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Comparison of 3-dimensional Wound Measurement With Laser-assisted and Hand Measurements: A Retrospective Chart Review

Empirical Studies

Comparison of 3-dimensional Wound Measurement With Laser-assisted and Hand Measurements: A Retrospective Chart Review

Index: Wound Manage Prev. 2019;65(1):36–41.

Abstract

Wound area measurements provide an objective assessment of wound healing; however, most commonly used measurement techniques are imprecise. Purpose: A new portable 3-dimensional (3D) wound measurement device was tested against laser- and hand-measurement methods. Methods: A retrospective comparative analysis was conducted to analyze the difference in wound measurements using records of patients seen at the University of Miami Hospital (Miami, FL) outpatient wound healing clinic between November 2017 and February 2018 who had wounds of various etiologies measured using 3 different techniques during a single visit: the 3D device, a laser-assisted wound measurement device (laser), and standard hand measurements. Patients with circumferential wounds were excluded (the laser and 3D devices are incapable of assessing these wounds). Differences were compared using paired t tests. Results: The wounds ranged in area from 0.8 cm2 (hand measurements) and 0.2 cm2 (3D and laser devices) to 100.94 cm2, 61.9 cm2, and 65 cm2 by hand measurement, 3D, and laser device, respectively. Among the 23 wounds measured, the majority (16) were venous ulcers. No statistically significant difference was noted between the 3D measurements compared with the laser (P = .340). Statistically significant differences in the measurements between the 3D device and hand measurements (P = .008) and the laser device and hand measurements (P = .006) were found. Conclusion: Measurements of the 3D device appear analogous to laser devices, making it an alternative tool for clinicians interested in monitoring wound progression. Because the 3D device has the capacity to examine wound volume, prospective comparative trials should be used to examine the accuracy and precision of the device to measure volume.

Introduction

Ulcers represent 1% of all skin disease diagnoses, presenting a significant medical and economic burden.1 Wounds are the most expensive skin condition; more than $11 billion is spent annually on the management of chronic and acute wounds.1 To limit these costs, practitioners must determine whether the therapies they are prescribing are effective, so money is not wasted on ineffective treatments. Wound area measurement is the primary objective assessment for wound healing.2 Percent wound area reduction has been shown to be a valid predictor of healing of diabetic foot ulcers, pressure ulcers and venous leg ulcers.3-6 In a 12-week prospective trial involving 203 patients with diabetic foot ulcers, Sheehan et al4 demonstrated that patients with greater percent wound area reduction at 4 weeks had a significantly higher chance of complete healing. In prospective descriptive study, van Rijswijk et al6 showed in a population of 48 patients that percent reduction in pressure ulcer area after 2 weeks was predictive of healing. A multicenter cohort study of 104 patients with venous leg ulcers by Kantor et al5 demonstrated percent change in area reduction after 4 weeks of treatment was predictive of complete healing at 24 weeks. 

Wound measurements help clinicians better understand the prognosis of the patient’s condition and assess the efficacy of ongoing wound therapies. A randomized clustered trial of 74 wound centers by Kurd et al7 demonstrated that providing prognostic information based on wound size and wound area reduction after 4 weeks improved the rate of wound healing in diabetic and venous leg ulcers at 20 and 24 weeks, respectively. 

The tools used for wound assessments are limited. Various techniques have been employed to measure wounds, each with strengths and weaknesses. The ruler technique involves manually measuring length and width, then calculating surface area. Planimetry, either contact or noncontact, consists of reproducing the perimeter of the wound on a surface and then measuring the area.8,9 Laser-assisted wound measurement devices are newer tools that can additionally measure wound depth (3 dimensions [3D]).8 This is important, because reduced wound depth has been shown in prospective randomized trials10,11 to be an early indication of healing in deeper wounds.

