Validation of the suction device Nimble for the assessment of skin fibrosis in systemic sclerosis

Intra- and inter-rater reliabilities of skin mechanical properties measured in healthy individuals using skin elasticity meter

PURPOSE

The aim of this study is to establish a standardized measurement method and to examine the intra- and inter-reliabilities and absolute reliability of measuring skin mechanical properties using a skin elasticity meter (Cutometer®).

METHODS

Ten healthy participated in the study. Skin mechanical properties were measured at four sites: upper arm, lower arm, upper leg and lower leg on both sides in supine position using a non-invasive skin elasticity meter by two trained different raters. The measurements include quantitative indices of the maximal distensibility (R0), elasticity (R2, R5, R7), and viscoelasticity (R6). Intra- and inter- relative reliabilities were determined using the intraclass correlation coefficient (ICC) (1,1) and ICC (2,1) methods, respectively. The absolute reliability was assessed via the Bland-Altman analysis. Moreover, we evaluated the minimal detectable change at a 95% confidence level (MDC95).

RESULTS

At each site, the ICC (1,1) values were >0.90, and the ICC (2,1) values were >0.50. The Bland-Altman analysis did not reveal any fixed errors, and several sites and parameters have proportional errors.

CONCLUSIONS

In this study, intra- and inter-reliabilities were measured at "excellent" and more than "moderate" levels, respectively. However, because some proportional errors were observed, the limits of reliability agreement should be considered when using the proposed methods. We believe that the results of this study can be applied to clinical research in field of rehabilitation treatment.

Water flow elastography - A promising tool to measure tissue stiffness during minimally invasive surgery

Mechanical properties are important markers for pathological processes in tissue. Elastography techniques are therefore becoming more and more useful for diagnostics. In minimally invasive surgery (MIS), however, the probe size is limited and the handling is restricted, thereby excluding the application of most established elastography techniques. In this paper we introduce water flow elastography (WaFE) as a new technique that benefits from a small and inexpensive probe. This probe flows pressurized water against the sample surface to locally indent it. The volume of the indentation is measured with a flow meter. We use finite element simulations to find the relation between the indentation volume, the water pressure, and the Young's modulus of the sample. We used WaFE to measure the Young's modulus of silicone samples and porcine organs, finding agreement within 10% to measurements with a commercial material testing machine. Our results show that WaFE is a promising technique for providing local elastography in MIS.

A quantitative comparison of devices for in vivo biomechanical characterization of human skin

Non-invasive skin characterization devices are emerging as a valuable tool in clinical skin research. In recent years, the range of available experimental techniques and methods used to determine the biomechanical properties of skin has increased considerably. Although a substantial amount of work has been devoted to assessing the working principle of macroscopic skin characterization devices individually, a rationalization and comparison between them is still lacking. This motivated the present study, which aimed to characterize and compare three commonly used working principles: suction, dynamic shear loading, and indentation. A synthetic model system with tunable mechanical properties was used to assess the three devices, and the results rationalized based on corresponding finite element models. In vivo measurements were performed on healthy volunteers to investigate the capability of differentiating the biomechanical properties of skin at different body locations, and to assess the intra- and inter-rater reliability of each device. The present comparative analysis indicates that the analyzed functional principles perceive the stiffness of human skin differently, with relevant implications for the interpretation of the respective measurement results.

Standardizing Dimensionless Cutometer Parameters to Determine In Vivo Elasticity of Human Skin

Objective: Skin fibrosis places an enormous burden on patients and society, but disagreement exists over methods to quantify severity of skin scarring. A suction cutometer measures skin elasticity in vivo, but it has not been widely adopted because of inconsistency in data produced. We investigated variability of several dimensionless parameters generated by the cutometer to improve their precision and accuracy. Approach: Twenty adult human subjects underwent suction cutometer measurement of normal skin (NS) and fibrotic scars (FS). Using Mode 1, each subject underwent five trials with each trial containing four curves. R0/2/5/6/7 and Q1/2/3 data were collected. Analyses were performed on these calculated parameters. Results: R0/2/5/6/7 and Q1/2 parameters from curves 1 to 4 demonstrated significant differences, whereas these same parameters were not significantly different when only using curves 2-4. Individual analysis of all parameters between curve 1 and every subsequent curve was statistically significant for R0, R2, R5, R6, R7, Q1, and Q2. No differences were appreciated for parameter Q3. Comparison between NS and FS were significantly different for parameters R5, Q1, and Q3. Innovation: Our study is the first demonstration of accurate comparison between NS and FS using the dimensionless parameters of a suction cutometer. Conclusions: Measured parameters from the first curve of each trial were significantly different from subsequent curves for both NS and FS. Precision and reproducibility of data from dimensionless parameters can therefore be improved by removing the first curve. R5, Q1, and Q3 parameters differentiated NS as more elastic than FS.

Longitudinal monitoring and prediction of long-term outcome of scar stiffness on pediatric patients

Background

Hypertrophic scarring after burn injury is one of the greatest unmet challenges in patients with burn injuries. A better understanding of the characteristics of scar maturation and early prediction of the long-term outcome of scarring are prerequisites for improving targeted therapies and pivotal for patient counselling.

Methods

Repeated measurements of scar stiffness in 11 pediatric patients were performed over the course of 1 year using 2 suction devices, the Cutometer and the Nimble. In addition, the observer pliability score of the Patient and Observer Scar Assessment Scale was applied. This longitudinal study allowed quantification of the ability of each of the measured parameters to reflect scar maturation, as indicated by change in skin pliability/stiffness, over time (using linear regression); the ability to distinguish individual patients (intraclass correlation coefficient (ICC)); the correlation of the devices (Spearman correlation coefficient); and the ability to predict long-term scar maturation based on early scar assessment (using receiver operating characteristic).

Results

All the tools used showed significant longitudinal decrease of scar stiffness from 3 months until 12 months after the injury. The Nimble (ICC_patient ^Nimble = 0.99) and the Cutometer (ICC_patient ^Cuto = 0.97) demonstrated an excellent ability to distinguish between individual patients. The Nimble seemed to be able to predict the 12-month pliability of scars based on early (3-month) measurements (area under the curve (AUC)_12m ^POSAS = 0.67; AUC_12m ^C = 0.46; AUC_12m ^N = 0.79).

Conclusions

The results of this preliminary study suggest that all 3 tools provide suitable means to quantify alterations in scar stiffness over time. Initial evidence suggests the Nimble is most favorable for predicting changes in stiffness associated with long-term scar maturation. Further studies with a larger sample size are required to validate tissue suction as a clinical tool for analysis of changes of scar stiffness over time.