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

Mechanical properties of extrinsic foot muscles, Achilles tendon, and plantar fascia in patients with a history of diabetic foot ulcers

BACKGROUND

Diabetic foot ulcers (DFU) are a major complication of diabetes, often leading to impaired mobility and increased risk of recurrence due to persistent biomechanical alterations. Understanding the mechanical properties of foot muscles, tendons, and fascia may provide insight into ulcer development, prevention and rehabilitation strategies. This study aimed to assess the biomechanical properties of the extrinsic foot muscles, Achilles tendon (AT), and plantar fascia (PF) in individuals with a history of DFU using myotonometry.

METHODS

A total of 38 diabetic feet with a history of DFU (Wagner Grade 0-1) and 40 healthy controls (HC) were evaluated. The MyotonPRO device was used to measure muscle tone (Natural Oscillation Frequency, F), stiffness, and elasticity in the tibialis anterior (TA), gastrocnemius medialis (GM), gastrocnemius lateralis (GL), AT, and PF. Measurements were performed in standardized positions, with statistical comparisons made between groups using independent t-tests.

RESULTS

TA and GM showed significantly increased muscle tone and stiffness in the DFU group compared to HC (p < 0.05), whereas GL did not exhibit significant differences. Similarly, PF and AT stiffness were higher in the DFU group (p < 0.05), suggesting alterations in tissue load distribution. No significant differences in elasticity were observed between groups.

CONCLUSIONS

This study highlights persistent mechanical alterations in the TA, GM, AT, and PF in individuals with a history of DFU, despite ulcer healing. The increased stiffness and tone in these structures may contribute to abnormal foot loading patterns, potentially increasing the risk of ulcer recurrence. The findings emphasize the importance of early biomechanical assessment and targeted rehabilitation strategies, such as neuromuscular training, load redistribution, Achilles tendon stretching and custom orthotic interventions to mitigate mechanical dysfunction in diabetic foot patients.

CLINICAL TRIAL NUMBER

Not applicable.

Numerical evaluations of different foot arch types: effects of loading on plantar pressure distribution and bone stress

This study aimed to investigate the biomechanical variations among different types of foot arches. Plantar pressure and foot bone stress of three arch types under bipedal standing, single foot standing and running mid-stance were investigated by simulation. Compared with the normal foot, the stress in the hind foot area of high arch foot increased significantly, while the contact area of the low arch foot increased. Bone stress in high arch increased more significantly when changed from bipedal standing to single foot standing or running. The results support the link between abnormal arches and foot pain, providing design basis for orthopedic insoles.

Volumetric Ultrasound of the Plantar Soft Tissue Under Bodyweight Loading

OBJECTIVE

This work aims to develop a device capable of acquiring volumetric scans of the plantar soft tissue in naturally loaded and unloaded states using ultrasound B-mode imaging and shear wave elastography.

METHODS

Materials were investigated for acoustic transmission and bodyweight loading. A mechanical scanning apparatus was constructed using a compatible load bearing material and two perpendicular linear actuators. Custom software was developed to control the scanner, record subject and scan information, and reconstruct acquired ultrasound images and shear wave speed values into a volume. The system was evaluated using custom-developed ultrasound phantoms.

RESULTS

Plastic materials reduced axial and lateral resolution by 0.25 - 0.5 mm and reduced SWE values by 0.8 to 26 kPa. The developed system produced volumetric scans within 0.1 to 1.6 mm of expected dimensions on a geometric phantom compared to 0 to 0.6 mm in standard computed tomography. Acoustic thermal increases were 0 °C for B-mode and .9 to 2.9 °C for SWE. Volumes of an anatomically realistic phantom and a pilot scan yielded clear anatomic features.

CONCLUSION

The resulting system is capable of producing volumetric plantar soft tissue scans in both B-mode and shear wave elastography with resolution on par with existing volumetric medical imaging systems.

SIGNIFICANCE

This system images plantar soft tissue volumes under physiologic loads.

An overview of current developments and methods for identifying diabetic foot ulcers: A survey

Diabetic foot ulcers (DFUs) present a substantial health risk across diverse age groups, creating challenges for healthcare professionals in the accurate classification and grading. DFU plays a crucial role in automated health monitoring and diagnosis systems, where the integration of medical imaging, computer vision, statistical analysis, and gait information is essential for comprehensive understanding and effective management. Diagnosing DFU is imperative, as it plays a major role in the processes of diagnosis, treatment planning, and neuropathy research within automated health monitoring and diagnosis systems. To address this, various machine learning and deep learning‐based methodologies have emerged in the literature to support healthcare practitioners in achieving improved diagnostic analyses for DFU. This survey paper investigates various diagnostic methodologies for DFU, spanning traditional statistical approaches to cutting‐edge deep learning techniques. It systematically reviews key stages involved in diabetic foot ulcer classification (DFUC) methods, including preprocessing, feature extraction, and classification, explaining their benefits and drawbacks. The investigation extends to exploring state‐of‐the‐art convolutional neural network models tailored for DFUC, involving extensive experiments with data augmentation and transfer learning methods. The overview also outlines datasets commonly employed for evaluating DFUC methodologies. Recognizing that neuropathy and reduced blood flow in the lower limbs might be caused by atherosclerotic blood vessels, this paper provides recommendations to researchers and practitioners involved in routine medical therapy to prevent substantial complications. Apart from reviewing prior literature, this survey aims to influence the future of DFU diagnostics by outlining prospective research directions, particularly in the domains of personalized and intelligent healthcare. Finally, this overview is to contribute to the continual evolution of DFU diagnosis in order to provide more effective and customized medical care.

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Current poisson's ratio values of finite element models are too low to consider soft tissues nearly-incompressible: illustration on the human heel region

Tissues' nearly incompressibility was well reported in the literature but little effort has been made to compare volume variations computed by simulations with in vivo measurements. In this study, volume changes of the fat pad during controlled indentations of the human heel region were estimated from segmented medical images using digital volume correlation. The experiment was reproduced using finite element modelling with several values of Poisson's ratio for the fat pad, from 0.4500 to 0.4999. A single value of Poisson's ratio could not fit all the indentation cases. Estimated volume changes were between 0.9% - 11.7%.

Subject-specific material properties of the heel pad: An inverse finite element analysis

Individuals with diabetes are at a higher risk of developing foot ulcers. To better understand internal soft tissue loading and potential treatment options, subject-specific finite element (FE) foot models have been used. However, existing models typically lack subject-specific soft tissue material properties and only utilize subject-specific anatomy. Therefore, this study determined subject-specific hindfoot soft tissue material properties from one non-diabetic and one diabetic subject using inverse FE analysis. Each subject underwent cyclic MRI experiments to simulate physiological gait and to obtain compressive force and three-dimensional soft tissue imaging data at 16 phases along the loading-unloading cycles. The FE models consisted of rigid bones and nearly-incompressible first-order Ogden hyperelastic skin, fat, and muscle (resulting in six independent material parameters). Then, calcaneus and loading platen kinematics were computed from imaging data and prescribed to the FE model. Two analyses were performed for each subject. First, the skin, fat, and muscle layers were lumped into a single generic soft tissue material and optimized to the platen force. Second, the skin, fat, and muscle material properties were individually determined by simultaneously optimizing for platen force, muscle vertical displacement, and skin mediolateral bulging. Our results indicated that compared to the individual without diabetes, the individual with diabetes had stiffer generic soft tissue behavior at high strain and that the only substantially stiffer multi-material layer was fat tissue. Thus, we suggest that this protocol serves as a guideline for exploring differences in non-diabetic and diabetic soft tissue material properties in a larger population.

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.