Despite the variety of wound measurement instruments available, there is no valid, reliable, widely used method (ie, gold standard). An ideal measuring technique should yield standardized, accurate measurements with the use of a portable, fast, and easy-to-use device (see Table 1). A new 3D wound measurement device (eKare inSight®; eKare Inc, Fairfax, VA) represents a convenient alternative measurement system that has been validated in artificial wound models, animal models, and diabetic foot ulcers.12-14 Sheng et al13 compared this 3D device to planimetry in 46 wounds in 7 rats; no significant difference was noted in wound measurement. In a pilot study by Bills et al,14 the 3D device was compared to a laser-assisted wound measurement device in 7 wound models and demonstrated accuracy similar to Sheng et al.13 However, the validity and utility of 3D measurement in the context of clinical treatment of multiple wound etiologies has yet to be documented. 

The purpose of this retrospective study was to compare the 3D device to a laser-assisted wound measurement device (Silhouette Star; Aranz Medical, Christchurch, NZ) and to hand measurements obtained from wounds of various etiologies. The laser device was chosen for comparison because it has been validated in multiple studies and used in a variety of clinical trials.15-18 Hand measurements also were compared to the 3D and laser devices due to their simplicity and ubiquity in wound healing clinics3; large percent reductions in hand measurements are considered predictive of wound healing per multiple studies.4,19 

Materials and Methods

The 3D device consists of an infrared-based structure sensing camera similar to a portable Microsoft Kinect(an accessory for Xbox One, Microsoft Corp, Redmond, WA) that is fitted to a tablet (iPad; Apple, Cupertino, CA). The device is associated with an integrated HIPAA-compliant cloud server. 

On the tablet, the user first encircles the wound image on the tablet (including surrounding healthy skin) to delineate the region of interest on the depth map, which is transformed into a 3D space. Then, with a single finger swipe, the user specifies a reference point on the wound and on a nonwound area; these points will function as seed regions for device interpretation. The device then automatically traces the wound perimeter. The segmentation result is displayed in real-time using the interactive Graph Cuts algorithm implemented by Boykov et al.20 Subsequently, a 2-dimensional image with depth values can be transformed into a 3D surface using the intrinsic camera parameters of the sensor. This facilitates measurement of wound length, width, depth, perimeter, area, and volume. 

 The laser takes a picture at a standardized distance from the wound; the user then manually delineates the wound edge using the computer, generating a wound area measurement. The same laser device was used across all participants.

Hand measurements were taken by trained wound research fellows. A metric ruler was placed adjacent to the wound and the area was calculated by multiplying the orthogonal longest length and width. The validity and reliability of each method is addressed in the discussion.

Medical records for patients seen at the University of Miami Hospital (Miami, FL) in the outpatient wound healing clinic between November 2017 and February 2018 were obtained. Patients whose wounds were measured at the same visit with all 3 wound measuring techniques (3D device, laser device, and hand measurements) were identified (no participants had their wounds measured using all 3 methods more than once during the study period). Patients with circumferential wounds were excluded because the laser and 3D devices are incapable of assessing these wounds. Demographic data including age, gender, and race and wound type  and wound area measurements using the 3 techniques were extracted from the chart, collected on Excel spreadsheets, and entered to the statistical analysis system (SPSS Statistics; IBM, Armonk, NY) for analysis. The purpose of these measurements was not only to determine if the 3D device had accurate results in comparison to a validated and trusted measurement device (laser). SPSS also was used to construct a Bland-Altman plot to determine the absolute and percent difference in wound area measurements and to apply paired t tests to determine statistical significance. Paired t testing was used rather than analysis of variance because the authors’ primary comparison was between the 3D device and the laser device. This study was approved by the Institutional Review Board at the University of Miami. 

Ethical considerations. The study was approved by the Institutional Review Board of the University of Miami. The author(s) complied with the guidelines for conducting research in human subjects.

Results

Nineteen (19) patients met the inclusion criteria, providing a total of 23 wounds of various etiologies (see Table 1). The wound area of the various lesions ranged from 0.8 cm2 by hand measurement and 0.2 cm2 by the 3D and the laser device to 100.94 cm2, 61.9 cm2, and 65 cm2 by hand measurement, 3D, and the laser device, respectively (see Table 2).

