Validation of a laser‐assisted wound measurement device in a wound healing model

Abstract

In the treatment and monitoring of a diabetic or chronic wound, accurate and repeatable measurement of the wound provides indispensable data for the patient's medical record. This study aims to measure the accuracy of the laser‐assisted wound measurement (LAWM) device against traditional methods in the measurement of area, depth and volume. We measured four ‘healing’ wounds in a Play‐Doh^®‐based model over five subsequent states of wound healing progression in which the model was irregularly filled in to replicate the healing process. We evaluated the LAWM device against traditional methods including digital photograph assessment with National Institutes of Health ImageJ software, measurements of depth with a ruler and weight‐to‐volume assessment with dental paste. Statistical analyses included analysis of variance (ANOVA) and paired t‐tests. We demonstrate that there are significantly different and nearly statistically significant differences between traditional ruler depth measurement and LAWM device measurement, but there are no statistically significant differences in area measurement. Volume measurements were found to be significantly different in two of the wounds. Rate of percentage change was analysed for volume and depth in the wound healing model, and the LAWM device was not significantly different than the traditional measurement technique. While occasionally inaccurate in its absolute measurement, the LAWM device is a useful tool in the clinician's arsenal as it reliably measures rate of percentage change in depth and volume and offers a potentially aseptic alternative to traditional measurement techniques.

Introduction

Diabetes mellitus presents a growing challenge for both providers and patients at both the national and global scale 1. Early detection and treatment of diabetes can ameliorate some of the dire consequences of the disease; however, studies indicate that over 50% of patients with diabetes are not aware that they indeed have the disease 2. Uncontrolled diabetes, either through patients' inability to follow treatment guidelines or through simply being unaware of their disease, can manifest itself in the form of a diabetic foot wound or ulcer 3. These diabetic foot wounds manifest themselves in 15–25% of patients with diabetes, and have an even greater chance of reoccurrence, as high as 50–70%, over the next 5 years 4, 5, 6. These diabetic foot wounds are responsible for 85% of all non‐traumatic lower extremity amputations in the USA, and the risk of lower extremity amputation is 15–46 times greater in the population with diabetes than the population without diabetes 7, 8, 9, 10, 11. Even in specialised diabetic foot wound care centres, treatment and healing is a slow process, averaging over 2 months, and must be tracked carefully to provide optimal treatment 12.

As the disease burden of diabetes, especially diabetic foot wounds, continues to grow and treatment standards require careful tracking of wound progress, clinicians will increasingly need to rely on technological improvements in wound measurement technologies to track the progress of their treatments and attempt to avoid these often debilitating lower extremity amputations.

In the treatment and monitoring of a chronic wound, accurate and repeatable measurement of the wound provides indispensable data for the patient's medical record. These data help determine treatment course, determine the progress of the wound and present a relevant clinical data point through which health care practitioners are able to communicate.

Laser‐assisted wound measurement (LAWM) devices represent the next step in which medicine and wound care become intertwined with technology. The LAWM device studied aims to meet the goal of any medical technology in that it is safe, accurate and cost‐effective; however, these three goals must equal or exceed the status quo if the device is to be considered an effective tool in the clinician's toolbox – three goals that have been inconsistently fulfilled by other advanced wound measurement devices 13, 14, 15, 16. This study aims to measure the accuracy of the LAWM device against traditional methods as well as highly accurate methods that currently cannot be replicated clinically 17.

In a previously published study by our group, we assessed the accuracy of a LAWM device to measure cylindrical wounds (both artificial and porcine) that were to be easily and accurately measured by hand. Although these measures were relatively accurate, depth measurements were inaccurate by a consistent amount. This study attempts to further our understanding of the LAWM devices' accuracy by creating more realistic wounds with a ‘healing’ wound model. Area and depth of wounds were measured with the LAWM device and standard hand measurement methods currently in use such as digital photography, rulers and wound tracing with the National Institutes of Health (NIH) ImageJ software 18, 19. Volume measurements compared the LAWM device's proprietary volume calculation with a weight‐to‐volume measurement using dental paste.

Methods

Wound model creation

Four irregular wound models were created using Play‐Doh^® and were labelled as A, B, C and D. These four wound models were irregularly filled in to represent five subsequent states of progressive wound healing, including a ‘hypergranulation’ state.

Measurement of wound area

Each wound model was photographed from a fixed height and angle with a digital camera with a ruler. The wound area from each photograph was measured three times using NIH ImageJ software, using the ruler as a scale for the software analysis. Wound areas obtained from the LAWM device (Silhouette Star™, Aranz, Christchurch, NZ) were measured three times as per the manufacturer's instructions and were averaged.

Measurement of wound depth

The depth of each wound was measured using a ruler at six fixed locations (10, 12, 2, 4, 6 and 8 o'clock) along the wound margin. Ruler depth measurements were placed in three groups of two and averaged together to give a mean ruler depth measurement. Mean wound depths from the LAWM device were measured three times as per the manufacturer's instructions and were averaged. Maximum depth measurements from the LAWM device were also collected three times and were averaged.

