Editorial

Extracting clinically relevant data from finite element simulations

Plusieurs études ont démontré la relation entre les douleurs fémoropatellaires et l’insatisfaction du patient après implantation d’une prothèse totale de genou (PTG). Peu de simulations numériques en éléments finis permettent une évaluation fémoropatellaire tout au long de la flexion. Le but de cette étude était de valider un nouveau modèle numérique piloté en forces et moments et analysant les efforts fémoropatellaires après PTG lors d’un squat.

Notre simulation numérique d’un squat par une modélisation pilotée en efforts et moments est comparable aux données expérimentales et numériques de la littérature.

Nous avons développé une modélisation du membre inférieur en éléments finis avec implantation d’une PTG postéro-stabilisée à plateau fixe. Afin de simuler les conditions mécaniques d’un squat en appui bipodal, une force imposée de 130 N était appliquée au centre du genou prothétique. Les efforts appliqués au tendon quadricipital, les pressions de contact et les contraintes de Von Mises observés sur l’implant patellaire, les efforts et leur répartition sur l’insert tibial, ainsi que la mise en contact du système plot-came étaient évalués jusqu’à 100° de flexion.

Les efforts appliqués au tendon quadricipital augmentaient au cours de la flexion jusqu’à 6 fois la force imposée. Les contraintes Von Mises à la surface de l’implant patellaire augmentaient jusqu’à 16 MPa à 100° de flexion. Les efforts de contact fémorotibial augmentaient pour atteindre 415N en médial et 339N en latéral, avec une répartition sur l’insert tibial de 64 % en médial versus 36 % en latéral. L’angle de flexion correspondant au début du contact du système plot-came était de l’ordre de 70°.

Dans notre simulation, les efforts de contact fémorotibiaux et fémoropatellaire, leur répartition entre compartiment médial et latéral, ainsi que la mise en contact du système plot-came étaient compatibles avec de nombreux travaux publiés. Ces résultats de validation suggèrent que la simulation d’un squat peut être pilotée en efforts et moments afin de reproduire facilement les conditions passives retrouvées lors de la flexion d’un genou prothétique, sans intégration de données cinématiques expérimentales au préalable.

Cette étude représente une première étape de validation des comportements mécaniques fémorotibial et fémoropatellaire issus de cette simulation numérique de squat, pilotée en efforts et moments, après implantation d’une prothèse totale de genou postéro-stabilisée. Ce modèle permettrait une meilleure compréhension des efforts fémoropatellaires en rapport avec les différentes techniques d’implantation prothétique.

Niveau de Preuve: IV ; Etude biomécanique numérique.

Several studies have documented the relationship between patellofemoral pain and patient dissatisfaction after total knee arthroplasty (TKA). However, few computer simulations have been designed to evaluate the patellofemoral joint during flexion. The aim of this study was to validate a new computational simulation, driven by forces and moments, and to analyze patellofemoral reaction forces and stress under squat loading conditions after TKA implantation.

This computational simulation of a squat using a model driven by forces and moments is comparable to in vitro and in silico data from the literature.

We developed a finite element model of the lower limb after implantation of a fixed-bearing posterior-stabilized TKA. To simulate squat loading conditions when standing on both legs, an initial load of 130 N was applied to the center of the femoral head. Quadriceps force, patellofemoral contact force and Von Mises stress on the patellar implant, tibiofemoral contact forces and pressure on the tibial insert, and post-cam contact force were evaluated from 0° to 100° of knee flexion.

Quadriceps force increased during flexion, up to 6 times the applied load. Von Mises stress on patellar implant increased up to 16 MPa at 100° flexion. Tibiofemoral contact forces increased up to 415 N medially and 339 N laterally, with 64% distributed medially on the tibial insert. Post-cam contact started slightly before 70° of flexion.

In this simulation, tibiofemoral, patellofemoral and post-cam contact forces, and pressure distribution on the tibial insert were consistent with various published studies. This agreement suggests that computational simulation driven by forces and moments can reproduce squat loading conditions during knee flexion after TKA, without experimental kinematic data used to drive the simulation.

