Volume Measures Using a Digital Image Analysis System are Reliable in Diabetic Foot Ulcers
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Index: WOUNDS. 2012;24(6):146–151.
Abstract: Reliable measures of wound size are critical to wound healing research and clinical management. Measurement of full-thickness wounds is increasingly being done using digital images and photogrammetric software, such as VeVMD (Vista Medical, Winnipeg, Manitoba, Canada), to estimate wound volume. The reliability of VeVMD in determining wound volume is unknown. The present study sought to examine the reliability of wound volume measurements obtained using VeVMD. Methods. A cross-sectional study of adults with full-thickness, neuropathic, diabetic foot ulcers (DFU) at 2 sites in the US Midwest was undertaken. Ulcer images were obtained, stored, and used to obtain measures of wound volume using VeVMD. Four raters independently completed wound measures, and then repeated these measures 2 weeks after the first measurement. Raters were blinded to the comparison measurements. Inter- and intra-rater correlations were computed.
Results. Thirty-three enrolled subjects with 33 DFU were included in the analyses. Inter-rater reliability was 0.745 and intra-rater reliability was 0.868. Four ulcers showed noticeably less agreement between raters; these ulcers had small, but deeply recessed areas, resulting in differences in defining the wound margin. When these 4 ulcers were removed, inter- and intra-rater reliabilities were excellent (0.970 and 0.981, respectively). Conclusion. Reliabilities of volume measurements obtained with VeVMD were acceptable in DFU, even when raters had different definitions of the ulcer margin or changed their definition from time to time. However, conclusions cannot be drawn regarding the performance of VeVMD in other wound types.
The ability to obtain reliable measures of wound size is a critical component of wound healing research and clinical wound management. Compared to measures of surface area and circumference, measures of volume provide a more complete reflection of wound healing progress in full-thickness wounds.1Although several techniques are available for measuring volume, such as stereophotography,2 Kundin device,3-5and alginate molds,6 measurement of full-thickness wounds healing by secondary attention is increasingly being done using digital images of the wound and photogrammetric software that estimates wound volume since it is less invasive and complicated than other techniques.7 VeVMD (Vista Medical, Winnipeg, Manitoba, Canada) is a proprietary, computerized technique that is relatively easy to use, and does not require direct contact with the wound. However, the reliability of VeVMD in determining wound volume remains unknown.
The reliability of a measurement technique concerns the extent to which it yields consistent results with repeated measurement.8 Dimensions of reliability pertinent to computerized techniques to obtain measures of wound size, such as VeVMD, include inter-rater reliability and intra-rater reliability. Inter-rater reliability is important because clinical and research environments often dictate that different persons (or raters) perform wound measures over time. It is not realistic that a single rater will always be available. Therefore, it is critical to establish that an acceptable level of agreement exists among raters. Despite the fact that multiple raters are often involved in measures of wound size, it is also important to establish intra-rater reliability, or the consistency of repeated measures by the same rater.
Several factors may contribute to unreliable determinations of wound volume using computerized analyses of digital images, and VeVMD specifically. One contributor to variable measures is the dependence of VeVMD on the rater to define the outline of the wound margin and depth.