Posterior cruciate ligament balancing in total knee arthroplasty: a numerical study with a dynamic force controlled knee model

Background: Adequate soft tissue balancing is a key factor for a successful result after total knee arthroplasty (TKA). Posterior cruciate ligament (PCL) is the primary restraint to posterior translation of the tibia after cruciate retaining TKA and is also responsible for the amount of joint compression. However, it is complex to quantify the amount of ligament release with its effects on load bearing and kinematics in TKA and limited both in vivo and in vitro. The goal of this study was to create a dynamic and deformable finite element model of a full leg and analyze a stepwise release of the PCL regarding knee kinematics, pressure distribution and ligament stresses. Methods: A dynamic finite element model was developed in Ansys V14.0 based on boundary conditions of an existing knee rig. A cruciate retraining knee prosthesis was virtually implanted. Ligament and muscle structures were simulated with modified spring elements. Linear elastic materials were defined for femoral component, inlay and patella cartilage. A restart algorithm was developed and implemented into the finite element simulation to hold the ground reaction force constant by adapting quadriceps force. After simulating the unreleased PCL model, two models were developed and calculated with the same boundary conditions with a 50% and 75% release of the PCL stiffness. Results: From the beginning of the simulation to approximately 35 degrees of flexion, tibia moves posterior related to the femur and with higher flexion anteriorly. Anterior translation of the tibia ranged from 5.8 mm for unreleased PCL to 3.7 mm for 75% PCL release (4.9 mm 50% release). A decrease of maximum von Mises equivalent stress on the inlay was given with PCL release, especially in higher flexion angles from 11.1 MPa for unreleased PCL to 8.9 MPa for 50% release of the PCL and 7.8 MPa for 75% release. Conclusions: Our study showed that dynamic FEM is an effective method for simulation of PCL balancing in knee arthroplasty. A tight PCL led in silico to more anterior tibia translation, a higher collateral ligament and inlay stress, while retropatellar pressure remained unchanged. Surgeons may take these results in vivo into account

PMMA Third-Body Wear after Unicondylar Knee Arthroplasty Decuples the UHMWPE Wear Particle Generation In Vitro

Introduction. Overlooked polymethylmethacrylate after unicondylar knee arthroplasty can be a potential problem, since this might influence the generated wear particle size and morphology. The aim of this study was the analysis of polyethylene wear in a knee wear simulator for changes in size, morphology, and particle number after the addition of third-bodies. Material and Methods. Fixed bearing unicondylar knee prostheses (UKA) were tested in a knee simulator for 5.0 million cycles. Following bone particles were added for 1.5million cycles, followed by 1.5million cycles with PMMA particles. A particle analysis by scanning electron microscopy of the lubricant after the cycles was performed. Size and morphology of the generated wear were characterized. Further, the number of particles per 1 million cycles was calculated for each group. Results. The particles of all groups were similar in size and shape. The number of particles in the PMMA group showed 10-fold higher values than in the bone and control group (PMMA: 10.251 x 10(12); bone: 1.145x10(12); control: 1.804x10(12)). Conclusion. The addition of bone or PMMA particles in terms of a third-body wear results in no change of particle size and morphology. PMMA third-bodies generated tenfold elevated particle numbers. This could favor an early aseptic loosening

Calculation of the elastic properties of prosthetic knee components with an iterative finite element-based modal analysis: quantitative comparison of different measuring techniques.

With the aging but still active population, research on total joint replacements relies increasingly on numerical methods, such as finite element analysis, to improve wear resistance of components. However, the validity of finite element models largely depends on the accuracy of their material behavior and geometrical representation. In particular, material properties are often based on manufacturer data or literature reports, but can alternatively be estimated by matching experimental measurements and structural predictions through modal analyses and identification of eigenfrequencies. The aim of the present study was to compare the accuracy of common setups used for estimating the eigenfrequencies of typical components often used in prosthetized joints. Eigenfrequencies of cobalt-chrome and ultra-high-molecular weight polyethylene components were therefore measured with four different setups, and used in modal analyses of corresponding finite element models for an iterative adjustment of their material properties. Results show that for the low-damped cobalt chromium endoprosthesis components, all common measuring setups provided accurate measurements. In the case of high-damped structures, measurements were only possible with setups including a continuously excitation system such as electrodynamic shakers. This study demonstrates that the iterative back-calculation of eigenfrequencies can be a reliable method to estimate the elastic properties for finite element models

