The Evolving Field of Wound Measurement Techniques: A Literature Review

Objective. Wound healing is a complex and multifactorial process that requires the involvement of a multidisciplinary approach. Methods of wound measurement have been developed and continually refined with the purpose of ensuring precision in wound measurement and documentation as the primary indicator of healing. This review aims to ascertain the efficacies of current wound area measurement techniques, and to highlight any perceived gaps in the literature so as to develop suggestions for future studies and practice. Methods. Medline, PubMed, CliniKey, and CINAHL were searched using the terms “wound/ulcer measurement techniques,” “wound assessment,” “digital planimetry,” and “structured light.” Articles between 2000 and 2014 were selected, and secondary searches were carried out by examining the references of relevant articles. Only papers written in English were included. Results. A universal, standardized method of wound assessment has not been established or proposed. At present, techniques range from the simple to the more complex – most of which have characteristics that allow for applicability in both rural and urban settings. Techniques covered are: ruler measurements, acetate tracings/contact planimetry, digital planimetry, and structured light devices. Conclusion. In reviewing the literature, the precision and reliability of digital planimetry over the more conventional methods of ruler measurements and acetate tracings are consistently demonstrated. The advent and utility of the laser or structured light approach, however, is promising, has only been analyzed by a few, and opens up the scope for further evaluation of this technique. 

The accurate assessment and measurement of wounds is an important aspect in determining the efficacy of ongoing wound management therapies. A continued, objective analysis of wounds facilitates the prediction of healing. Though multifactorial in nature, the precise documentation of wound size and healing over time allows clinicians to gauge responses to treatment, thereby maximizing healing rates by tailoring interventions as required.^1,2 

Various techniques are utilized for the measurement of wounds in the clinical setting, ranging from the simple to the more complex. The suitability of the different modalities may differ in different clinical settings (eg, rural versus urban) and depend on institutional resources. However, as serial wound measurements are a reflection of healing potential,^1,2 the reliability and precision of each tool must be taken into account and scrutinized.

Studies have consistently demonstrated a correlation between percentage reduction in wound surface area and treatment outcome.^1,3-5 A reduction in wound area of 30% within 2 to 4 weeks of treatment was shown to be a suitable predictor of healing and a reflection of treatment efficacy.^3,4 An accurate function of healing is denoted by percentage, as opposed to absolute change in wound area.⁵ The initial rate of healing can be utilized to distinguish between a healing and non-healing ulcer.⁵ Such rates should not be projected or extrapolated to determine the time needed to complete healing due to the presence of other uncontrollable factors including accidental tissue trauma, infection, nutritional status, and other disease processes.^1,5,6 

 Hence, the importance of continuous wound assessment is emphasized as a tool to distinguish between effective and ineffective treatment regimes.^1,2,7,8 However, no gold standard or protocol exists to do so. A standardized method for the measurement of wounds, in the absence or minimization of operator variability and subjectivity, would allow for precise and reliable documentation that can be compared across different clinical settings. Plassmann et al⁹ identified further barriers for attaining more accurate wound measurements: 1) appropriate definition of the wound boundary, 2) wound flexibility in wounds that are undermined or deep, and 3) natural curvatures of the human body.

This review aims to ascertain the efficacies of current wound area measurement techniques for the clinical setting and to highlight any perceived gaps in the literature so as to offer suggestions for future studies or practice. 

Medline, PubMed, CliniKey, and CINAHL were searched using the terms “wound/ulcer measurement techniques,” “wound assessment,” “digital planimetry,” and “structured light.” Articles between 2000 and 2014 were selected due to the introduction of electronically assisted methods of wound measurement following the millennium, and secondary searches were carried out by examining the references of relevant articles. Only papers written in English were included. 

Ruler technique. The surface area of a wound can be approximated by multiplying the greatest length and perpendicular width measurements. The limitation of this simple technique is clear as wounds seldom take on defined geometric forms. Surface area measurements with this technique, though simple and accessible, are imprecise for irregular, large, and cavity wounds.¹ The same principle holds true in determining the volume of a wound where varying depth, potentially throughout the wound bed, cannot be accounted for precisely.

Studies have consistently shown that the ruler or linear method of surface area measurement overestimates the size of a wound by 10%-40%.^10-13 Flanagan¹ suggested clinicians use careful documentation of the points from which measurements are taken to improve the consistency and the accuracy of subsequent readings and changes in approximated size.

