Evaluation of breast skin and tissue stiffness using a non-invasive aspiration device and impact of clinical predictors.

A personalized 3D breast model could present a real benefit for preoperative discussion with patients, surgical planning, and guidance. Breast tissue biomechanical properties have been poorly studied in vivo, although they are important for breast deformation simulation. The main objective of our study was to determine breast skin thickness and breast skin and adipose/fibroglandular tissue stiffness. The secondary objective was to assess clinical predictors of elasticity and thickness: age, smoking status, body mass index, contraception, pregnancies, breastfeeding, menopausal status, history of radiotherapy or breast surgery. Participants were included at the Montpellier University Breast Surgery Department from March to May 2022. Breast skin thickness was measured by ultrasonography, breast skin and adipose/fibroglandular tissue stiffnesses were determined with a VLASTIC non-invasive aspiration device at three different sites (breast segments I-III). Multivariable linear models were used to assess clinical predictors of elasticity and thickness. In this cohort of 196 women, the mean breast skin and adipose/fibroglandular tissue stiffness values were 39 and 3 kPa, respectively. The mean breast skin thickness was 1.83 mm. Only menopausal status was significantly correlated with breast skin thickness and adipose/fibroglandular tissue stiffness. The next step will be to implement these stiffness and thickness values in a biomechanical breast model and to evaluate its capacity to predict breast tissue deformations.

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.

In vivo quantification of 3D displacement in sacral soft tissues under compression: Relevance of 2D US-based measurements for pressure ulcer risk assessment.

OBJECTIVE: 2D Ultrasound (US) imaging has been recently investigated as a more accessible alternative to 3D Magnetic Resonance Imaging (MRI) for the estimation of soft issue motion under external mechanical loading. In the context of pressure ulcer prevention, the aim of this pilot MRI study was to design an experiment to characterize the sacral soft tissue motion under a controlled mechanical loading. Such an experiment targeted the estimation of the discrepancy between tissue motion assessed using a 2D imaging modality (echography) versus tissue motion assessed using a (reference) 3D imaging modality (MRI). METHODS: One healthy male volunteer participated in the study. An MRI-compatible custom-made setup was designed and used to load the top region of the sacrum with a 3D-printed copy of the US transducer. Five MR images were collected, one in the unloaded and four in the different loaded configurations (400-1200 [g]). Then, a 3D displacement field for each loading configuration was extracted based on the results of digital volume correlation. Tissue motion was separated into the X, Y, Z directions of the MRI coordinate system and the ratios between the out-of-plane and in-plane components were assessed for each voxel of the selected region of interest. RESULTS: Ratios between the out-of-plane and in-plane displacement components were higher than 0.6 for more than half of the voxels in the region of interest for all load cases and higher than 1 for at least quarter of the voxels when loads of 400-800 [g] were used. CONCLUSION: The out-of-ultrasound-plane tissue displacement was not negligible, therefore 2D US imaging should be used with caution for the evaluation of the tissue motion in the sacrum region. The 3D US modality should be further investigated for this application.

MR-based quantitative measurement of human soft tissue internal strains for pressure ulcer prevention.

Pressure ulcers are a severe disease affecting patients that are bedridden or in a wheelchair bound for long periods of time. These wounds can develop in the deep layers of the skin of specific parts of the body, mostly on heels or sacrum, making them hard to detect in their early stages. Strain levels have been identified as a direct danger indicator for triggering pressure ulcers. Prevention could be possible with the implementation of subject-specific Finite Element (FE) models. However, generation and validation of such FE models is a complex task, and the current implemented techniques offer only a partial solution of the entire problem considering only external displacements and pressures, or cadaveric samples. In this paper, we propose an in vivo solution based on the 3D non-rigid registration between two Magnetic Resonance (MR) images, one in an unloaded configuration and the other deformed by means of a plate or an indenter. From the results of the image registration, the displacement field and subsequent strain maps for the soft tissues were computed. An extensive study, considering different cases (on heel pad and sacrum regions) was performed to evaluate the reproducibility and accuracy of the results obtained with this methodology. The implemented technique can give insight for several applications. It adds a useful tool for better understanding the propagation of deformations in the heel soft tissues that could generate pressure ulcers. This methodology can be used to obtain data on the material properties of the soft tissues to define constitutive laws for FE simulations and finally it offers a promising technique for validating FE models.

