Title: An Evaluation of Three Wound Measurement Techniques in Diabetic Foot Wounds 1 An Evaluation of Three Wound Measurement Techniques in Diabetic Foot Wounds Julia Shaw, BSc1 Ciara M Hughes, PhD2 Katie M Lagan, DPhil2 Patrick M Bell, MD FRCP3 Michael R Stevenson, BSc Fss 4 1 Regional Centre for Endocrinology and Diabetes, Royal Hospitals, Belfast, Northern Ireland 2 University of Ulster, Newtownabbey, Belfast, Northern Ireland 3 Regional Centre for Endocrinology and Diabetes, Royal Hospitals, Belfast, Northern Ireland 4 Medical Statistics, Epidemiology and Public Health, Queen’s University, Belfast, Northern Ireland Corresponding Author: Professor Patrick M Bell East Wing Office, Royal Hospitals Grosvenor Rd, Belfast BT12 6BA. Northern Ireland. Email: Patrick.bell@royalhospitals.n-i.nhs.uk Received for publication 19 January 2007 and accepted in revised form 21 June 2007. Additional information for this article can be found in an online appendix at http://care.diabetesjournals.org. Diabetes Care Publish Ahead of Print, published online June 26, 2007 Copyright American Diabetes Association, Inc., 2007 2 Approximately 80% of diabetes- related amputations are preceded by a diabetic foot ulcer (1-2). Wound measurement is an important component of successful wound management (3-6). Accurate identification of the wound margin and the calculation of wound area are crucial (7-9). Although more complex methods of wound measurement exist (planimetry, digitising techniques and stereophotogrammetry) (4,10-14), current practice focuses on wound measurement using simple ruler-based methods or by wound tracing. Ruler- based schemes tended to be less reliable in wounds >5cm2 (11). Various mathematical formulae (including the calculation of area based on the formula for an ellipse) have been proposed to improve accuracy in wound surface area calculation in wounds <40cm2 in size (10,11,15-17). The aim of this study was to evaluate and compare three wound measurement techniques: the Visitrak system (Smith and Nephew Healthcare Ltd., Hull), a digital photography and image processing system (IP) (Analyze Version 6.0. Lenexa, Kansas, US) and an elliptical measurement method using the standard formula (πab) for the calculation of the area of an ellipse. Research Design and Methods Patients (n=16) with neuropathic and neuroischaemic diabetic foot wounds were recruited from the Diabetic Foot Clinic in the Royal Hospitals Trust, Belfast. Ethical obligations were fulfilled and patients received standard multi-disciplinary care. Validity and repeatability within each method were investigated and determined by measuring images of a known size 20 times each. Repeatability and comparability were considered between each method of measurement on the wounds. Each wound was traced and measured a total of 9 times; wound surface area was calculated in mm2 and means and standard deviations calculated. Statistical Analysis Validity was analysed using a 1-sample t- test. Repeatability within each wound measurement method was investigated by calculating a coefficient of variation (CV) for each wound measurement. Using SPSS (Version 11.0 for Windows), the Friedman’s test was used to determine if any one method was consistently more repeatable than another. In order to compare wound measurement between the methods, a mean wound size was calculated for each wound using each measurement method, a logarithmic conversion of the data was performed, and an Analysis of Variance (ANOVA) was used to complete a calculation of comparability. A Bland and Altman Plot supported by a paired t-test were used to examine differences between the elliptical and Visitrak methods. Results Validity varied across the three methods but was deemed to be acceptable overall (Table 1). The Visitrak method measured images <25mm2 inaccurately (p<0.001), and the elliptical method tended to under- estimate size in small wounds (p<0.001). 3 The IP method was advantageous in allowing unique calibration of each image, and so eliminated subjective wound tracing. The method was repeatable. The main disadvantage was that validity of this method was questionable. The mean CV (n=46) for all wounds was calculated as 7.0 (Visitrak), 4.7 (IP) and 8.5 (Ellipse) indicating that repeatability was acceptable overall. Freidman’s test indicated that no one measurement method was consistently more repeatable than another (p=0.15). Elliptical wound measurement had some of the advantages of the Visitrak method (tracings were quick, easy, inexpensive and non-invasive to perform). The main disadvantages described in using ruler- based mathematical methods are that they have been shown to over-estimate wound area by 10-25% (16,18) in wounds >5cm2. By contrast, in