An alternative to the standard length x width measurement has been described with wounds taking on the shape of an ellipse. Surface area of such wounds can be measured using the following formula:

Area (mm²) = length (mm) x width (mm) x π x 0.25

Varying results have been described regarding the reliability of the elliptical formula for calculating wound area. Two small studies were carried out by Bowling et al¹⁴ and Shaw et al.¹⁵ Bowling et al¹⁴ (n = 76) compared manual approximation of wound size versus digital planimetry with results reflecting a strong correlation between the 2 techniques. The study dealt largely with ulcers < 5 cm², but they also acknowledged that discrepancies in area measurements increased with the size of a wound. Similar conclusions have been derived in other studies that have demonstrated diminishing reliability of ruler area measurements in wounds > 10 cm.^2,11,13,15 Shaw et al¹⁵ (n = 16) evaluated the use of the Visitrak system (System A; Smith and Nephew, Auckland, New Zealand), digital planimetry, and linear area measurement using the above formula. Statistically significant underestimation in wound size using the formula for an ellipse was noted for smaller wounds, of which the parameters were not defined. The authors¹⁵ acknowledged the limitations of the small sample size; not one method was held to be more superior to another in terms of accuracy or reproducibility.  

Acetate tracings and contact planimetry. The conventional method of wound tracing, much like the ruler method, is widely utilized in the clinical setting because it is inexpensive and accessible. It involves placing a transparent sheet across the wound surface and then tracing its margins with indelible ink. The surface area is then determined by placing the tracing over a grid and counting the number of squares within the circumscribed area. 

As the technique involves direct contact with the wound surface, several potentially significant disadvantages arise including damage and contamination of the wound bed, deformation to the wound shape and size, and pain and discomfort for the patient.¹⁶ Determining the surface area of a wound has been described as a 2-staged approach: first by precise identification of the wound edge and, second, allowing for calculation of area using either manual or digital means.¹ 

The term “planimetry” in this setting simply refers to an instrument used to measure the area of a given shape. Among the papers examined, this general term is utilized for both contact and non-contact (purely digital) planimetry. 

A 2014 study conducted by Bilgin and Günes¹⁰ examined the intraclass correlation coefficient (ICC) between 3 wound measurement techniques. Eighty pressure ulcers on 65 participants were measured by linear approximation, acetate tracing, and digital planimetry using System A. Ulcers were categorized into small and large groups with areas of < 10 cm² and > 10 cm², respectively.¹⁰ 

System A incorporates the traditional method of contact wound perimeter tracing with a digitized area measurement software. It involves contact tracing of the wound onto a transparent sheet, and retracing the outline onto a digital pad (dimensions 30 cm x 21 cm) that calculates the surface area. 

This method demonstrated strong agreement among the 3 techniques particularly for smaller, more regularly shaped wounds (ICC = 0.95), and only modest agreement for the larger, more irregularly shaped wounds (ICC = 0.7). Findings supporting this result were presented in 2 separate studies by Oien et al¹¹ and Gethin and Cowman,¹⁶ of which 50 wounds were analyzed in each. Both research studies sub-grouped wounds into “small” and “large” sections by the same parameter. Similar methods of linear measurements, contact planimetry, and grid-counting were employed. High levels of agreement were present between the different modalities in ulcers up to 10 cm,^2,11,16 with discrepancies in area measurements increasing with the size of the wound with the ruler method.¹⁶ As such, Oien et al¹¹ established superiority of square-counting and contact planimetry over linear approximations. Both studies ascertained suitability of both square-counting and contact planimetry (System A) methods.

Non-contact planimetry. In contrast to System A, non-contact digital planimetry does not involve contact with the wound surface. The use of non-contact planimetry has been described in several studies.^15,17-20 A target plate or scale gauge is placed in the same plane as the wound. An image is captured with the use of a high-resolution camera and uploaded onto a computer. Digital image analysis is undertaken by specialized software (VeV Measurement Documentation [System B], Vista Medical, Winnipeg, Canada; and PictZar [System C], Elmwood Park, NJ) once the wound margin has been outlined on the computer by the observer (Figure 1). 

Comparative studies between wound contact tracing and digital planimetry exist with the use of simulated wounds and pressure ulcers in the clinical setting. Samad et al¹⁷ carried out their study in 2 phases: first by assessing the accuracy of both techniques with the use of elliptical cutouts of known size; and second, in the setting of a vascular surgery clinic, 25 venous leg ulcers were assessed by 4 different observers. Measuring the area using reference shapes showed an underestimation of actual area by 3.9% that was statistically significant with the use of contact tracing; however, overall accuracy was deemed acceptable. Interobserver reproducibility was good for both contact and non-contact techniques in the simulation and the clinical settings (correlation coefficient > 0.8). The authors concluded digital planimetry was the more accurate of the 2 methods; however emphasizing the importance of high quality images so as to suitably define wound margins. It was also noted that the time taken to perform measurements was positively correlated with the area size when contact tracing was used. Digital measurements were less time dependent.  