New pressure ulcers dressings to alleviate human soft tissues: A finite element study.

Pressure Ulcers (PU) are real burdens for patients in healthcare systems, affecting their quality of life. External devices such as prophylactic dressings may be used to prevent the onset of PU. A new type of dressing was designed to alleviate soft tissue under pressure, with the objective to prevent PU and to improve the healing conditions of category-1 and category-2 wounds. The mechanical interactions of this dressing with a generic model of human skin/hypodermal soft tissue was simulated using the Finite Element (FE) method. Different cases with intact skin tissues and injured tissues with a category-2 PU, with and without dressings in place, were modeled. The tissues were deformed under compressive load; internal strains were computed. The results showed a clear benefit from the use of the dressing to reduce the peak internal strains both in the intact and injured tissues models by 17-25%, respectively. The intact soft tissues model was evaluated via sacral pressure measurements performed on one healthy volunteer. Results showed a good agreement between pressure measurements and estimations both with and without the dressing in place; particularly under the bony prominence and in surrounding tissues. As a conclusion, the importance of dressings to maintain a proper biochemical environment for the healing of PU is incontestable. Yet, new concepts of dressings may be developed to prevent the onset of PU, but also to provide local stress and strain reliefs and create mechanical conditions as less damaging as possible for the tissues.

Development and Operation of an Experimental System to Measure the Moments Generated in the Finger Joints.

Little information is available on the forces that fingers can generate, and few devices exist to measure the forces they can create. The objective of this paper is to propose an experimental device to measure the moments generated by finger joints. The idea is to focus on a single joint and not on the effort generated by the whole finger. A system leaving only one joint free is developed to measure the maximum attainable moment in different joint positions between the extended and flexed finger. The device is tested on the proximal interphalangeal joints of the index fingers of thirty people for both hands. The results show a dispersion of results from one person to another but with similar trends in the evolution of the maximum achievable moment depending on the angle. Average values of the maximum moments attained by men and women for both hands are given for all angular positions of the joint. The results are analysed using principal component analysis. This analysis shows that four main modes represent more than 99% of the signal and allow the reconstruction of all the data for all the subjects. The four modes obtained can be used as a basis for the development of finger devices by hospital practitioners.

Reliability of B-mode ultrasound and shear wave elastography in evaluating sacral bone and soft tissue characteristics in young adults with clinical feasibility in elderly.

BACKGROUND: Physiologic aging is associated with loss of mobility, sarcopenia, skin atrophy and loss of elasticity. These factors contribute, in the elderly, to the occurrence of a pressure ulcer (PU). Brightness mode ultrasound (US) and shear wave elastography (SWE) have been proposed as a patient-specific, bedside, and predictive tool for PU. However, reliability and clinical feasibility in application to the sacral region have not been clearly established. METHOD: The current study aimed to propose a simple bedside protocol combining US and SWE. The protocol was first tested on a group of 19 healthy young subjects by two operators. The measurements were repeated three times. Eight parameters were evaluated at the medial sacral crest. Intraclass Correlation Coefficient (ICC) was used for reliability assessment and the modified Bland Altman plot analysis for agreement assessment. The protocol was then evaluated for clinical feasibility on a healthy older group of 11 subjects with a mean age of 65 ± 2.4 yrs. FINDINGS: ICC showed poor to good reliability except for skin SWE and hypodermis thickness with an ICC (reported as: mean (95%CI)) of 0.78 (0.50-0.91) and 0.98 (0.95-0.99) respectively. No significant differences were observed between the young and older group except for the muscle Shear Wave Speed (SWS) (respectively 2.11 ± 0.27 m/s vs 1.70 ± 0.17 m/s). INTERPRETATION: This is the first protocol combining US and SWE that can be proposed on a large scale in nursing homes. Reliability, however, was unsatisfactory for most parameters despite efforts to standardize the protocol and measurement definitions. Further studies are needed to improve reliability.