Rapid Prototyping for In Vitro Knee Rig Investigations of Prosthetized Knee Biomechanics: Comparison with Cobalt-Chromium Alloy Implant Material

Retropatellar complications after total knee arthroplasty (TKA) such as anterior knee pain and subluxations might be related to altered patellofemoral biomechanics, in particular to trochlear design and femorotibial joint positioning. A method was developed to test femorotibial and patellofemoral joint modifications separately with 3D-rapid prototyped components for in vitro tests, but material differences may further influence results. This pilot study aims at validating the use of prostheses made of photopolymerized rapid prototype material (RPM) by measuring the sliding friction with a ring-on-disc setup as well as knee kinematics and retropatellar pressure on a knee rig. Cobalt-chromium alloy (standard prosthesis material, SPM) prostheses served as validation standard. Friction coefficients between these materials and polytetrafluoroethylene (PTFE) were additionally tested as this latter material is commonly used to protect pressure sensors in experiments. No statistical differences were found between friction coefficients of both materials to PTFE. UHMWPE shows higher friction coefficient at low axial loads for RPM, a difference that disappears at higher load. No measurable statistical differences were found in knee kinematics and retropatellar pressure distribution. This suggests that using polymer prototypes may be a valid alternative to original components for in vitro TKA studies and future investigations on knee biomechanics

Increase in the Tibial Slope Reduces Wear after Medial Unicompartmental Fixed-Bearing Arthroplasty of the Knee

Introduction. Unicompartmental arthroplasty of the knee in patients with isolated medial osteoarthritis gives good results, but survival is inferior to that of total knee prosthesis. Knees may fail because positioning of the prosthesis has been suboptimal. The aim of this study was to investigate the influence of the tibial slope on the rate of wear of amedial fixed-bearing unicompartmental knee arthroplasty. Materials and Methods. We simulated wear on a medial fixed-bearing unicompartmental knee prosthesis (Univation) in vitro with a customised, four-station, and servohydraulic knee wear simulator, which exactly reproduced the walking cycle (International Organisation for Standardisation (ISO) 14243-1: 2002(E)). The medial prostheses were inserted with 3 different posterior tibial slopes: 0 degrees, 4 degrees, and 8 degrees (n = 3 in each group). Results. The wear rate decreased significantly between 0 degrees and 4 degrees slope from 10.4 (SD 0.62) mg/million cycles to 3.22 (SD 1.71) mg/million cycles. Increasing the tibial slope to 8 degrees did not significantly change the wear rate. Discussion. As an increase in the tibial slope reduced the wear rate in a fixed-bearing prosthesis, a higher tibial slope should be recommended. However, other factors that are influenced by the tibial slope (e.g.,the tension of the ligament) must also be considered

Increase in the Tibial Slope Reduces Wear after Medial Unicompartmental Fixed-Bearing Arthroplasty of the Knee

Introduction. Unicompartmental arthroplasty of the knee in patients with isolated medial osteoarthritis gives good results, but survival is inferior to that of total knee prosthesis. Knees may fail because positioning of the prosthesis has been suboptimal. The aim of this study was to investigate the influence of the tibial slope on the rate of wear of amedial fixed-bearing unicompartmental knee arthroplasty. Materials and Methods. We simulated wear on a medial fixed-bearing unicompartmental knee prosthesis (Univation) in vitro with a customised, four-station, and servohydraulic knee wear simulator, which exactly reproduced the walking cycle (International Organisation for Standardisation (ISO) 14243-1: 2002(E)). The medial prostheses were inserted with 3 different posterior tibial slopes: 0 degrees, 4 degrees, and 8 degrees (n = 3 in each group). Results. The wear rate decreased significantly between 0 degrees and 4 degrees slope from 10.4 (SD 0.62) mg/million cycles to 3.22 (SD 1.71) mg/million cycles. Increasing the tibial slope to 8 degrees did not significantly change the wear rate. Discussion. As an increase in the tibial slope reduced the wear rate in a fixed-bearing prosthesis, a higher tibial slope should be recommended. However, other factors that are influenced by the tibial slope (e.g.,the tension of the ligament) must also be considered