Thawer et al¹⁸ compared the use of digital planimetry (using System B) and contact planimetry. The study involved 45 human and 38 animal wounds that were each traced 3 times, both on the subject and on the computerized software. Wounds that could not be captured in a single image were excluded from this study. Both techniques were deemed to be reliable and precise, though lower standard error of measurement (SEM) scores were attained with digital planimetry, notably with the smaller animal wounds. Interrater and intrarater improved across the board when an average of the 3 measurements was used. 

In a comparison study, Haghpanah et al¹⁹ compared similar techniques using Systems A and B; they evaluated the systems with the use of 2-dimensional cardboard cutouts of the known area (or premeasured areas despite irregular dimensions to use as a control).¹⁹ In this study, 40 wounds were measured twice by 4 observers using the above techniques (including linear measurements). The accuracy of the techniques was determined by the root mean square error where a smaller result portrayed a more precise technique. Using Systems A and B attained comparable results across large and small wounds. Interrater variability was significant for both techniques when wound size was not taken into account. System B showed greater accuracy for larger wounds whereas the obverse was true for smaller wounds. Though not formally assessed in this study, the observers highlighted the time-consuming nature of contact planimetry using System A for the large wounds. The study was carried out in a controlled setting with simulated wounds and stressed the importance of camera angulation and orientation in relation to the wound.

Wendelken et al’s²⁰ large study (n = 200) assessed wound areas as calculated by acetate tracings and digital planimetry. Their results complimented Samad et al¹⁷ with both intrarater (98.3% versus 89.3%) and interrater reliability (94% versus 84%) shown to be superior with digital imaging, where wound borders can be more accurately defined and larger wounds more objectively assessed. This review of the literature and the studies involved have plainly highlighted the benefits of non-contact, digital planimetry. The relative accuracy, reliability, and advantages of this non-contact method has shown to be practical in the clinical setting given the availability of resources. 

However, despite the ease of clinical application of non-contact digital planimetry, limitations exist — inherent limitations attributed to the technique itself and operator-dependent variations. The natural curvature of the body, and hence wound surfaces, is difficult to account for and is acknowledged in the literature.^1,2,7,17,21 Furthermore, some wounds may not be able to be captured completely in a single image. The structured light approach, discussed later, takes this into account. 

An element of subjectivity may exist in each assessor’s ability to accurately delineate wound borders. Discrepancies however can be diminished in several ways. The literature suggests that accuracy can be improved by the use of a common assessor for each patient.^1,18 Collecting multiple measurements and attaining the average of the results has also been postulated as another means to improve measurement precision.¹⁸ The use of more experienced members of staff may also be beneficial in the appropriate identification of wound epithelialization and borders. 

Wound epithelialization and contraction occur as part of the natural processes of wound healing and are part of the proliferative and remodelling phases, respectively.⁶ The ability to accurately ascertain wound boundaries and epithelialization plays an important role in continued wound measurements. Optimization of this involves appropriate debridement of the wound surface so as to remove blood and exudate that may confound the borders and hence, tracings of the wound, either by contact or digital means. The importance of this extends to clinical practice where adequate preparation of the wound bed prior to dressing changes diminishes factors that may impede wound healing.

Few studies have been conducted on the use of the structured light or laser approach to wound measurement. It is a noncontact technique that involves the collective use of a digital camera and projected laser beams that distort with the curvature, depth, and irregularity of a wound surface. The mechanism creates a topographical model of the wound using 2 captured images with differing positions of the laser beams. The images are captured onto a mobile computing device where the operator outlines the wound perimeter thereby allowing for calculation of wound area and volume. The mechanism incorporates digital planimetry, while having an additional specification that allows it to measure the curvature of the body along which the wound lies.

Hammond and Nixon²² assessed the intrarater and interrater variability by using the SilhouetteMobile™ (System D; ARANZ Medical, Christchurch, New Zealand). The study recruited 3 operators with varying lengths of clinical use on the device — ranging from no experience to a couple of months. Multiple measurements of 5 wounds from 5 different patients in an outpatient wound management clinic were recorded. The ICC across the board depicted consistencies in the measurement of area and depth with values of 0.998 and 0.990, respectively. Low intrarater and interrater coefficients of variance were reported with measurement of wound surface area.

Miller et al²³ further assessed System D, and they found results similar to Hammond and Nixon.²² The ICC values (0.92) depicted reliability of readings attained by 7 clinicians across 14 wound images; this value increased to 0.988 when averaging 3 repeated measurements. The accuracy of the device as compared to other measurement techniques was not investigated (Figure 2). 

