#1




Coefficients of Spine Rhythm matrix
Hello,
I know there are several threads about spine rhythm but I have another question: all components of coefficient matrix of SpineRhythmDrv are less than 1; does it mean that T12L1 rotations are greater than other joints? Thanks, Seyedhassan Nikpour 
#2




Dear Seyedhassan,
You could think of the spine rhytm as a weight vector given to each joint to distribute the overall thoracopelvic angle. You could see that this vector is "sorted" and increasing towards T12L1  but that could be thought of as PelvisL1 < PelvisL2, PelvisL2<PelvisL3, etc. Kind regards, Pavel 
#3




Dear Pavel,
Thank you for your response. You mentioned a very good point. Actually, I am wondering if these "weights" are assigned to total rotation of each vertebra with respect to pelvis or rotation of joints (i.e. relative rotation between adjoining vertebrae). For example: Coefficient in 12th line of Coef matrix is 5.784718e001. So, does in mean: L3L4 = 5.784718e001 * T12L1 or PelvisL3 = 5.784718e001 * PelvisT12 Many Thanks, Seyedhassan 
#4




Dear Seyedhassan,
It might be or be somehow related to this number  I would need to dig into code. But I believe the easiest would be to construct a small kinematic model that is driven to flex the body and simply read out T12Pelvis vs the angle of interest. It should have a constant slop if you are using the spine rhythm. Kind regards, Pavel 
#5




spine rhythm
Dear Seyedhassan,
I have the same questions as above. Based on the code, the weight should be assigned to total rotation of each vertebra with respect to adjacent vertebra. So the result is that the T12L1 has the largest motion than other joints. It doesnot make sense. Besides, where to get the coef ? is there any reference? many thanks 
#6




Hi,
It is not correct to say that T12L1 has the largest rotation. The weight that you are looking at actually represents L1Pelvis angle as far as I remember. Unfortunately we do not have a good documentation on the spine rhythm, but the coefficients were derived from solving a beam bending problem: PDF for the spine rhythm idea Hope this helps. Regards, Pavel 
#7




Dear pgalibarov
Thanks for your reply. I am not very clear about the coef, Is it right that: if the thorax_pelvis_flexion is 20 deg. The anybody will attribute how many degress to the T12L1Jnt_flexion, L1L2Jnt_flexion,L2L3Jnt_flexion, and etc based on the coef. By the way, i want to use this coef to drive the five lumbar vertebras and want to write it into my paper. So if there is any paper discussed the coef, I can refer to it. Thanks Best regards 
#8




Yes, that is correct, but manipulating these weights is not a good idea.
If you want to get individual joint angles  you can simply exclude this spine rhythm from the analysis, and drive individual joints as you want. An example of exclusion is given in the SpineFixationWithForceDepKin example of the AMMR (check Model/Drivers.any file). Unfortunately, the spinal rhythm was not formalized into a paper. The best idea to learn kinematic rhythm is to make a small 3 segment example and see how these coefficients affect individual joint kinematics between those segments. Kind regards, Pavel 
#9




The angle of joint in lumbar
Hi
I caculated the matrix of axes of L4_seg with respect to the matrix of the axes of L5_seg. Then, transfered the result of matrix into Euler angle, and found that the Euler angle was the exactly the same with Jnt45.Pos. So the Jnt45.Pos represents the sagittal,coronal,horizontal angle with respect to adjacet segment. However, the angle, JntT12L1.Pos>JntL1L2.Pos>JntL2L3.Pos>JntL3L4.Pos>J ntL4L5.Pos>JntL5Scram.Pos. And this result is consistent with the explanation of the coeff of spinerhythm. However, this result is totally unacceptable. it dosenot make sensor at all. 
#10




Hello,
As i mentioned before, the spine rhythm coefficients were derived from the beam theory equations. But in reality these coefficients will be dependent on the joint and corresponding ligament stiffness. So a stiffer joint, e.g. with pathology, would allow less motion in the spinal unit, whereas a more elastic one will be moving more. Unfortunately it is difficult to calibrate the discs, so by default these values are used. So it represents a single person with the stiffness increasing towards the sacrum, and it does make sense in this particular case, because it was defined like that. If you provide your values you could use SpineFixationWithForceDepKinematics model to define subjectspecific values. Please have a look at the abstract that describes how this behaviour could be changed: ON MODELLING SPINE CURVATURE Regards, Pavel 
Tags 
anykinmeasurelincomb, lumber, rhythm, rotation, shperical joints 
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