Conference Paper

Evaluation of laxity tests with a musculoskeletal model of Total Knee Arthroplasty.

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We hypothesized changes in rotations and translations after TKA with a fixed-bearing anterior cruciate ligament (ACL)-sacrificing but posterior cruciate ligament (PCL)-retaining design with equal-sized, circular femoral condyles would reflect the changes of articular geometry. Using 8 cadaveric knees, we compared the kinematics of normal knees and TKA in a standardized navigated position with defined loads. The quadriceps was tensed and moments and drawer forces applied during knee flexion-extension while recording the kinematics with the navigation system. TKA caused loss of the screw-home; the flexed tibia remained at the externally rotated position of normal full knee extension with considerably increased external rotation from 63 degrees to 11 degrees extension. The range of internal-external rotation was shifted externally from 30 degrees to 20 degrees extension. There was a small tibial posterior translation from 40 degrees to 90 degrees flexion. The varus-valgus alignment and laxity did not change after TKA. Thus, navigated TKA provided good coronal plane alignment but still lost some aspects of physiologic motion. The loss of tibial screw-home was related to the symmetric femoral condyles, but the posterior translation in flexion was opposite the expected change after TKA with the PCL intact and the ACL excised. Thus, the data confirmed our hypothesis for rotations but not for translations. It is not known whether the standard navigated position provides the best match to physiologic kinematics.
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The experimental study of joint kinematics in three dimensions requires the description and measurement of six motion components. An important aspect of any method of description is the ease with which it is communicated to those who use the data. This paper presents a joint coordinate system that provides a simple geometric description of the three-dimensional rotational and translational motion between two rigid bodies. The coordinate system is applied to the knee and related to the commonly used clinical terms for knee joint motion. A convenient characteristic of the coordinate system shared by spatial linkages is that large joint displacements are independent of the order in which the component translations and rotations occur.
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Musculoskeletal (MS) models should be able to integrate the patient-specific MS architecture and undergo thorough validation prior to their introduction into the clinical practice. We present a streamlined methodology to develop subject-specific models able to simultaneously predict body-level dynamics, muscle forces, ligament forces, knee joint contact forces and secondary knee kinematics. The MS architecture of a generic cadaver-based model was scaled using an advanced morphing technique to the subject-specific morphology of a patient implanted with an instrumented total knee arthroplasty available in the fifth "Grand Challenge Competition to Predict in Vivo Knee Loads" dataset. Inverse dynamics-like analyses of a hinge-like knee model and an 11-degree-of-freedom force-dependent kinematics (FDK) knee model were simulated for one gait, one right-turn and one unloaded leg-swing trial. Predicted tibiofemoral (TF) forces and secondary knee kinematics were evaluated using experimental data available in the Grand Challenge dataset. Total TF contact forces were predicted with a root-mean-square error (RMSE) and a coefficient of determination (R^2) smaller than 0.3 BW and higher than 0.9, respectively, for both gait and right-turn trials. Secondary knee kinematics from the leg-swing trial were overall better approximated using the FDK model (average Sprague and Geers' combined error C = 0.06) than when using a hinged knee model (C = 0.34). The proposed modeling approach allows detailed subject-specific scaling and personalization, and does not contain any non-physiological parameters. This modeling framework has potential applications in aiding the clinical decision-making in orthopedics procedures, and as a tool for virtual implant design.
Force-dependent kinematics: a new analysis method for nonconforming joints
  • M S Andersen
  • M Damsgaard
  • J Rasmussen
M. S. Andersen, M. Damsgaard, and J. Rasmussen, "Force-dependent kinematics: a new analysis method for nonconforming joints," in XIII International Symposium on Computer Simulation in Biomechanics, 2011.