simtk.org

Greetings everyone,

I would like to ask a question about the name conventions in the provided kinematics data (tdms files). From what I have seen in the specifications, the data are recorded with the tibia fixed and the femur free. If that is indeed the case, then the 'Posterior Translation" channel stores the data for the translation of the femur. Do the positive values imply that the femur moves towards the negative anterior posterior axis of the femoral coordinate system (assuming that the anterior direction is towards the knee frontal plane)?

Thanks in advance,
Konstantinos,
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Konstantinos Risvas
Dipl.-Ing. MSc Electrical and Computer Engineer
Research Associate, VVR group
Department of Electrical and Computer Engineering
University of Patras
26500, Rio-Patras, Greece

Dear Kostas,

During experimentation of the tibiofemoral joint, the tibia was indeed fixed. Yet, the reporting of joint kinematics is for posterior translation of tibia. See https://simtk.org/plugins/moinmoin/open ... ystems.pdf for more details.

For a sister project (https://simtk.org/projects/kneehub), we processed the tibiofemoral joint mechanics data for one of the knees to report in a more usable form. Our data processing steps are described in a document at the source code repository (https://simtk.org/svn/openknee/app/Knee ... Knees.docx) That may be helpful as well.

Ahmet

Dear Dr Erdemir,

Thanks a lot for your prompt answer and the provided links.

Kind regards,
Kostas

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Konstantinos Risvas
Dipl.-Ing. MSc Electrical and Computer Engineer
Research Associate, VVR group
Department of Electrical and Computer Engineering
University of Patras
26500, Rio-Patras, Greece

Greetings again,

I have one more question. Navigating through the kinematics data provided, I noticed that for some subjects there are multiple passive flexion records (e.g oks008). I guess this is for optimizing the femoral coordinate system as it is described in the readme.txt. I would like to ask if it is recommended to use the last set of these records and if the subsequent motions (eg ALL laxity) are recorded based upon this last optimized passive flexion motion.

Kind regards,
Konstantinos

Dear Kostas,

First of all, each kinematics-kinetics data folder should have a state file (within the zipped vproj file as I recall) that has all the coordinate system transformations, e.g. between anatomical, optimized, tibia, femur, robot, optotrak, etc. That state file corresponds to that motion, in many cases it is the same for all trial folders but sometimes, we needed to regenerate coordinate systems.

Usually, passive flexion test is done to calculate an optimized coordinate system, i.e. femur axis is oriented to minimize out of plane rotations, tibia remains the same. In subsequent tests, that dictates around which axis flexion is prescribed. Note that this doesn't affect loading as they are applied in the tibia crd. sys. Please also note that the tdms files represents kinematics and kinetics data in various coordinate systems for convenience, anatomical, optimized, etc.

Cheers,
ahm.