# Motion segment of the spine

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.

Can anybody help me on this please?

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)>;
};

};
``````

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

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.