Browsing by Author "Van Niekerk, J. E."

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    A multibody workflow to investigate ACL biomechanics.
    (Stellenbosch : Stellenbosch University, 2019-12) Van Niekerk, J. E.; Muller, Jacobus Hendrik; Venter, Gerhard; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Anterior cruciate ligament (ACL) injury often occurs in high intensity sports involving contact or sudden changes of direction. Knee biomechanics change due to ACL injury and cause other ligaments and structures such as the medial collateral ligament (MCL) and the menisci to be at risk of concurrent injury. Presented in this study is a joint-level model of a human knee that was developed using a multibody modelling workflow and experimental data from the Open Knee(s) project. The model was developed in MSC Adams and simulated knee biomechanics between 0° and 30° of flexion for an intact and ACL deficient (ACLd) knee. Three different loading conditions were applied to the joint: (1) 100 N anterior-posterior (AP) tibial drawer, applied in 10 N increments, (2) 10 Nm varus-valgus (VV) torque, applied in 2.5 Nm increments and (3) 5 Nm internalexternal (IE) tibial torque, applied in 1 Nm increments. These loading conditions were applied individually as isolated degree of freedom loads, and simultaneously as combined degree of freedom loads. Loading conditions were applied to measure model predicted joint kinematics, ligament forces and tibiofemoral and meniscofemoral contact force. A sensitivity analysis was performed to investigate the sensitivity of modelling output to changes in modelling parameters. One parameter was changed at a time. Kinematic output was validated against experimental tibiofemoral testing data and had root mean square (RMS) errors of less than 4.50 mm for position and less than 6.5° for orientation. Predicted model outputs were the most sensitive to changes in the zero-load length (ZLL) of ligaments (> 30 % change in output parameter for 20 % change in ZLL). Changes in compliant contact stiffiness also resulted in changes in predicted output, but to a lesser extent than changes in ZLL (< 20 % change in output for 50 % change in contact stifiness). The model was least sensitive to changes in ligament stifiness (< 10 % change in output for a 30 % change in ligament stifiness). For the intact knee, the greatest force in the ACL was predicted for a combination of anterior tibial loading, valgus torque and internal tibial torque (151 N). For the ACLd knee, the model predicted that AP and IE laxity increased by 343 % and 28 % respectively when a 100 N tibial drawer load was applied. For a combination of 100 N tibial drawer load, 10 Nm valgus torque and 5 Nm internal tibial torque, AP and IE laxity increased by 261 % and 37 % respectively. ACL defiency resulted in an increase in MCL force (56 N at 30° flexion) and meniscus contact force for tibial drawer loading (33.9 N and 14.7 N at 30° flexion on the medial and lateral sides respectively). The increase in meniscus contact force coincided with joint motion that has been reported to result in meniscus injury. This study developed a multibody model of the knee using a multibody modelling approach. The model showed how anterior-posterior laxity, internalexternal tibial rotation, meniscal contact force and MCL force increased due to ACL deficiency. The model was most sensitive to changes in the ligament zero-load length and least sensitive to changes in ligament stifiness. The model confirmed previous findings describing the mechanism of meniscal ramp lesions, and the predicted meniscofemoral contact force was similar to what was measured experimentally and predicted by other models.