Validation of a novel finite-element model for evaluating patellofemoral forces and stress during squatting after posterior-stabilized total knee arthroplasty

INTRODUCTION

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.

HYPOTHESIS

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.

MATERIAL AND METHODS

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 130N 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.

RESULTS

Quadriceps force increased during flexion, up to 6 times the applied load. Von Mises stress on patellar implant increased up to 16MPa 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.

DISCUSSION

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.

CONCLUSION

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.

LEVEL OF EVIDENCE

IV, biomechanical computational study.

A Study of the Biomechanical Behavior of the Implantation Method of Inverted Shoulder Prosthesis (BIO⁻RSA) under Different Abduction Movements

The shoulder is the most mobile joint of the human body, but it is very fragile; several pathologies, and especially muscular degenerations in the elderly, can affect its stability. These are more commonly called rotator cuff fractures. In the case of this type of pathology, the mobility of the shoulder decreases and pain appears. In order to restore mobility and reduce pain, implantation of an inverted shoulder prosthesis is recommended. Unfortunately, over time a notch phenomenon has been observed. In the lower position of the arm, part of the implant comes into contact with the scapula and therefore causes deterioration of the bone. Among the solutions adopted is the lateralized method with bone grafting. However, a main disadvantage of this method concerns the reconstruction of the graft in the case of prosthesis revision. In this context, the aim of the present work was to reconstruct the shoulder joint in 3D in order to obtain a bio-faithful geometry, and then study the behavior of different types of biomaterials that can replace bone grafting. To this end, three arm abduction motions were examined for three individuals. From the results obtained, it appears that grafts in ultra-high molecular weight polyethylene (UHMWPE) exhibit a behavior closer to that of bones.

Influence of different dietary fats on the incorporation of exogenous fatty acids into rat adipose glycerides

Male Wistar rats were fed for 6 wk either a control low fat diet (1.5% sunflower seed oil) or a diet containing 10% fat: either saturated (coconut oil, cocoa butter) or unsaturated (olive oil, sunflower seed oil). In each dietary condition, in vitro incorporation of exogenously added fatty acids (ranging from capric to oleic acid) was studied in epididymal adipose glycerides. Analysis of variance of data revealed that there was a significant effect of the diet x substrate interaction. When results were expressed per cell lipid weight medium-chain fatty acids (capric and lauric) were esterified to a lesser extent than long-chain fatty acids regardless of the nature of dietary fat (saturated vs. unsaturated). The nature of dietary fat was found to have no effect on the incorporation of medium-chain fatty acids. Feeding saturated fats resulted in an increase of incorporation of long-chain fatty acids into adipose glycerides whereas feeding unsaturated fats did not modify fatty acid incorporation. Modifications of mean fat cell size by dietary fat could not account for all the observed variations.