Analytical and computational estimation of patellofemoral forces in the knee under squatting and isometric motion

This study presents an intermediate step in prosthesis design, by introducing a newly developedtwo-dimensional mathematical, and a three-dimensional computational knee model. The analytical model isderived from Newton’s law with respect to the equilibrium equations, thus based on theoreticalassumptions, and experimentally obtained parameter. The numeric model is built from an existingprosthesis, involving three parts as patella, femur and tibia, and currently it is under development. Themodels are capable to predict – with their standard deviation – the patellofemoral (numerically tibiofemoralas well) forces in the knee joint during squatting motion. The reason why the squatting is investigated is dueto its relative simplicity and the fact, that during the movement the forces reach extremity in the knee joint.The obtained forces – as a function of flexion angle – are used firstly as fundaments to the knee designmethod, and secondly to extend the results related to the existing isometric kinetics, where one of the newlyobtained functions appears as an essential – and so far missing – input function. Most results arecompared and validated to the ones found in the relevant literature and put into a dimensionless form inorder to have more general meaning.

Effects of ACL Reconstruction Techniques on the Kinematics of the Knee in a Computational Knee Model

This study examines the effects of different Anterior Cruciate Ligament (ACL) reconstruction techniques on computational multibody knee models. The knee models were derived from two cadaver knees that underwent simulated walk cycles while the kinematics of the knee geometries were collected in a dynamic knee simulator. Once the computational models performed well compared to experimental data, multiple simulated ACL reconstruction surgeries were done on each model. For each simulated reconstruction technique, overall knee kinematics was compared to the experimental cadaver results and anterior-posterior movement of the tibia relative to the femur was compared to the original, intact computational model. The factors examined were ACL reconstruction method, adding preload to the reconstruction element, and reconstruction element type.

Multi-Body Dynamic Simulation of the Meniscus in a Computational Knee Model

The menisci have an important multifunctional role in the human knee. They protect the joint articular cartilage (by acting as a buffer between femoral and tibial surfaces while loading), provide joint lubrication, and increase joint stability (by providing congruity between femoral and tibial articular surfaces) [1]. The menisci also effectively distribute contact forces over the articular surfaces by increasing the contact surface of the joint [2].

A Three Dimensional Forward Dynamic Model of a Human Knee for Determining Ligament Forces

A three-dimensional musculoskeltal model of the human knee is being developed to investigate the forces placed on the four major knee ligaments as a result of muscle contraction. This computational knee model includes the femur, tibia, and patella, seven major muscles, four knee ligaments, and the patellar tendon. A constrained forward dynamic simulation is performed by using EMG data to estimate muscle forces. The ligament forces estimated by the model are verified by means of a robotic-cadaver experimental setup in which the knee flexion angle of a cadaver specimen was controlled by a robot. Estimated muscle forces were dynamically applied to the cadaver knee as it was flexed/extended through a specified range of motion. The ligament strain calculated by the model is compared to the strain measured experimentally and to values found in literature to verify the accuracy of the model.