The average absolute difference in wound area measurement between the 3D device and the laser device was 0.33 cm2. Taking into consideration the total area of the wounds, this accounted for an average of 3.88% difference in wound area measurements. In contrast, the average absolute difference in area between the 3D device and hand measurements was 4.74 cm2, a 32.55% difference. The average absolute difference between hand measurements and the laser device was 4.60 cm2, a 32.79% difference. Using paired t tests, no statistically significant difference was found in measured area between the 3D and the laser devices (P = .340). The Bland-Altman plot comparing percent difference in wound area measurement to wound area for the 3D and laser devices is illustrated in the Figure.21 Statistically significant differences in area were noted between both the 3D and the laser devices in comparison to hand measurements (P = .008 and P = .006, respectively) (see Table 3). 

One (1) wound was significantly larger than the others (wound 6), leading to some concern of an outlier bias. With this outlier removed, the difference in area measured between the 3D device and the laser remained statistically insignificant (P = .886). Hand measurements significantly differed from the measured areas of both the 3D and laser devices (P < .001) (see Table 3).

Discussion

Each method of wound area measurement has its own strengths and weaknesses. According to a prospective, comparative trial22 of hand measurements using standardized wound models with known area, hand measurements are fast, inexpensive, and can accommodate circumferential wounds, but they are also inaccurate, imprecise, and risk contamination of the wound. In addition, the many ways to measure wound area by hand adds to the imprecision. Some practitioners multiply the largest length and width of the wound regardless of orientation, while others take the longest length and the longest perpendicular width; the longest width head-to-toe and the longest width side-to-side also can be measured.22 All of these methods overestimate wound area because they assume that wounds are perfect squares or rectangles.22 A retrospective analysis23 of 2768 wounds demonstrated that hand measurements overestimated wound area by 44%. Large wounds and irregularly shaped wounds exacerbate the inaccuracy.3 This measurement technique is considered to be simple but not very reliable for irregular or large wounds.3 Although research is limited in this area, it seems plausible that when patients have irregular wounds, hand measurements may be insufficient to accurately measure percent area reduction.

Acetate tracing is another low-tech method of wound measurement. A 2-layer, transparent sheet with a square centimeter grid is placed on top of the wound, and the border is traced; the area inside the border then can be calculated by square counting.24 Digital planimetry works the same way but requires retracing the wound onto a tablet computer, which then calculates the wound area.24 The advantages of this system are relatively accurate and precise wound measurements. However, it can be a time-consuming procedure, and the results can vary slightly based on the subjective interpretation of the wound border, the use of excessively thick markers, or the use of too much pressure on the wound, which can alter the outline.24 Additionally, according to literature reviews,8 acetate tracing may damage or contaminate the wound bed and may be painful. 

In noncontact planimetry, a target scale is placed in the same plane as the wound and a high-resolution photo is taken, after which specialized software analyzes the wound area based on the captured image.8 In a comparative trial25 of digital planimetry versus contact tracing of 11 shapes using 4 observers, the 2 techniques demonstrated similar wound measurement accuracy with a correlation coefficient of >0.8. Although noncontact planimetry is clinically expedient in comparison to contact planimetry, it has limitations. The technique cannot account for the natural curvature of the body, subjecting larger wounds to inaccuracies, and in larger circumferential wounds, the entire wound may not be able to fit within the confines of a single photograph.8 

Laser-assisted wound measurement devices are relatively new but attempt to improve upon noncontact planimetry by using both a digital camera and projected laser beams. This allows measurement of the curvature, depth, and irregularity of a wound surface. An initial picture is taken, and the operator outlines the wounds. The system then can calculate wound area and volume. The laser device used in the current analysis has been validated (average interclass correlation coefficient of 0.988) for interrater reliability in a study17 of 7 nurses involved in wound care. The device’s measurements also were validated for wound area and wound volume in 12 wounds on a porcine model18 and for area and volume measurements on clay models of diabetic wounds.16 It also has been trusted for multiple Phase I to Phase IV clinical trials, including multicenter and multinational studies.15 Laser-assisted measurements have distinct benefits: they have the potential to be more accurate than noncontact planimetry because they take into account the curvature of the body and can measure both wound volume and area.8 However, the overall process is more time consuming than hand measurements and requires bulky peripherals such as the laser device itself and computers for assessment. Additionally, this device is not able to calculate circumferential wounds because the entire wound cannot fit within the confines of a single photograph. 

