Customized surface-guided knee implant: Contact analysis and experimental test

2017 ◽  
Vol 232 (1) ◽  
pp. 90-100 ◽  
Author(s):  
Ida Khosravipour ◽  
Shabnam Pejhan ◽  
Yunhua Luo ◽  
Urs P Wyss
Keyword(s):  
Molecular Weight ◽  
Finite Element ◽  
High Molecular Weight ◽  
Contact Pressure ◽  
Element Analysis ◽  
Pressure Sensitive ◽  
Sensitive Film ◽  
Pressure Sensitive Film ◽  
Total Knee ◽  
Ultra High Molecular Weight

Contact pressure and stresses on the articulating surface of the tibial component of a total knee replacement are directly related to the joint contact forces and the contact area. These stresses can result in wear and fatigue damage of the ultra-high-molecular-weight polyethylene. Therefore, conducting stress analysis on a newly designed surface-guided knee implant is necessary to evaluate the design with respect to the polyethylene wear. Finite element modeling is used to analyze the design’s performance in level walking, stair ascending and squatting. Two different constitutive material models have been used for the tibia component to evaluate the effect of material properties on the stress distribution. The contact pressure results of the finite element analysis are compared with the results of contact pressure using pressure-sensitive film tests. In both analyses, the average contact pressure remains below the material limits of ultra-high-molecular-weight polyethylene insert. The peak von Mises stresses in 90° of flexion and 120° of flexion (squatting) are 16.28 and 29.55 MPa, respectively. All the peak stresses are less than the fatigue failure limit of ultra-high-molecular-weight polyethylene which is 32 MPa. The average contact pressure during 90° and 120° of flexion in squatting are 5.51 and 5.46 MPa according to finite element analysis and 5.67 and 8.14 MPa according to pressure-sensitive film experiment. Surface-guided knee implants are aimed to resolve the limitations in activities of daily living after total knee replacement by providing close to normal kinematics. The proposed knee implant model provides patterns of motion much closer to the natural target, especially as the knee flexes to higher degrees during squatting.

Finite Element Model of Equal Channel Angular Extrusion of Ultra High Molecular Weight Polyethylene

2021 ◽  
pp. 1-30
Author(s):  
Kostiantyn Vasylevskyi ◽  
Igor Tsukrov ◽  
Kateryna Miroshnichenko ◽  
Stanislav Buklovskyi ◽  
Hannah Grover ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Finite Element ◽  
Shear Strain ◽  
High Molecular Weight ◽  
Equal Channel Angular Extrusion ◽  
Dead Zone ◽  
Extrusion Force ◽  
Element Analysis ◽  
Angular Extrusion ◽  
Ultra High Molecular Weight

Abstract Ultra-high molecular weight polyethylene (UHMWPE) used in biomedical applications, e.g. as a bearing surface in total joint arthroplasty, has to possess superior tribological properties, high mechanical strength, and toughness. Recently, equal channel angular extrusion (ECAE) was proposed as a processing method to introduce large shear strains to achieve higher molecular entanglement and superior mechanical properties of this material. Finite element analysis (FEA) can be utilized to evaluate the influence of important manufacturing parameters such as the extrusion rate, temperature, geometry of the die, back pressure, and friction effects. In this paper we present efficient FEA models of ECAE for UHMWPE. Our studies demonstrate that the choice of the constitutive model is extremely important for the accuracy of numerical modeling predictions. Three considered material models (J2-plasticity, Bergstrom-Boyce, and the Three Network Model) predict different extrusion loads, deformed shapes and accumulated shear strain distributions. The work has also shown that the friction coefficient significantly influences the punch force and that the 2D plane strain assumption can become inaccurate in the presence of friction between the billet and the extrusion channel. Additionally, a sharp corner in the die can lead to the formation of the so-called “dead zone” due to a portion of the material lodging into the corner and separating from the billet. Our study shows that the presence of this material in the corner substantially affects the extrusion force and the resulting distribution of accumulated shear strain within the billet

The Wear of UHMWPE in Total Knee Replacements: Experimental and Finite Element Analysis of Contact Behaviour

2001 ◽  
Author(s):  
Dorothy M. Murphy ◽  
Alan Kavanagh ◽  
Tim M. McGloughlin
Keyword(s):  
Molecular Weight ◽  
Finite Element Analysis ◽  
Element Analysis ◽  
Total Knee Replacements ◽  
Total Hip Replacements ◽  
Contact Behaviour ◽  
Knee Replacements ◽  
Hip Replacements ◽  
Total Knee ◽  
Ultra High Molecular Weight

Abstract Upon examination of failed total knee replacements, it has been concluded that it is the performance of the ultra high molecular weight polyethylene (UHMWPE) tibial component that governs the useful lifespan of such a joint. Severe wear of UHMWPE is associated more with tibial components of the knee than with the acetabular cups of total hip replacements. This is due to a notable lack of congruity between the articulating surfaces which leads to the presence of significant localised stresses in the femoro-tibial interface.

Contact Stress and Linearized Modal Predictions of As-Built Preloaded Assembly

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Adam R. Brink ◽  
Robert J. Kuether ◽  
Matthew D. Fronk ◽  
Bryan L. Witt ◽  
Brendan L. Nation
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Contact Area ◽  
Element Model ◽  
High Fidelity ◽  
Vibration Modes ◽  
Low Level ◽  
Pressure Sensitive ◽  
Sensitive Film ◽  
Pressure Sensitive Film

Abstract The member stiffness and pressure distribution in a bolted joint is significantly influenced by the contact area of the mechanical interface under a prescribed preload force. This research explores the influence of as-built surface profiles for nominally flat interfaces of a C-Beam assembly with two well-defined contact regions. A high-fidelity finite element model is created such that the model uncertainty is minimized by updating and calibrating the piece parts prior to the preload assembly procedure. The model is then assembled and preloaded to evaluate the contact stresses and contact area for both nominally flat and perturbed non-flat surfaces based on three-dimensional surface topography measurements. The predicted pressures are validated with digitized pressure-sensitive film measurements. The high-fidelity modeling reveals how the compliance and thickness of the pressure-sensitive film alter the measured pressures, leading to incorrect evaluations of the stresses and contact area in the joint. The resulting low-level dynamic behavior of the preloaded assembly is shown to be sensitive to the true contact area by linearizing the nonlinear finite element model about the preloaded equilibrium and performing a computational modal analysis. The resonant frequencies are validated with experimental measurements to demonstrate the effect of the contact area on the modal characteristics of the bolted assembly. Vibration modes and loading patterns exhibit varying levels of sensitivity to the contact area in the joint, leading to an improved physical understanding of the influence of contact mechanics on the low-level linear vibration modes of jointed assemblies.

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