Extract Experimental Data

The OpenKnee(s) experimentally measured kinematics and kinetics are reported in .tdms files. These files contain three sets of data that are used in model calibration.

  1. Kinetics.JCS.Desired, The kinetics that were specified for the test case.
  2. State.JCS Load , The joint kinetics that are measured during the test case. These loads are taken to be reported with respect to the fixed tibial coordinate system. The following is from the OpenKnee(s) documentation This is the kinetic state of the joint (i.e. tibia loads). More specifically, it is the joint (tibia) loads that are ... This can be found on page 8 of this document: https://simtk.org/plugins/moinmoin/openknee/Infrastructure/ExperimentationMechanics?action=AttachFile&do=get&target=2013CB-031-002.B+simVITRO+Data+File+Contents_Open+Knee.pdf
  3. State.JCS, The measured joint kinematics derived from the robot position and defined using the optimized femur coordinate system.

These data are time-synced, and it is assumed that the values at each given index correspond to the other reported values at the same index. During preprocessing for model calibration, the indicies of the desired points in the experimental test case are defined, and these indicies are later used to extract specific kinematics and kinetics from the .tdms file.

The specified (Kinetics.JCS.Desired) kinetics are used to parse the experimental data. The specified data ramps the load up by a certain amount, then holds the load for a time before ramping to the next specified load. A custom program (Fig. 2) is used to select the data at the end of a “hold” step (Fig. 3). This program is used to plot the specified kinetics for the load cases that are reported in the .tdms file. The user then selects the range that is desired, and custom python scripts are used to select the points at the end of each ramp’s “hold” step (Fig. 3). The indicies of the selected points are recorded in a .xml file, along with metadata, including the specimen number, name assigned to the test case, and the .tdms file that was used to extract the data. The recorded indicies are later used to extract the experimentally joint kinematics and kinetics from the .tdms file.

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Fig. 2 The GUI of the the semi-automatic process of extracting experimental data.

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Fig. 3 A larger view of the last five selected steps in the anterior drawer test at \(0^\circ\) flexion. Note the red line shows the specified joint kinetics (Kinetics.JCS.Desired), and the green line shows the experimentally measured kinetics (State.JCS Load).