this study the elliptical method of measurement was shown to under-estimate wound size in smaller wounds (p<0.001) compared to the other two methods. Analysis of comparability indicated that there were some differences between the three methods. Graphical analysis reported 3 outlying values (both high and low) using the IP method and so wound measurement could be inaccurate either way compared to the other two methods. Differences were shown between the Visitrak and Elliptical methods when analysed alone (t-test = -2.72, p=0.017). This study does have limitations. The sample size was small and conclusions can only be drawn for a specific type of wound. There is no gold standard method of wound measurement. The authors conclude that the elliptical method is a suitable measurement tool for use in studies investigating diabetic foot wounds as it is simple, inexpensive, valid, repeatable and easy to use. Discussion The main advantages of the Visitrak method were that the tracings were quick, easy, inexpensive to perform and non-invasive for the patient. Foot curvature was considered and the subjectivity associated with manual square counting was removed. The method was both valid and repeatable in the measurement of wounds >25mm2 in size. The main disadvantages were the inability to measure small wounds of <25mm2 accurately (p<0.001). When compared to the other methods, the Visitrak method tended to underestimate wound size and statistical significant differences were found (p=0.017) when compared to the elliptical method alone. Acknowledgements We wish to thank Dr RJ Winder, Director of the Health and Rehabilitation Sciences Research Institute, University of Ulster, Newtownabbey, Belfast, for his expertise and assistance with the IP System. 4 References 1. Pecoraro RE, Reiber GE, Burgess EM: Pathways to diabetic limb amputation: basis for prevention. Diabetes Care 13:513-521, 1990. 2. McNeely MJ, Boyko EJ, Ahroni JH, Stensel VL, Reiber GE, Smith DG, Pecoraro RF: The independent contributions of diabetic neuropathy and vasculopathy in foot ulceration: how great are the risks? Diabetes Care 18: 216-219, 1995. 3. Oyibo SO, Jude EB, Tarawneh I, Nguyen HC, Armstrong DG, Harkless LB, Boulton AJM: The effects of ulcer size and site, patient's age, sex and type and duration of diabetes on the outcome of diabetic foot ulcers. Diabetic Medicine, 18, 2: 133-138, 2001. 4. Flanagan M: Wound Measurement: can it help us to monitor progression to healing? Journal of Wound Care, 12, 5: 189-194, 2003. 5. 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Lagan KM, Dusoir AE, McDonagh SM, Baxter D: Wound Measurement: The comparative reliability of direct versus photographic tracings analyzed by planimetry versus digitising techniques. Arch Phys Med Rehabil, 81:1110-1116, 2000 13. Langemo, D. K, Melland H., Hanson D, Olson B, Hunter S, Henly S. J: Two- dimensional wound measurement: comparison of 4 techniques. Adv.Wound.Care, 11, 7: 337-343, 1998. 14. Melhuish JM, Plassmann P, Harding KG: Circumference, area and volume of the healing wound. Journal of wound care. 3, 8:380-384, 1994. 5 15. Johnson JD: Using ulcer surface area and volume to document wound size. J.Am.Podiatr.Med.Assoc, 85, 2: 91-95, 1995. 16. Goldman RJ, Salcido R: More than one way to measure a wound: an overview of tools and techniques. Advances in Skin and Wound Care, Sept/Oct :236-242, 2002. 17. Mayrovitz HN: Shape and area measurement considerations in the assessment of diabetic plantar ulcers. Wounds, 9, 1: 21-28, 1997. 18. Majeske C: Reliability of wound surface area measurements. Physical Therapy, 72, 2: 138-141, 1992. 6 Table 1. Summary of results reported on the validity and repeatability of 3 wound measurement methods in diabetic foot wounds. Validity/ Reliability Repeatability Definition (in relation The ability of an instrument to measure what it is supposed to measure (wound The ability of the same operator using the same to wound measurement) area) in a precise way over a short period of time. instrument to measure the same wound over a short period of time repeatedly Statistical Analysis 1-sample t-test on images of a known size Coefficients of Variation (CV’s) calculated for each wound measurement method Freidman’s test used to determine if one method was consistently more repeatable than another Method Image of a known size (mm2) Mean area measured by each method (mm2) % difference p-value Calculable CV’s for wound area measured by each method Visitrak 25 19.5 -22.0 <0.001 100 98.5 -1.5 =0.27 Mean CV 7.0% 1600 1580.5 -1.2 =0.06 IP 20 20.02 +0.1 =0.64 Mean CV 4.7% 20 20.01 0.0 =0.73 Elliptical 37 34.3 -7.3 <0.001 p-value 883 883.0 0.0 =1.0 Mean CV 8.5% p=0.15 5361 5338.2 -0.4 =0.26 A Results p-value