MR-compatible loading device for assessment of heel pad internal tissue displacements under shearing load

Finite Element Tissue Strains Computation to Evaluate the Mechanical Protection Provided by a New Bilayer Dressing for Heel Pressure Injuries

OBJECTIVE

Pressure injuries (PIs) result in an extended duration of care and increased risks of complications for patients. When treating a PI, the aim is to hinder further PI development and speed up the healing time. Urgo RID recently developed a new bilayer dressing to improve the healing of stages 2 and 3 heel PIs. This study aims to numerically investigate the efficiency of this new bilayer dressing to reduce strains around the PI site.

METHODS

The researchers designed three finite element models based on the same heel data set to compare the Green-Lagrange compressive and maximal shear strains in models without a PI, with a stage 2 PI, and with a stage 3 PI. Simulations with and without the dressing were computed. Analysis of the results was performed in terms of strain clusters, defined as volumes of tissues with high shear and compressive strains.

RESULTS

Decreases in the peak and mean values of strains were low in all three models, between 0% and 20%. However, reduction of the strain cluster volumes was high and ranged from 55% to 68%.

CONCLUSIONS

The cluster analysis enables the robust quantitative comparison of finite element analysis. Results suggest that use of the new bilayer dressing may reduce strain around the PI site and that this dressing could also be used in a prophylactic manner. Results should be extended to a larger cohort of participants.

Definition and evaluation of a finite element model of the human heel for diabetic foot ulcer prevention under shearing loads

Diabetic foot ulcers are triggered by mechanical loadings applied to the surface of the plantar skin. Strain is considered to play a crucial role in relation to ulcer etiology and can be assessed by Finite Element (FE) modeling. A difficulty in the generation of these models is the choice of the soft tissue material properties. In the literature, many studies attempt to model the behavior of the heel soft tissues by implementing constitutive laws that can differ significantly in terms of mechanical response. Moreover, current FE models lack of proper evaluation techniques that could estimate their ability to simulate realistic strains. In this article, we propose and evaluate a FE model of the human heel for diabetic foot ulcer prevention. Soft tissue constitutive laws are defined through the fitting of experimental stretch-stress curves published in the literature. The model is then evaluated through Digital Volume Correlation (DVC) based on non-rigid 3D Magnetic Resonance Image Registration. The results from FE analysis and DVC show similar strain locations in the fat pad and strain intensities according to the type of applied loads. For additional comparisons, different sets of constitutive models published in the literature are applied into the proposed FE mesh and simulated with the same boundary conditions. In this case, the results in terms of strains show great diversity in locations and intensities, suggesting that more research should be developed to gain insight into the mechanical properties of these tissues.