Classification of Chemicals According to UN-GHS and EU-CLP: A Review of Physical Hazard Classes and Their Intricate Interfaces to Transport and Former EU Legislation

The Globally Harmonized System of Classification and Labelling of Chemicals (UN-GHS) is being implemented in more and more countries all over the world; the EU has done so with the CLP-Regulation (EU-CLP). Compared to the undeniably important questions on health and environmental hazards, the classification of physical hazards of chemicals often has not been in the focus, although their implementation can be challenging and there are traps and pitfalls to be avoided. The following overview of the classification systematics for physical hazards aims at a principle understanding without detailing all criteria or test methods. Similarities and differences between the classification systems of the UN-GHS and EU-CLP, the transport of dangerous goods and the former EU system are reviewed with regard to the physical hazard classes. Available physical hazard classifications for the transport of dangerous goods and according to the former EU system can be used as available information when classifying according to the GHS. However, the interfaces of these classification systems and their limitations have to be understood well when concluding on GHS/CLP classifications. This applies not only to industry when applying CLP but especially to legislators when adapting legislation that in one way or another refers to the classification of chemicals

Increase in the Tibial Slope in Unicondylar Knee Replacement: Analysis of the Effect on the Kinematics and Ligaments in a Weight-Bearing Finite Element Model

Introduction. Unicompartmental arthroplasty (UKA) of the knee in patients with isolated medial osteoarthritis yields adequate results;however, the survival rate is inferior to that of total knee arthroplasty (TKA). A key factor in the longevity of the implant is the positioning;however, the optimal tibial slope in UKA has not been determined. The aim of this study was to establish a finite element (FE) model and investigate the effect of the tibial slope on the strain of the ligaments, kinematics, inlay movement, and load in the nonreplaced patellofemoral compartment in a medial mobile bearing UKA. Materials and Methods. An FE model of a leg was established with a virtual UKA implantation with three different tibial slopes (0 degrees, 5 degrees, and 10 degrees). Subsequently, the knee was flexed from 14-73 degrees. In addition, the ground reaction force and the muscles were simulated. Results. With a higher tibial slope, there was more external rotation of the tibia. An increased tibial slope provided a lateral shift of the patella in the trochlear groove and a more anterior position of the inlay. The ligament strains were also changed, specifically, the anterior portion of the medial collateral ligament and the posterior cruciate ligament (PCL). Discussion. This study established the first model of a quasidynamic mobile bearing UKA in a leg under weight-bearing conditions. With an increasing tibial slope, there was a higher external rotation of the tibia that created different femorotibial and retropatellar kinematics and different strains in the ligaments. This knowledge adds important information for the optimal tibial slope that has to be determined individually depending on the patient's preoperative kinematics, desired postoperative kinematics, ligament status, and location of the retropatellar chondral damage

Global data on earthworm abundance, biomass, diversity and corresponding environmental properties

Publisher Copyright: © 2021, The Author(s).Earthworms are an important soil taxon as ecosystem engineers, providing a variety of crucial ecosystem functions and services. Little is known about their diversity and distribution at large spatial scales, despite the availability of considerable amounts of local-scale data. Earthworm diversity data, obtained from the primary literature or provided directly by authors, were collated with information on site locations, including coordinates, habitat cover, and soil properties. Datasets were required, at a minimum, to include abundance or biomass of earthworms at a site. Where possible, site-level species lists were included, as well as the abundance and biomass of individual species and ecological groups. This global dataset contains 10,840 sites, with 184 species, from 60 countries and all continents except Antarctica. The data were obtained from 182 published articles, published between 1973 and 2017, and 17 unpublished datasets. Amalgamating data into a single global database will assist researchers in investigating and answering a wide variety of pressing questions, for example, jointly assessing aboveground and belowground biodiversity distributions and drivers of biodiversity change.Peer reviewe