The 3D wound measurement device used in this study has been validated in artificial wound models, animal models, and diabetic foot ulcers12-14 but had not been examined for use in other wound types. The interrater reliability of the device is considered to be high; in a study by Anghel et al,12 45 wounds were previously assessed by 2 raters using the 3D device with an interclass correlation coefficient of 0.998 for wound area.

 In the current study, both devices showed significant differences in area in comparison to hand measurements in a patient population with multiple wound etiologies including pyoderma gangrenosum, venous leg ulcers, diabetic foot ulcers, and traumatic ulcers. This is not surprising given the anecdotally high level of inaccuracy of hand measurements. No significant difference was found between the measurements obtained using the 3D device and the laser device, suggesting the 3D device exhibits similar accuracy for wound measurement in comparison to laser devices in a clinical setting. 

This accuracy is important in the clinical setting because wounds with irregular borders are difficult to measure accurately with hand measurements, making calculations of percent area reduction unreliable. Additionally, the 3D device is quick and efficient in clinical settings. Anecdotally, the device was found to have a friendly user interface that requires minimal training. Instead of outlining the wound directly, the user simply needs to broadly circle the wound so the software can algorithmically determine healthy versus wound tissue. This process anecdotally is fast in comparison to noncontact planimetry or laser devices. Previous wound measurements are easily accessible to trace the patient’s progress over time. Additionally, the information can be automatically synced with the product’s HIPAA-compliant cloud server, allowing the physician to access this data anywhere. Another advantage is mobility; a clinician can carry the tablet in a lab coat to each clinical encounter. However, the 3D device has important limitations. It captures a single image so it is unable to measure large circumferential wounds. Additionally, the device cannot take into account wounds with significant undermining. In cases of wounds with substantial undermining, various hand measurement techniques can be used to determine undermining depth. 

Limitations

This study has several limitations, including its retrospective design, small sample size, and potentially intrinsic differences in how measurements are obtained among device users. However, in this study, all members of the team were trained wound fellows, and the expected variability was low. Additionally, the laser device is considered to be an accurate and reliable measurement system, but all forms of measurement are subject to some variability. Additionally, the Bland-Altman plot only looks at agreement between 2 measurement techniques and does not require a “correct measurement” to determine agreement. Although the devices used in this study have the ability to measure wounds using 3D technology, only wound area measurements were used, because percent wound area reduction is the validated predictor of wound healing.3-6 Additionally, in previous studies18 the laser device was shown to consistently underestimate wound depth, making it a poor comparator. 

Conclusion

The purpose of this retrospective study was to compare the accuracy of wound area measurements among a 3D device, a laser device, and hand measurement. The results demonstrated no statistically significant difference in wound area measurements between the 3D device and the validated laser device, and both were more accurate than hand measurements, suggesting that clinicians can use the 3D device to determine percent wound area reduction (a validated marker of wound healing) with equivalent accuracy to the laser device and greater accuracy than hand measurements, particularly with wounds with irregular borders. Future prospective comparative trials of the 3D device are needed to assess the accuracy of the device for wound volume measurements for a variety of different wound etiologies. 

Disclaimer

The authors acknowledge that eKare Inc (Fairfax, VA) provided the research team with the 3D device used in the study.

Affiliations

Mr. Darwin, Dr. Jaller, and Dr. Hirt are wound research fellows; and Dr. Kirsner is a Harvey Blank Chair in Dermatology, Department of Dermatology and Cutaneous Surgery, University of Miami Miller School of Medicine, Miami, FL.

Correspondence

Please address correspondence to: Evan Darwin, 1600 NW 10th Avenue, RMSB 2023, Miami, FL, 33136; email: exd166@med.miami.edu.