This study represents an initial step towards validating tibiofemoral and patellofemoral mechanical behavior under squat conditions, from this computational simulation driven by forces and moments. This model will help us better understand the influence of various implantation techniques on patellofemoral forces and stress during flexion.

IV, biomechanical computational study.

Biomechanical simulation of the foot and ankle complex is a growing research area but compared to simulation of joints such as hip and knee, it has been under investigated and lacks consistency in research methodology. The methodology is variable, data is heterogenous and there are no clear output criteria. Therefore, it is very difficult to correlate clinically and draw meaningful inferences.

The focus of this review is finite element simulation of the native ankle joint and we will explore: the different research questions asked, the model designs used, ways the model rigour has been ensured, the different output parameters of interest and the clinical impact and relevance of these studies.

The 72 published studies explored in this review demonstrate wide variability in approach. Many studies demonstrated a preference for simplicity when representing different tissues, with the majority using linear isotropic material properties to represent the bone, cartilage and ligaments; this allows the models to be complex in another way such as to include more bones or complex loading. Most studies were validated against experimental or in vivo data, but a large proportion (40%) of studies were not validated at all, which is an area of concern.

Finite element simulation of the ankle shows promise as a clinical tool for improving outcomes. Standardisation of model creation and standardisation of reporting would increase trust, and enable independent validation, through which successful clinical application of the research could be realised.

To discuss the state of the art of Finite Element (FE) modeling in implant dentistry, to highlight the principal features and the current limitations, and giving recommendations to pave the way for future studies.

The articles’ search was performed through PubMed, Web of Science, Scopus, Science Direct, and Google Scholar using specific keywords. The articles were selected based on the inclusion and exclusion criteria, after title, abstract and full-text evaluation. A total of 147 studies were included in this review.

To date, the FE analysis of the bone-dental implant system has been investigated by analyzing several types of implants; modeling only a portion of bone considered as isotropic material, despite its anisotropic behavior; assuming in most cases complete osseointegration; considering compressive or oblique forces acting on the implant; neglecting muscle forces and the bone remodeling process. Finally, there is no standardized approach for FE modeling in the dentistry field.

FE modeling is an effective computational tool to investigate the long-term stability of implants. The ultimate aim is to transfer such technology into clinical practice to help dentists in the diagnostic and therapeutic phases. To do this, future research should deeply investigate the loading influence on the bone-implant complex at a microscale level. This is a key factor still not adequately studied. Thus, a multiscale model could be useful, allowing to account for this information through multiple length scales. It could help to obtain information about the relationship among implant design, distribution of bone stress, and bone growth. Finally, the adoption of a standardized approach will be necessary, in order to make FE modeling highly predictive of the implant’s long-term stability.

Straight antegrade intramedullary nails are generally inserted utilising the apex as the surgical entry point in accordance with the mechanical axis of the bone. Our objective is to optimise the bone-nail fit in intramedullary nailing by subjecting the surgical entry point to varying angulations in both the mediolateral and anterior-posterior directions via a quantitative fit assessment in each configuration to identify the optimal angulation, defined as the angulation with the lowest occurrence of thin-out to improve nail fitting within the humerus.

Computed tomography (CT) scans from 10 cadaveric humeri models were used to generate three-dimensional bone models. The centreline profile of each humerus model was determined by dividing the humerus into multiple slices and identifying its respective centroid. The guidewire and nail models were then established and inserted into the humerus using the apex as the standard entry point. The bone-nail fit was measured utilising three fit quantification parameters: thin-out distance, nail protrusion volume into the cortical shell and deviation distance (top, middle, bottom) between the nail's longitudinal axis and medullary cavity centroid.

Results revealed a statistically significant association between angulation and occurrence of thin-out (p < .001) and showed that the optimally angulated entry point resulted in decreased cortical breach across the nail insertion depth compared to the standard entry point.

Our findings suggested that the current straight nail design may require further modifications to optimise the nail trajectory within the medullary canal by decreasing the bone-nail geometric mismatch to potentially maximise its working length.