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W pracy zaprezentowano możliwości stosowania nowoczesnych metod inżynierskich w planowaniu zabiegu operacyjnego całkowitej wymiany stawu kolanowego. Został omówiony proces wykonywania wirtualnych i fizycznych modeli stawu kolanowego przy użyciu metod inżynierii odwrotnej. Obiektem wejściowym do realizacji procesu były obrazy DICOM, które pochodziły z badania tomograficznego. Przedstawiono także potencjalne korzyści wynikające z użycia tych technik.
The paper presents the possibility of using modern engineering methods in planning total knee replacement surgery. It was discussed the process of making virtual and physical knee models using methods of reverse engineering. The input object for the process were DICOM images that came from a computed tomography scan. The potential benefits of using these techniques were also presented.
Content available remote Construction-conditioned rollback in total knee replacement: fluoroscopic results
Firstly, the way of implementing approximatively the initial rollback of the natural tibiofemoral joint (TFJ) in a total knee replacement (AEQUOS G1 TKR) is discussed. By configuration of the curvatures of the medial and lateral articulating surfaces a cam gear mechanism with positive drive can be installed, which works under force closure of the femoral and tibial surfaces. Briefly the geometric design features in flexion/extension are described and construction-conditioned kinematical and functional properties that arise are discussed. Due to a positive drive of the cam gear under the force closure during the stance phase of gait the articulating surfaces predominantly roll. As a result of rolling, a sliding friction is avoided, thus the resistance to motion is reduced during the stance phase. Secondly, in vivo fluoroscopic measurements of the patella tendon angle during flexion/extension are presented. The patella tendon angle/ knee flexion angle characteristic and the kinematic profile in trend were similar to those observed in the native knee during gait (0°–60°).
Malalignment of Total Knee Replacement prosthesis has been reported to limit the implant survival time. We hypothesized that this may be secondary to excessive stress occurring at the bone-implant interface, resulting from abnormal load transfer across the knee joint. In this study, we conducted Finite Element Analysis of a geometrical model of the knee joint after Total Knee Replacement with different axial alignments. The calculated stresses and displacements were significantly higher with varus knee malalignment than with the valgus one. The stresses are not high enough to pose a serious risk of a crack or a fracture but might be responsible for chronic pain reported by some patients. In cases where optimal implant positioning is not possible, slight valgus malalignment might produce better results than varus.
The purposes of the paper were as follows: to show the fundamental functional differences between the natural knee and common total knee replacements (TKR), to describe the ideas on how main properties of the natural knee can be adopted by a novel TKR and to present some main biomechanical functions of this TKR. By analyzing the morphology of the articulating surfaces and the kinematics of the natural knee the design of the novel TKR was developed. The use was made of the test procedures established in vitro and of lateral X-ray photographs as well as fluoroscopy in vivo. The function of the novel TKR is comparable to that of the natural knee joint in terms of kinematics (roll/slide behaviour), loads of the articulating surfaces (diminished shear loads), stability and leeway under external impacts, reduction of the load in the patellofemoral joint, and ligament balancing.
In the present work, a wear evaluation of the UHMWPE tibial insert of a total knee joint is attempted based on a simple wear model. A user subroutine has been written and integrated into a commercial finite element program to allow for a structural-kinematic model of the joint. The kinematic model simulates the relative angular velocity and linear movements between tibia and femur during walking. The input data consist of internal-external rotation and flexion-extension angle as taken from the literature. In the simulation, the femoral and tibial components are compressed vertically under gait loads, while at different orientations as determined by the kinematic model. A stress history of each element during the gait cycle is determined. The calculation of the product between the contact pressure and the node relative velocity, as given by the kinematic model, is then used for a qualitative determination of wear maps.
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