Model Benchmark Summary¶
This section summarizes the steps involved in benchmarking a finite element knee model. The summary includes links to other chapters where specific details are provided.
These steps apply to the DU data set. The documentation for the OpenKnee(s) data set can be found in a separate document.
Knee Model - Initial Deviations¶
The knee model that was delivered for the Model Calibration phase will be recalibrated and used for the benchmarking phase. This step is being taken to minimize the effects of group-specific interpretation of the calibration data, where new processed experimental data was made available at the beginning of the Model Benchmarking phase. In the case of the DU specimen model that was delivered by the CSU/WSU team, the experimental kinematics will be updated and the model will be recalibrated. Specific changes are summarized below and detailed documentation is included in the Initial Deviations section.
Experimental Data¶
The only deviation that is needed from the Model Calibration phase is in the processing of the given DU kinematics. The original Model Calibration documentation misinterpreted the reported translations as joint translations rather than clinical translations. The model calibration workflow was setup to measure the joint translations from the knee model, and to avoid changing the original workflow, the experimental data will be converted from clinical translations to joint translations. Any data that is reported will specify whether clinical translations or joint translations are used. See the Initial Deviations section for more information.
Model Benchmarking¶
Experimental Data¶
The processed data delivered by the University of Denver team for benchmarking consists of anterior-posterior, varus-valgus and internal-external laxity data after anterior-cruciate ligament (ACL) resection. This data was collected at two flexion angles (roughly 15 and 55 degrees). The processed data also includes a post ACL resection passive flexion test. The recalibrated DU knee model will be used to simulate the laxity and passive flexion tests. The processed data includes what are termed “Benchmark Points”, which appear to be sampled at (or near) a succession of desired laxity loads (e.g. 80 N anterior load, etc.) from the relatively high-frequency data collected during the experiment.
The Benchmarking Points data will be used as boundary conditions in the recalibrated knee model. To reflect the resection of the ACL in the experiment, the amACL and plACL will be removed from the model. The flexion angle will be kinematically controlled and experimentally measured kinetics will be applied in all 6 degrees of freedom to the tibia’s fixed coordinate system. Model-predicted kinematics, ligament loads and contact mechanics will be recorded throughout the simulations and kinematics results will be compared to the measured values using root-mean-square (RMS) errors for each degree of freedom. For more information, see the Benchmark Simulations section.