it will be nice to start analyzing the motion segment that I will create. Currently, I am working on a motion segment of T3/T4 vertebra.

As a first step, I want to make the joint between these two segments (please see the attachement, T3/T4 joint) to have six d.o.f… At this joint, a stifness
matrix (6x6) will be incorporated. Upon driving the base joint of segment T4, I want to measure the forces in the ligaments and reactions at these joints
under a given force (F) applied at upper segment. Can you please explain how to do this? How can I define a six d.o.f. joint? How can I drive a six d.o.f.
joint in AnyBody? A simple example will be great.

I also attached my simple code, in case it is needed.

Kind regards,

Rıza.

2

Can anybody help me on this please?

3

Hi Riza,

You can create kinematic measures in AnyBody by doing something like:

  AnyKinMeasureOrg T3T4Joint = 
  {
    //RefFrames = ;
    //Surfaces = ;
    //KinMeasureArr = ;
    //KinMeasureIndexArr = ;
    //MeasureOrganizer = ;
    //AnyKinMeasure &<Insert name0> = <Insert object reference (or full object definition)>; You can make any number of these objects!
    AnyKinLinear lin = 
    {
      //RefFrames = ;
      //Surfaces = ;
      //KinMeasureArr = ;
      //KinMeasureIndexArr = ;
      //Type = CartesianCoord;
      //Ref = -1;
      //LineLineDistanceAxes = {{x, x}};
      //LineLineDistanceAxisLength = 10;
      //AngularAxis = z;
      AnyRefFrame &rf0 = <Insert object reference (or full object definition)>;
      AnyRefFrame &rf1 = <Insert object reference (or full object definition)>;
    };

    AnyKinRotational rot = 
    {
      //RefFrames = ;
      //Surfaces = ;
      //KinMeasureArr = ;
      //KinMeasureIndexArr = ;
      Type = RotAxesAngles;
      //Axis1 = z;
      //Axis2 = y;
      //Axis3 = x;
      //DirCosineAxes = {{x, x}, {x, y}, {x, z}, {y, x}, {y, y}, {y, z}, {z, x}, {z, y}, {z, z}};
      //AngVelOnOff = Off;
      //AngVelGlobal = Off;
      AnyRefFrame &rf0 = <Insert object reference (or full object definition)>;
      AnyRefFrame &rf1 = <Insert object reference (or full object definition)>;
    };

  };

Please fill the gaps yourself.

You can drive such kinematic measures in a bunch of ways. Please follow the tutorial to learn how this can be done for your particular task.

Regards,
Pavel

4

Hi Pavel,

Thank you for the reply. Based on your suggestions I made some modififications to my model, and learnt a lot, but still need some help. The new model is as follows:

T3T4Jnt as a spherical joint with added stiffness in translational directions.
BaseJnt as a six dof joint with its position and movement are fixed.

To implement FDK, I followed the SpineFixationFDK example. However, I am getting an error, “muscles are not loaded due to over constrained mechanical system”. Although, I undertand from the error message that reactions take over the function of the muscles leading to no activation, I could not find a solution. Can you help me on this please?

Ps: I have founded the error.