Davis et al²⁴ independently assessed the validity of the surface area and volume measuring capabilities of SilhouetteStar™ (System E; ARANZ Medical, Christchurch, New Zealand) against digital planimetry (ImageJ [System F], National Institutes of Health, Bethesda, MD), ruler depth measurements, and a volume assessment with the use of dental paste. The dental paste mold was utilized as a control for wound volume in the first phase of the study. System E operates in a similar fashion to System D but it uses 3 laser beams instead of 2. All measurements including volume and depth are calculated with a single image capture. System E’s mechanism of volume measurement was not elaborated upon. Surface area calculations from System F were multiplied with ruler depth measurements to attain approximate volumes of the wounds analyzed in Davis et al.²⁴ 

The study was carried out in 2 phases with initial assessments made on 12 artificially crafted porcine wounds. Following this, 16 artificial cylindrical wounds were created, each with identical surface areas and progressively decreasing depths to mimic the gradual healing of a wound. 

Area, wound depth, and wound volume comparisons were made using the aforementioned techniques with the following results. Statistically significant differences in surface area measurements between the 2 software programs (Systems E and F) were depicted in 4 of the 12 cadaver wounds, all with differences of less than 15%. This is in contrast to the discrepancies recorded in the second phase of the trial using models with a fixed surface area where no significant measurement differences were noted across the 16 specimens. System E however demonstrated consistently lower depth readings in both the porcine and constructed wounds. 

In the second phase of the study, the authors²⁴ attained the depth ratio between the System E and ruler measurements as a function of the controlled wound depths. A line of least regression was fitted into this model, with a low coefficient of determination (R²) of 0.00118 reflecting that the varying ratios are independent of wound depth. The second phase of the Davis et al²⁴ study was integral in concluding that the lower readings attained with depth and hence volume using System E were consistent and predictable. Assessment of wound healing utilizing percentage changes in area or volume can therefore still be relied upon with this device. 

Further evaluation of volume measurements utilizing dental paste molds delineated statistically significant differences across all 12 porcine wounds when compared to the volume data from System E. Artificially lower depth and volume measurements were consistently reflected in System E’s readings. Differences in volume readings against System F multiplied by ruler depth measurements were not significant however. 

The superiority of digital planimetry over the more conventional methods of ruler measurements and acetate tracings has been consistently demonstrated. However, few have analyzed the utility of the laser or structured light approach. Further evaluation of this technique is required. Yet to be explored is the repeatability or interrater variability as a function of System E. Its advantages are similar to that of digital planimetry, with the use of a noncontact technology that allows for measurement and photographic documentation of the wound and its potential practicality in remote settings and telemedicine.

The importance of continued wound assessment particularly within the initial 2 to 4 weeks of treatment has been highlighted by a number of studies. Reduction in area of 20% to 40% within this time is an accurate predictor of healing. Accurate modalities of wound measurement need to be incorporated into practice for conclusions to be drawn regarding the efficacy of concurrent wound treatments.  

A universal, standardized method of wound assessment has not been established or proposed. The move towards a measurement technique that minimizes inter-observer subjectivity, accounts for anatomical variations, and allows for sequential wound assessment and documentation would be beneficial in the clinical setting. Although an element of subjectivity may be present in establishing the extent of epithelialization and demarcation of wound borders, studies have highlighted the utility of repeated measurements in contributing to more reliable readings. 

No large or multihospital studies have been performed to assess the accuracy and reliability of the newer, digitalized techniques. However, the precision and reliability of digital planimetry over linear measuring methods have been supported across the board. Advantages of non-contact techniques are clear. Though more expensive to integrate into the clinical setting, they eliminate the risk and potential additional costs of wound contamination and damage. Such methods avoid placing the patient in a position of discomfort and allow for continuous visual documentation of the wound. If the practicality and accuracy of these newer devices can be ascertained through further studies, a gold standard in wound assessment and measurement may be realized. 

Wound healing is a complex and multifactorial process that requires the involvement of a multidisciplinary approach. The precise measurement of wounds will facilitate the predictive value of wound healing and assess treatment efficacy that will ultimately result in positive patient outcomes. 

From the Department of Vascular Surgery, Sir Charles Gairdner Hospital, Perth, Western Australia

Address correspondence to:
Rachel Khoo, MBBS, GradDipAppAnatDiss
Sir Charles Gairdner Hospital
Hospital Avenue,
Nedlands, WA, Australia 6009
rachelkhoo@hotmail.com.au

Disclosure: The authors disclose no financial or other conflicts of interest.