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. 2025 Jan 7;12(1):41.
doi: 10.3390/bioengineering12010041.

Investigating the Reliability of Shore Hardness in the Design of Procedural Task Trainers

Kyleigh Kriener  1   2 , Kate Sinclair  1 , Grant Robison  1   2 , Raushan Lala  1 , Hayley Finley  1 , William Jase Richardson  1 , Mark J Midwinter  1
Affiliations

Investigating the Reliability of Shore Hardness in the Design of Procedural Task Trainers

Kyleigh Kriener et al. Bioengineering (Basel). .

Abstract

The haptic fidelity of biomimetic materials used in the design of procedural task trainers is of growing interest to the medical community. Shore hardness has been proposed as a method for assessing tissue biomechanics and replicating the results as a way to increase the fidelity of biomimetics to tissues. However, there is limited research on the reliability of human tissue measurements using Shore scales. Using human tissues (internal carotid artery [ICA], internal jugular vein [IJV], vagus nerve [VN], sternocleidomastoid muscle [SCM], and overlying skin [skin]), this study evaluates (1) the inter-rater reliability of Shore hardness measurements, (2) examines the relationship between tissue thickness and hardness, and (3) investigates the impact of a measurement method (freehand vs. durometer stand). Preserved tissues, specifically a liver and components of the anterior triangle of the neck, were extracted from cadavers and measured by three independent raters using digital Shore durometers. Testing revealed that although Shore A demonstrated better inter-rater reliability compared to Shore OO, both scales exhibited poor-to-moderate reliability. ICC values for Shore A ranged from 0.21 to 0.80 and were statistically significant (p < 0.05) for all tissue types except the SCM. In contrast, Shore OO demonstrated poorer reliability, with ICC values ranging from 0.00 to 0.41. The ICC values were only significant for the ICA, IJV, and VN (p < 0.05). An inverse correlation between tissue thickness and hardness on the Shore A scale was found for all tissues and was significant (p < 0.05) for ICA, VN, and skin. There were mixed results for the correlation between tissue thickness and hardness on the Shore OO scale (-0.06-0.92), and only IJV had a statistically significant correlation (p < 0.05). Finally, the median hardness values on the Shore OO scale were significantly greater when measured using a durometer stand vs. freehand (Z = 4.78, p < 0.05). In summary, when using appropriate standards and addressing the challenges of tissue thickness and variability in freehand measures, Shore hardness has the potential to be used by clinicians in the clinical setting and in the selection of biomimetic materials in the design of task trainers.

Keywords: Shore hardness; biomechanics; human tissues; physician training; procedural task trainer; reliability; simulation design.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Longitudinal opening of the ICA and IJV for hardness testing.
Figure 2
Figure 2
Digital durometer and stage with weight used to collect Shore hardness specimens.
Figure 3
Figure 3
Plot of the expected confidence interval width vs. number of samples. Calculations were based on the absolute agreement coefficient (p^) for each tissue type.
Figure 4
Figure 4
ICC values, CI, and significance for the measured hardness of different human tissues using the Shore A and OO scales. The asterisks (*) indicate significant ICC values (p < 0.05).
Figure 5
Figure 5
Correlation coefficients for the association between tissue thickness (mm) and Shore scale are represented by the filled circles. The bars around the circles are the 95% CI of the correlation coefficients.
Figure 6
Figure 6
Rater taking freehand Shore OO measure from the surface of a liver.
Figure 7
Figure 7
Notched boxplot showing the data distribution for Shore OO measurements on the surface of a liver.
See this image and copyright information in PMC

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