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Plantar soft tissue stiffness plays a crucial role in the development of diabetic foot complications, but in vivo assessments are constrained by anatomical variability and probe-induced measurement artifacts. To develop anatomically layered polyurethane phantom models mimicking healthy and diabetic plantar soft tissues and evaluate the reliability and concurrent validity of four mechanical stiffness assessment tools, [MyotonPRO, Shore Durometer, IndentoPRO, and Tissue Compliance Meter (TCM)] against Shear Wave Elastography (SWE).

Six regional phantom models (calcaneus, midfoot, forefoot) with skin, fat pad, fascia, and muscle layers were fabricated. SWE was performed in no-contact mode to eliminate surface compression, improving measurement consistency. A total of 162 configurations were tested under blinded and randomized conditions. Intra- and inter-rater reliability was assessed using ICCs; concurrent validity was evaluated via correlation and regression analyses with SWE.

All devices demonstrated excellent reliability (ICC range: 0.88–0.99). SWE-derived stiffness was significantly higher in diabetic models, especially in the calcaneal and midfoot regions (p < 0.001). IndentoPRO showed the highest correlation with SWE (r = 0.91), followed by MyotonPRO (r = 0.87), TCM (r = 0.85), and Durometer (r = 0.78). TCM exhibited the highest predictive value (R2 = 0.502) and most consistent performance across diabetic regions.

The developed phantom models offer a standardized platform for evaluating stiffness assessment tools. While SWE remains the reference standard, mechanical devices, particularly TCM and IndentoPRO, demonstrated valid and reproducible performance. This phantom-based approach holds promise for supporting medical device development, regulatory validation, and preclinical testing in diabetic foot biomechanics.

Keywords: diabetic foot, plantar soft tissue, stiffness measurement, phantom model, foot biomechanics

This study demonstrated that four mechanical devices (MyotonPRO, Shore Durometer, IndentoPRO and TCM) are reliable and valid tools for assessing plantar soft tissue stiffness using multilayer polyurethane phantom models simulating healthy and diabetic foot conditions. All devices showed excellent intra- and inter-rater reliability and significant correlations with SWE-derived reference values, supporting their concurrent validity. Each device exhibited distinct strengths depending on tissue depth: the TCM and IndentoPRO were particularly effective in assessing deeper tissue stiffness, while the MyotonPRO and Shore Durometer were better suited for evaluating more superficial layers. Although phantom models cannot fully simulate the complexity of biological tissues, they offer a reproducible and standardized platform for evaluating device performance across anatomically relevant regions. This phantom-based approach may also support early-phase medical device evaluation, particularly in situations where in vivo testing is not immediately feasible. Moving forward, enhancing anatomical realism, validating findings in clinical settings, and integrating these tools with complementary diagnostics will be essential for advancing their clinical utility in diabetic foot care.