Measurement of wound volume

Each of the wounds and their subsequent ‘healing state’ were filled with Jeltrate^® (Pearson Dental Supply Co, Sylmar, CA) fast‐set dental paste, which was mixed using 5·43 ml/g of Jeltrate powder. The paste mould was allowed to set for 5 minutes, and then was removed and weighed. Volume was calculated from these weights using a standard curve equation, which was determined from obtaining the weights of known volumes. Wound volume was also calculated nine times using each of the three ImageJ area measurements along with each of the three average ruler depth measurements. These wound volume measurements were compared with the wound volume obtained from the LAWM device as per the manufacturer's instructions. Volume was also calculated from using the LAWM device area measurement and the LAWM device maximum depth measurement for further comparison.

Data analysis and statistics

The repeated measurements obtained by ImageJ, Jeltrate and LAWM were averaged, and standard deviation was calculated for each wound and wound state. Student's paired t‐test and analysis of variance (ANOVA), when applicable, were used to determine whether wound measurements (area, depth, volume and error) were different for each measurement. Post hoc multiple comparison analysis was used in conjunction with the ANOVA test. P > 0·05 was considered the threshold for statistical significance. All data were analysed using Microsoft Excel 2008 for Mac (Redmond, WA) and GraphPad Prism 6 (La Jolla, CA) statistical software.

Results

Data are presented as the average measurement and standard deviation for each wound. To analyse the LAWM device's ability to measure the depth, each of the four wounds was measured three times for each healing state, which was then compared with ruler measurements at six different positions on the four ‘healing’ wounds (Figure 1). Statistically significant differences between the LAWM device and ruler measurement were noted in Wound B (P = 0·029), whereas differences between the LAWM device and standard measurement approached statistical significance in Wound A (P = 0·059), Wound C (P = 0·069) and Wound D (P = 0·054).

Figure 1.

Ruler depth measurement compared with LAWM depth measurement from the Aranz Silhouette Star.

Paired t‐tests analysing the area calculated from ImageJ tracings compared with the LAWM device digital photograph with tracing showed no statistically significant difference between the two methods of measurement (Figure 2); however, the area measurements for Wounds B and D approached statistical significance (P = 0·080 and P = 0·079, respectively).

Figure 2.

Wound area measurements using NIH ImageJ with digital photography and the Aranz Silhouette Star.

LAWM device volume measurements were compared with ruler depth measurements multiplied by ImageJ area measurement as well as Jeltrate dental paste measurement, which used the paste's ability to form a mould of the wound volume that was then calculated to yield a weight‐to‐volume ratio (Figure 3). ANOVA study of the three methods for measuring volume, Jeltrate, the LAWM device and mean ruler depth × ImageJ area demonstrated a significant difference in Wound C (P = 0·032) and Wound D (P = 0·027). Post hoc multiple comparisons analysis of the ANOVA results showed a significant difference between the Jeltrate measurement and the LAWM measurement for both Wounds C and D.

Figure 3.

Wound volume measurement using Jeltrate dental paste, hand measurement (ImageJ × ruler) and Aranz Silhouette Star.

Rate of percentage change in depth and volume was similarly analysed (Figures 4 and 5). There was no significant difference between the LAWM device and the ruler measurement when considering the differences in the rates of change captured by the two devices. Volumetric rate of change was significantly different as measured by ANOVA for Wounds C and D; however, post hoc analysis demonstrated significant differences between the rates of volume change measurements when comparing hand ImageJ × ruler calculations with the Jeltrate measurement.

Figure 4.

Rate of percentage change in wound depth during healing progression comparing the Aranz Silhouette Star with traditional ruler measurement.

Figure 5.

Rate of percentage change in wound volume during healing progression comparing Jeltrate (dental paste), hand (ImageJ × ruler) and Aranz Silhouette Star.

Discussion

Laser‐assisted wound measurement devices ostensibly offer a less invasive method for physicians, nurses and other health care practitioners to assess wound healing; however, these new systems must either exceed or be comparable to the status quo.

Several studies have indicated that LAWM devices and specifically the Aranz Medical Silhouette provides accurate measurement, low inter‐ and intrarater variability and a relatively easy‐to‐use system 20, 21, 22, 23. In a highly controlled setting, our first study on LAWM devices indicated that accuracy in determining area was consistent with digital photography combined with tracing on ImageJ software, but consistently and predictably inaccurate depth measurements when comparing the LAWM device and standard hand measurement 17. Differences in the LAWM device and dental paste measurement of volume most likely lie in the consistently inaccurate measurement of wound depth. In terms of absolute measurement for non‐standard wounds, the LAWM device in the ‘healing’ wound model tested showed a similar pattern of statistically significant differences in depth when compared with standard measurement techniques as in the previous study.

Some authors, however, have suggested that percentage wound reduction over time can be a robust predictor for wound healing and can be useful in the clinical setting as absolute measurements 24. Through the analysis of these percentage differences in both wound depth and wound volume over time, it is indicated that the LAWM device can be used to calculate these percent differences accurately with no statistically significant difference compared with standard measurements. Although occasionally inaccurate in its absolute measurement, the LAWM device can be a useful tool in the clinicians' arsenal as it reliably measures the rate of percentage change in depth and volume and offers a potentially aseptic alternative to traditional measurement technique.

Conclusions

The LAWM device should be further developed to improve absolute measurement accuracy, but the current generation of device indicates that the clinically relevant percent change in wound volume is measured accurately. The study authors included a hypergranulation state for each of the four wounds; however, as the LAWM device is not calibrated to measure hypergranulation, the results indicated unpredictable and inaccurate measurement. Further research is needed to further validate LAWM devices in the clinical setting when compared with standard methods of wound measurement.